arg.version is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.
This issue was detected with the help of Smatch:
drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:4526 vmw_execbuf_ioctl() warn: potential spectre issue 'copy_offset' [w]
Fix this by sanitizing arg.version before using it to index copy_offset
Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].
[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
Cc: stable@vger.kernel.org Signed-off-by: Gustavo A. R. Silva gustavo@embeddedor.com --- drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c index 1f13457..ad91c6e 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c @@ -25,6 +25,7 @@ * **************************************************************************/ #include <linux/sync_file.h> +#include <linux/nospec.h>
#include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, return -EINVAL; }
- if (arg.version > 1 && - copy_from_user(&arg.context_handle, + if (arg.version >= ARRAY_SIZE(copy_offset)) + return -EFAULT; + arg.version = array_index_nospec(arg.version, ARRAY_SIZE(copy_offset)); + if (copy_from_user(&arg.context_handle, (void __user *) (data + copy_offset[0]), copy_offset[arg.version - 1] - copy_offset[0]) != 0)
Looks good to me based on my limited understanding. Thomas/Sinclair can could you please review and then we can include this in drm-fixes.
Thanks, Deepak
arg.version is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.
This issue was detected with the help of Smatch:
drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:4526 vmw_execbuf_ioctl() warn: potential spectre issue 'copy_offset' [w]
Fix this by sanitizing arg.version before using it to index copy_offset
Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].
[1] https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmarc.i nfo%2F%3Fl%3Dlinux- kernel%26m%3D152449131114778%26w%3D2&data=02%7C01%7Clinux- graphics- maintainer%40vmware.com%7Cf010b707b8ef4896c1a908d603aebcc6%7Cb39 138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636700446365603728& sdata=0D8lnUScxOmCCWXLHh8Otc3o%2F1yF1SxgGwIklRdMlXY%3D&re served=0
Cc: stable@vger.kernel.org Signed-off-by: Gustavo A. R. Silva gustavo@embeddedor.com
drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c index 1f13457..ad91c6e 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c @@ -25,6 +25,7 @@
****************/ #include <linux/sync_file.h> +#include <linux/nospec.h>
#include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, return -EINVAL; }
- if (arg.version > 1 &&
copy_from_user(&arg.context_handle,
- if (arg.version >= ARRAY_SIZE(copy_offset))
return -EFAULT;- arg.version = array_index_nospec(arg.version,
ARRAY_SIZE(copy_offset));
- if (copy_from_user(&arg.context_handle, (void __user *) (data + copy_offset[0]), copy_offset[arg.version - 1] - copy_offset[0]) != 0)
-- 2.7.4
Sent to linux-graphics-maintainer@vmware.com
On 08/20/2018 10:53 PM, Deepak Singh Rawat wrote:
Looks good to me based on my limited understanding. Thomas/Sinclair can could you please review and then we can include this in drm-fixes.
Thanks, Deepak
arg.version is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.
This issue was detected with the help of Smatch:
drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:4526 vmw_execbuf_ioctl() warn: potential spectre issue 'copy_offset' [w]
Fix this by sanitizing arg.version before using it to index copy_offset
Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].
[1]
Cc: stable@vger.kernel.org Signed-off-by: Gustavo A. R. Silva gustavo@embeddedor.com
drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c index 1f13457..ad91c6e 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c @@ -25,6 +25,7 @@
****************/ #include <linux/sync_file.h> +#include <linux/nospec.h>
#include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, return -EINVAL; }
- if (arg.version > 1 &&
copy_from_user(&arg.context_handle,
- if (arg.version >= ARRAY_SIZE(copy_offset))
return -EFAULT;
I must admit my understanding of spectre workings in this case is limited, but why do you need to compare arg.version against ARRAY_SIZE here, when it is already checked against DRM_VMW_EXECBUF_VERSION earlier?
- arg.version = array_index_nospec(arg.version,
ARRAY_SIZE(copy_offset));
- if (copy_from_user(&arg.context_handle, (void __user *) (data + copy_offset[0]), copy_offset[arg.version - 1] - copy_offset[0]) != 0)
Similarly, we want to perform this copy iff arg.version > 1. Why did you remove that check?
Thanks, Thomas
-- 2.7.4
Sent to linux-graphics-maintainer@vmware.com
Hi all,
On 8/21/18 3:19 AM, Thomas Hellstrom wrote:
#include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, return -EINVAL; }
- if (arg.version > 1 && - copy_from_user(&arg.context_handle, + if (arg.version >= ARRAY_SIZE(copy_offset)) + return -EFAULT;
I must admit my understanding of spectre workings in this case is limited, but why do you need to compare arg.version against ARRAY_SIZE here, when it is already checked against DRM_VMW_EXECBUF_VERSION earlier?
Oh, I wasn't aware of the value in DRM_VMW_EXECBUF_VERSION. But as arg.version is used to index copy_offset, it is safer to compare its value against the actual size of copy_offset.
So, what do you think if I replace DRM_VMW_EXECBUF_VERSION with ARRAY_SIZE instead of adding a new check against ARRAY_SIZE?
Something like:
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c index 1f13457..3ef9f7b 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c @@ -25,6 +25,7 @@ * **************************************************************************/ #include <linux/sync_file.h> +#include <linux/nospec.h>
#include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4514,11 +4515,12 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, * arg.version. */
- if (unlikely(arg.version > DRM_VMW_EXECBUF_VERSION || + if (unlikely(arg.version > ARRAY_SIZE(copy_offset) || arg.version == 0)) { DRM_ERROR("Incorrect execbuf version.\n"); return -EINVAL; } + arg.version = array_index_nospec(arg.version, ARRAY_SIZE(copy_offset));
if (arg.version > 1 && copy_from_user(&arg.context_handle,
+ arg.version = array_index_nospec(arg.version, ARRAY_SIZE(copy_offset)); + if (copy_from_user(&arg.context_handle, (void __user *) (data + copy_offset[0]), copy_offset[arg.version - 1] - copy_offset[0]) != 0)
Similarly, we want to perform this copy iff arg.version > 1. Why did you remove that check?
Yeah, this check must remain in place. I will add it back and send v2.
Thanks for the feedback! -- Gustavo
dri-devel@lists.freedesktop.org
-
Deepak Singh Rawat -
Gustavo A. R. Silva -
Thomas Hellstrom