We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org --- drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 49 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG + bool "DMA-BUF debug checks" + default y if DMA_API_DEBUG + help + This option enables additional checks for DMA-BUF importers and + exporters. Specifically it validates that importers do not peek at the + underlying struct page when they import a buffer. + config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..6e4725f7dfde 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,30 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, + enum dma_data_direction direction) +{ + struct sg_table *sg_table; + + sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + +#if CONFIG_DMABUF_DEBUG + if (sg_table) { + int i; + struct scatterlist *sg; + + /* To catch abuse of the underlying struct page by importers mix + * up the bits, but take care to preserve the low SG_ bits to + * not corrupt the sgt. The mixing is undone in __unmap_dma_buf + * before passing the sgt back to the exporter. */ + for_each_sgtable_sg(sg_table, sg, i) + sg->page_link ^= ~0xffUL; + } +#endif + + return sg_table; +} + /** * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to. @@ -737,7 +761,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
- sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL); + sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL); if (!sgt) sgt = ERR_PTR(-ENOMEM); if (IS_ERR(sgt)) { @@ -784,6 +808,23 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction) +{ + +#if CONFIG_DMABUF_DEBUG + if (sg_table) { + int i; + struct scatterlist *sg; + + for_each_sgtable_sg(sg_table, sg, i) + sg->page_link ^= ~0xffUL; + } +#endif + attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); +} + /** * dma_buf_detach - Remove the given attachment from dmabuf's attachments list * @dmabuf: [in] buffer to detach from. @@ -802,7 +843,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
- dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir); + __unmap_dma_buf(attach, attach->sgt, attach->dir);
if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach); @@ -924,7 +965,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1028,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); + __unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked. + * + * Note that exporters should not try to cache the scatter list, or + * return the same one for multiple calls. Caching is done either by the + * DMA-BUF code (for non-dynamic importers) or the importer. Ownership + * of the scatter list is transferred to the caller, and returned by + * @unmap_dma_buf. */ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, enum dma_data_direction);
Am 15.01.21 um 14:02 schrieb Daniel Vetter:
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org
drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 49 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG
- bool "DMA-BUF debug checks"
- default y if DMA_API_DEBUG
- help
This option enables additional checks for DMA-BUF importers andexporters. Specifically it validates that importers do not peek at theunderlying struct page when they import a buffer.- config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..6e4725f7dfde 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,30 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
enum dma_data_direction direction)+{
- struct sg_table *sg_table;
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+#if CONFIG_DMABUF_DEBUG
- if (sg_table) {
int i;struct scatterlist *sg;/* To catch abuse of the underlying struct page by importers mix* up the bits, but take care to preserve the low SG_ bits to* not corrupt the sgt. The mixing is undone in __unmap_dma_buf* before passing the sgt back to the exporter. */for_each_sgtable_sg(sg_table, sg, i)sg->page_link ^= ~0xffUL;- }
+#endif
- return sg_table;
+}
- /**
- dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
- @dmabuf: [in] buffer to attach device to.
@@ -737,7 +761,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL);@@ -784,6 +808,23 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
struct sg_table *sg_table,enum dma_data_direction direction)+{
+#if CONFIG_DMABUF_DEBUG
- if (sg_table) {
int i;struct scatterlist *sg;for_each_sgtable_sg(sg_table, sg, i)sg->page_link ^= ~0xffUL;- }
+#endif
Instead of duplicating this I would rather structure the code so that we have a helper to mangle the sgt when necessary.
This can then be called from both the map() as well as the unmap() path.
Apart from that looks good to me, Christian.
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+}
- /**
- dma_buf_detach - Remove the given attachment from dmabuf's attachments list
- @dmabuf: [in] buffer to detach from.
@@ -802,7 +843,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
__unmap_dma_buf(attach, attach->sgt, attach->dir);if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach);
@@ -924,7 +965,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1028,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
__unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked.
** Note that exporters should not try to cache the scatter list, or* return the same one for multiple calls. Caching is done either by the* DMA-BUF code (for non-dynamic importers) or the importer. Ownership* of the scatter list is transferred to the caller, and returned by* @unmap_dma_buf.
On Fri, Jan 15, 2021 at 2:09 PM Christian König ckoenig.leichtzumerken@gmail.com wrote:
Am 15.01.21 um 14:02 schrieb Daniel Vetter:
have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org
drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 49 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG
bool "DMA-BUF debug checks"default y if DMA_API_DEBUGhelpThis option enables additional checks for DMA-BUF importers andexporters. Specifically it validates that importers do not peek at theunderlying struct page when they import a buffer.- config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..6e4725f7dfde 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,30 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
enum dma_data_direction direction)+{
struct sg_table *sg_table;sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);+#if CONFIG_DMABUF_DEBUG
if (sg_table) {int i;struct scatterlist *sg;/* To catch abuse of the underlying struct page by importers mix* up the bits, but take care to preserve the low SG_ bits to* not corrupt the sgt. The mixing is undone in __unmap_dma_buf* before passing the sgt back to the exporter. */for_each_sgtable_sg(sg_table, sg, i)sg->page_link ^= ~0xffUL;}+#endif
return sg_table;+}
- /**
- dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
- @dmabuf: [in] buffer to attach device to.
@@ -737,7 +761,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL); if (!sgt) sgt = ERR_PTR(-ENOMEM); if (IS_ERR(sgt)) {@@ -784,6 +808,23 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
struct sg_table *sg_table,enum dma_data_direction direction)+{
+#if CONFIG_DMABUF_DEBUG
if (sg_table) {int i;struct scatterlist *sg;for_each_sgtable_sg(sg_table, sg, i)sg->page_link ^= ~0xffUL;}+#endif
Instead of duplicating this I would rather structure the code so that we have a helper to mangle the sgt when necessary.
This can then be called from both the map() as well as the unmap() path.
Well that's why extracted the helper functions (it would be 4 copies otherwise). It's true that it's still 2x the same operation, but conceptually one of them mangles, the other unmangles the pointers. It's just that with XOR mangling, that's both the same code. Readability feels better that way to me, but I guess I can do another tiny helper function extraction if you insist? -Daniel
Apart from that looks good to me, Christian.
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);+}
- /**
- dma_buf_detach - Remove the given attachment from dmabuf's attachments list
- @dmabuf: [in] buffer to detach from.
@@ -802,7 +843,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
__unmap_dma_buf(attach, attach->sgt, attach->dir); if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach);@@ -924,7 +965,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);@@ -987,7 +1028,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
__unmap_dma_buf(attach, sg_table, direction); if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked.
** Note that exporters should not try to cache the scatter list, or* return the same one for multiple calls. Caching is done either by the* DMA-BUF code (for non-dynamic importers) or the importer. Ownership* of the scatter list is transferred to the caller, and returned by* @unmap_dma_buf. */ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, enum dma_data_direction);
Am 15.01.21 um 14:22 schrieb Daniel Vetter:
On Fri, Jan 15, 2021 at 2:09 PM Christian König ckoenig.leichtzumerken@gmail.com wrote:
Am 15.01.21 um 14:02 schrieb Daniel Vetter:
have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org
drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 49 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG
bool "DMA-BUF debug checks"default y if DMA_API_DEBUGhelpThis option enables additional checks for DMA-BUF importers andexporters. Specifically it validates that importers do not peek at theunderlying struct page when they import a buffer.- config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..6e4725f7dfde 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,30 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
enum dma_data_direction direction)+{
struct sg_table *sg_table;sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);+#if CONFIG_DMABUF_DEBUG
if (sg_table) {int i;struct scatterlist *sg;/* To catch abuse of the underlying struct page by importers mix* up the bits, but take care to preserve the low SG_ bits to* not corrupt the sgt. The mixing is undone in __unmap_dma_buf* before passing the sgt back to the exporter. */for_each_sgtable_sg(sg_table, sg, i)sg->page_link ^= ~0xffUL;}+#endif
return sg_table;+}
- /**
- dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
- @dmabuf: [in] buffer to attach device to.
@@ -737,7 +761,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL); if (!sgt) sgt = ERR_PTR(-ENOMEM); if (IS_ERR(sgt)) {@@ -784,6 +808,23 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
struct sg_table *sg_table,enum dma_data_direction direction)+{
+#if CONFIG_DMABUF_DEBUG
if (sg_table) {int i;struct scatterlist *sg;for_each_sgtable_sg(sg_table, sg, i)sg->page_link ^= ~0xffUL;}+#endif
Instead of duplicating this I would rather structure the code so that we have a helper to mangle the sgt when necessary.
This can then be called from both the map() as well as the unmap() path.
Well that's why extracted the helper functions (it would be 4 copies otherwise). It's true that it's still 2x the same operation, but conceptually one of them mangles, the other unmangles the pointers. It's just that with XOR mangling, that's both the same code. Readability feels better that way to me, but I guess I can do another tiny helper function extraction if you insist?
I think it would be better to have only one.
And I insist that the mangle value is only once somewhere, either use just one function or a define/constant.
Christian.
-Daniel
Apart from that looks good to me, Christian.
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);+}
- /**
- dma_buf_detach - Remove the given attachment from dmabuf's attachments list
- @dmabuf: [in] buffer to detach from.
@@ -802,7 +843,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
__unmap_dma_buf(attach, attach->sgt, attach->dir); if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach);@@ -924,7 +965,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);@@ -987,7 +1028,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
__unmap_dma_buf(attach, sg_table, direction); if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked.
** Note that exporters should not try to cache the scatter list, or* return the same one for multiple calls. Caching is done either by the* DMA-BUF code (for non-dynamic importers) or the importer. Ownership* of the scatter list is transferred to the caller, and returned by* @unmap_dma_buf. */ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, enum dma_data_direction);
Hi Daniel,
I love your patch! Perhaps something to improve:
[auto build test WARNING on next-20210115] [also build test WARNING on v5.11-rc3] [cannot apply to tegra-drm/drm/tegra/for-next linus/master v5.11-rc3 v5.11-rc2 v5.11-rc1] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch]
url: https://github.com/0day-ci/linux/commits/Daniel-Vetter/drm-buf-Add-debug-opt... base: b3a3cbdec55b090d22a09f75efb7c7d34cb97f25 config: i386-randconfig-a012-20210115 (attached as .config) compiler: gcc-9 (Debian 9.3.0-15) 9.3.0 reproduce (this is a W=1 build): # https://github.com/0day-ci/linux/commit/a0f2603f574f0a1aedd7719cbb47b807796d... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Daniel-Vetter/drm-buf-Add-debug-option/20210115-210650 git checkout a0f2603f574f0a1aedd7719cbb47b807796d2367 # save the attached .config to linux build tree make W=1 ARCH=i386
If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot lkp@intel.com
All warnings (new ones prefixed by >>):
drivers/dma-buf/dma-buf.c: In function '__map_dma_buf':
drivers/dma-buf/dma-buf.c:676:5: warning: "CONFIG_DMABUF_DEBUG" is not defined, evaluates to 0 [-Wundef]
676 | #if CONFIG_DMABUF_DEBUG | ^~~~~~~~~~~~~~~~~~~ drivers/dma-buf/dma-buf.c: In function '__unmap_dma_buf': drivers/dma-buf/dma-buf.c:816:5: warning: "CONFIG_DMABUF_DEBUG" is not defined, evaluates to 0 [-Wundef] 816 | #if CONFIG_DMABUF_DEBUG | ^~~~~~~~~~~~~~~~~~~
vim +/CONFIG_DMABUF_DEBUG +676 drivers/dma-buf/dma-buf.c
668 669 static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, 670 enum dma_data_direction direction) 671 { 672 struct sg_table *sg_table; 673 674 sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); 675
676 #if CONFIG_DMABUF_DEBUG
677 if (sg_table) { 678 int i; 679 struct scatterlist *sg; 680 681 /* To catch abuse of the underlying struct page by importers mix 682 * up the bits, but take care to preserve the low SG_ bits to 683 * not corrupt the sgt. The mixing is undone in __unmap_dma_buf 684 * before passing the sgt back to the exporter. */ 685 for_each_sgtable_sg(sg_table, sg, i) 686 sg->page_link ^= ~0xffUL; 687 } 688 #endif 689 690 return sg_table; 691 } 692
--- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
v3: Only one copy of the mangle/unmangle code (Christian)
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk (v2) Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org --- drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 48 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 58 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG + bool "DMA-BUF debug checks" + default y if DMA_API_DEBUG + help + This option enables additional checks for DMA-BUF importers and + exporters. Specifically it validates that importers do not peek at the + underlying struct page when they import a buffer. + config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..820927474cc8 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,36 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static void mangle_sg_table(struct sg_table *sg_table) +{ +#if CONFIG_DMABUF_DEBUG + int i; + struct scatterlist *sg; + + if (!sg_table) + return; + + /* To catch abuse of the underlying struct page by importers mix + * up the bits, but take care to preserve the low SG_ bits to + * not corrupt the sgt. The mixing is undone in __unmap_dma_buf + * before passing the sgt back to the exporter. */ + for_each_sgtable_sg(sg_table, sg, i) + sg->page_link ^= ~0xffUL; +#endif + +} +static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, + enum dma_data_direction direction) +{ + struct sg_table *sg_table; + + sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + + mangle_sg_table(sg_table); + + return sg_table; +} + /** * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to. @@ -737,7 +767,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
- sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL); + sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL); if (!sgt) sgt = ERR_PTR(-ENOMEM); if (IS_ERR(sgt)) { @@ -784,6 +814,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction) +{ + /* uses XOR, hence this unmangles */ + mangle_sg_table(sg_table); + + attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); +} + /** * dma_buf_detach - Remove the given attachment from dmabuf's attachments list * @dmabuf: [in] buffer to detach from. @@ -802,7 +842,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
- dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir); + __unmap_dma_buf(attach, attach->sgt, attach->dir);
if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach); @@ -924,7 +964,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1027,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); + __unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked. + * + * Note that exporters should not try to cache the scatter list, or + * return the same one for multiple calls. Caching is done either by the + * DMA-BUF code (for non-dynamic importers) or the importer. Ownership + * of the scatter list is transferred to the caller, and returned by + * @unmap_dma_buf. */ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, enum dma_data_direction);
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
v3: Only one copy of the mangle/unmangle code (Christian)
v4: #ifdef, not #if (0day)
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk (v2) Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org --- drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 48 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 58 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG + bool "DMA-BUF debug checks" + default y if DMA_API_DEBUG + help + This option enables additional checks for DMA-BUF importers and + exporters. Specifically it validates that importers do not peek at the + underlying struct page when they import a buffer. + config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..f676bab64f55 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,36 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static void mangle_sg_table(struct sg_table *sg_table) +{ +#ifdef CONFIG_DMABUF_DEBUG + int i; + struct scatterlist *sg; + + if (!sg_table) + return; + + /* To catch abuse of the underlying struct page by importers mix + * up the bits, but take care to preserve the low SG_ bits to + * not corrupt the sgt. The mixing is undone in __unmap_dma_buf + * before passing the sgt back to the exporter. */ + for_each_sgtable_sg(sg_table, sg, i) + sg->page_link ^= ~0xffUL; +#endif + +} +static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, + enum dma_data_direction direction) +{ + struct sg_table *sg_table; + + sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + + mangle_sg_table(sg_table); + + return sg_table; +} + /** * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to. @@ -737,7 +767,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
- sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL); + sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL); if (!sgt) sgt = ERR_PTR(-ENOMEM); if (IS_ERR(sgt)) { @@ -784,6 +814,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction) +{ + /* uses XOR, hence this unmangles */ + mangle_sg_table(sg_table); + + attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); +} + /** * dma_buf_detach - Remove the given attachment from dmabuf's attachments list * @dmabuf: [in] buffer to detach from. @@ -802,7 +842,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
- dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir); + __unmap_dma_buf(attach, attach->sgt, attach->dir);
if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach); @@ -924,7 +964,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1027,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); + __unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked. + * + * Note that exporters should not try to cache the scatter list, or + * return the same one for multiple calls. Caching is done either by the + * DMA-BUF code (for non-dynamic importers) or the importer. Ownership + * of the scatter list is transferred to the caller, and returned by + * @unmap_dma_buf. */ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, enum dma_data_direction);
Quoting Daniel Vetter (2021-01-15 15:52:26)
+static void mangle_sg_table(struct sg_table *sg_table) +{ +#ifdef CONFIG_DMABUF_DEBUG
int i;struct scatterlist *sg;if (!sg_table)
if (!IS_ENABLED(CONFIG_DMABUF_DEBUG) || IS_ERR_OR_NULL(sg_table))
return;
Although NULL is not meant to be returned. -Chris
Am 15.01.21 um 16:52 schrieb Daniel Vetter:
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
v3: Only one copy of the mangle/unmangle code (Christian)
v4: #ifdef, not #if (0day)
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk (v2) Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org
drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 48 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 58 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG
- bool "DMA-BUF debug checks"
- default y if DMA_API_DEBUG
- help
This option enables additional checks for DMA-BUF importers andexporters. Specifically it validates that importers do not peek at theunderlying struct page when they import a buffer.- config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..f676bab64f55 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,36 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static void mangle_sg_table(struct sg_table *sg_table) +{ +#ifdef CONFIG_DMABUF_DEBUG
- int i;
- struct scatterlist *sg;
- if (!sg_table)
At least in the map case the sg_table returned could also be an ERR_PTR().
Might be even better to drop the __map_dma_buf wrappers and call the mangle after the error handling.
Christian.
return;- /* To catch abuse of the underlying struct page by importers mix
* up the bits, but take care to preserve the low SG_ bits to* not corrupt the sgt. The mixing is undone in __unmap_dma_buf* before passing the sgt back to the exporter. */- for_each_sgtable_sg(sg_table, sg, i)
sg->page_link ^= ~0xffUL;+#endif
+} +static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
enum dma_data_direction direction)+{
- struct sg_table *sg_table;
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- mangle_sg_table(sg_table);
- return sg_table;
+}
- /**
- dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
- @dmabuf: [in] buffer to attach device to.
@@ -737,7 +767,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL);@@ -784,6 +814,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
struct sg_table *sg_table,enum dma_data_direction direction)+{
- /* uses XOR, hence this unmangles */
- mangle_sg_table(sg_table);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+}
- /**
- dma_buf_detach - Remove the given attachment from dmabuf's attachments list
- @dmabuf: [in] buffer to detach from.
@@ -802,7 +842,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
__unmap_dma_buf(attach, attach->sgt, attach->dir);if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach);
@@ -924,7 +964,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1027,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
__unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked.
** Note that exporters should not try to cache the scatter list, or* return the same one for multiple calls. Caching is done either by the* DMA-BUF code (for non-dynamic importers) or the importer. Ownership* of the scatter list is transferred to the caller, and returned by* @unmap_dma_buf.
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
v3: Only one copy of the mangle/unmangle code (Christian)
v4: #ifdef, not #if (0day)
v5: sg_table can also be an ERR_PTR (Chris, Christian)
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk (v2) Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org --- drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 46 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 56 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG + bool "DMA-BUF debug checks" + default y if DMA_API_DEBUG + help + This option enables additional checks for DMA-BUF importers and + exporters. Specifically it validates that importers do not peek at the + underlying struct page when they import a buffer. + config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..f264b70c383e 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,34 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static void mangle_sg_table(struct sg_table *sg_table) +{ +#ifdef CONFIG_DMABUF_DEBUG + int i; + struct scatterlist *sg; + + /* To catch abuse of the underlying struct page by importers mix + * up the bits, but take care to preserve the low SG_ bits to + * not corrupt the sgt. The mixing is undone in __unmap_dma_buf + * before passing the sgt back to the exporter. */ + for_each_sgtable_sg(sg_table, sg, i) + sg->page_link ^= ~0xffUL; +#endif + +} +static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, + enum dma_data_direction direction) +{ + struct sg_table *sg_table; + + sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + + if (!IS_ERR_OR_NULL(sg_table)) + mangle_sg_table(sg_table); + + return sg_table; +} + /** * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to. @@ -737,7 +765,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
- sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL); + sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL); if (!sgt) sgt = ERR_PTR(-ENOMEM); if (IS_ERR(sgt)) { @@ -784,6 +812,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction) +{ + /* uses XOR, hence this unmangles */ + mangle_sg_table(sg_table); + + attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); +} + /** * dma_buf_detach - Remove the given attachment from dmabuf's attachments list * @dmabuf: [in] buffer to detach from. @@ -802,7 +840,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
- dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir); + __unmap_dma_buf(attach, attach->sgt, attach->dir);
if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach); @@ -924,7 +962,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); + sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1025,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction); + __unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked. + * + * Note that exporters should not try to cache the scatter list, or + * return the same one for multiple calls. Caching is done either by the + * DMA-BUF code (for non-dynamic importers) or the importer. Ownership + * of the scatter list is transferred to the caller, and returned by + * @unmap_dma_buf. */ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, enum dma_data_direction);
Am 15.01.21 um 17:47 schrieb Daniel Vetter:
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
v3: Only one copy of the mangle/unmangle code (Christian)
v4: #ifdef, not #if (0day)
v5: sg_table can also be an ERR_PTR (Chris, Christian)
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk (v2) Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 46 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 56 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers.
+config DMABUF_DEBUG
- bool "DMA-BUF debug checks"
- default y if DMA_API_DEBUG
- help
This option enables additional checks for DMA-BUF importers andexporters. Specifically it validates that importers do not peek at theunderlying struct page when they import a buffer.- config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..f264b70c383e 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,34 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put);
+static void mangle_sg_table(struct sg_table *sg_table) +{ +#ifdef CONFIG_DMABUF_DEBUG
- int i;
- struct scatterlist *sg;
- /* To catch abuse of the underlying struct page by importers mix
* up the bits, but take care to preserve the low SG_ bits to* not corrupt the sgt. The mixing is undone in __unmap_dma_buf* before passing the sgt back to the exporter. */- for_each_sgtable_sg(sg_table, sg, i)
sg->page_link ^= ~0xffUL;+#endif
+} +static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
enum dma_data_direction direction)+{
- struct sg_table *sg_table;
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- if (!IS_ERR_OR_NULL(sg_table))
mangle_sg_table(sg_table);- return sg_table;
+}
- /**
- dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
- @dmabuf: [in] buffer to attach device to.
@@ -737,7 +765,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL);@@ -784,6 +812,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
struct sg_table *sg_table,enum dma_data_direction direction)+{
- /* uses XOR, hence this unmangles */
- mangle_sg_table(sg_table);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+}
- /**
- dma_buf_detach - Remove the given attachment from dmabuf's attachments list
- @dmabuf: [in] buffer to detach from.
@@ -802,7 +840,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
__unmap_dma_buf(attach, attach->sgt, attach->dir);if (dma_buf_is_dynamic(attach->dmabuf)) { dma_buf_unpin(attach);
@@ -924,7 +962,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1025,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
__unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked.
** Note that exporters should not try to cache the scatter list, or* return the same one for multiple calls. Caching is done either by the* DMA-BUF code (for non-dynamic importers) or the importer. Ownership* of the scatter list is transferred to the caller, and returned by* @unmap_dma_buf.
On Fri, Jan 15, 2021 at 07:52:53PM +0100, Christian König wrote:
Am 15.01.21 um 17:47 schrieb Daniel Vetter:
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything.
I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules.
Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference.
v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris)
Enable by default when CONFIG_DMA_API_DEBUG is enabled.
v3: Only one copy of the mangle/unmangle code (Christian)
v4: #ifdef, not #if (0day)
v5: sg_table can also be an ERR_PTR (Chris, Christian)
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk (v2) Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: David Stevens stevensd@chromium.org Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Christian König christian.koenig@amd.com
Stuffed into drm-misc-next, thanks for reviewing to both of you. -Daniel
drivers/dma-buf/Kconfig | 8 +++++++ drivers/dma-buf/dma-buf.c | 46 +++++++++++++++++++++++++++++++++++---- include/linux/dma-buf.h | 6 +++++ 3 files changed, 56 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 4f8224a6ac95..4e16c71c24b7 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY This is marked experimental because we don't yet have a consistent execution context and memory management between drivers. +config DMABUF_DEBUG
- bool "DMA-BUF debug checks"
- default y if DMA_API_DEBUG
- help
This option enables additional checks for DMA-BUF importers andexporters. Specifically it validates that importers do not peek at theunderlying struct page when they import a buffer.- config DMABUF_SELFTESTS tristate "Selftests for the dma-buf interfaces" default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 1c9bd51db110..f264b70c383e 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -666,6 +666,34 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_GPL(dma_buf_put); +static void mangle_sg_table(struct sg_table *sg_table) +{ +#ifdef CONFIG_DMABUF_DEBUG
- int i;
- struct scatterlist *sg;
- /* To catch abuse of the underlying struct page by importers mix
* up the bits, but take care to preserve the low SG_ bits to* not corrupt the sgt. The mixing is undone in __unmap_dma_buf* before passing the sgt back to the exporter. */- for_each_sgtable_sg(sg_table, sg, i)
sg->page_link ^= ~0xffUL;+#endif
+} +static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
enum dma_data_direction direction)+{
- struct sg_table *sg_table;
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- if (!IS_ERR_OR_NULL(sg_table))
mangle_sg_table(sg_table);- return sg_table;
+}
- /**
- dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
- @dmabuf: [in] buffer to attach device to.
@@ -737,7 +765,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev, goto err_unlock; }
sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL);@@ -784,6 +812,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, } EXPORT_SYMBOL_GPL(dma_buf_attach); +static void __unmap_dma_buf(struct dma_buf_attachment *attach,
struct sg_table *sg_table,enum dma_data_direction direction)+{
- /* uses XOR, hence this unmangles */
- mangle_sg_table(sg_table);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+}
- /**
- dma_buf_detach - Remove the given attachment from dmabuf's attachments list
- @dmabuf: [in] buffer to detach from.
@@ -802,7 +840,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_lock(attach->dmabuf->resv, NULL);
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
__unmap_dma_buf(attach, attach->sgt, attach->dir);@@ -924,7 +962,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } }
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
- sg_table = __map_dma_buf(attach, direction); if (!sg_table) sg_table = ERR_PTR(-ENOMEM);
@@ -987,7 +1025,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, if (dma_buf_is_dynamic(attach->dmabuf)) dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
- __unmap_dma_buf(attach, sg_table, direction); if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..efdc56b9d95f 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -154,6 +154,12 @@ struct dma_buf_ops { * On failure, returns a negative error value wrapped into a pointer. * May also return -EINTR when a signal was received while being * blocked.
** Note that exporters should not try to cache the scatter list, or* return the same one for multiple calls. Caching is done either by the* DMA-BUF code (for non-dynamic importers) or the importer. Ownership* of the scatter list is transferred to the caller, and returned by* @unmap_dma_buf.
dri-devel@lists.freedesktop.org
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