When handling a GPU page fault addr_to_drm_mm_node() is used to translate the GPU address to a buffer object. However it is possible for the buffer object to be freed after the function has returned resulting in a use-after-free of the BO.
Change addr_to_drm_mm_node to return the panfrost_gem_object with an extra reference on it, preventing the BO from being freed until after the page fault has been handled.
Signed-off-by: Steven Price steven.price@arm.com ---
I've managed to trigger this, generating the following stack trace.
Unable to handle kernel NULL pointer dereference at virtual address 00000090 pgd = 33a6a181 [00000090] *pgd=00000000 Internal error: Oops: 5 [#1] SMP ARM Modules linked in: CPU: 0 PID: 81 Comm: irq/60-mmu Not tainted 5.3.0-rc1+ #4 Hardware name: Rockchip (Device Tree) PC is at panfrost_mmu_map_fault_addr+0x140/0x3a0 LR is at _raw_spin_unlock+0x20/0x3c pc : [<c0508944>] lr : [<c07ced10>] psr: 20030013 sp : ec643e88 ip : ea70ce24 fp : ec5fe840 r10: 00000001 r9 : 00000000 r8 : 000178c9 r7 : 00000000 r6 : 178c9f00 r5 : ec5fe940 r4 : ea70ce08 r3 : 00000000 r2 : 00000000 r1 : ec640e00 r0 : ec5fe940 Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: 29f8406a DAC: 00000051 Process irq/60-mmu (pid: 81, stack limit = 0x4b907106) Stack: (0xec643e88 to 0xec644000) 3e80: ec640e00 c07cede0 c0c0b200 ec640e00 00000000 00000000 3ea0: 000178c9 00000000 c0c0b200 c07cede0 eef91040 ec5fe840 00000001 00000000 3ec0: 00010001 010003c3 000000c3 00000001 178c9f00 c0508c98 eef91050 00000000 3ee0: ec643f34 c07c9188 00000001 c0167854 00000000 ec643ef8 c0c08448 c07c933c 3f00: 00000000 ec643f04 fffefffe 3d182b17 ee193468 ee193400 ec5db3c0 ec5db3c0 3f20: c0183840 ec5db3e4 c0cb2874 c0183b08 00000001 c018385c ffffe000 ee193400 3f40: ec5db3c0 c0183b8c c0c08448 00000000 60000013 00000000 c01839b8 3d182b17 3f60: ffffe000 ec5d0500 ec5db380 ec642000 ec5db3c0 c0183a64 00000000 ed025cd8 3f80: ec5d0538 c0146cfc ec642000 ec5db380 c0146bc0 00000000 00000000 00000000 3fa0: 00000000 00000000 00000000 c01010b4 00000000 00000000 00000000 00000000 3fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 3fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000 [<c0508944>] (panfrost_mmu_map_fault_addr) from [<c0508c98>] (panfrost_mmu_irq_handler_thread+0xf4/0x248) [<c0508c98>] (panfrost_mmu_irq_handler_thread) from [<c018385c>] (irq_thread_fn+0x1c/0x58) [<c018385c>] (irq_thread_fn) from [<c0183b8c>] (irq_thread+0x128/0x240) [<c0183b8c>] (irq_thread) from [<c0146cfc>] (kthread+0x13c/0x154) [<c0146cfc>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20) Exception stack(0xec643fb0 to 0xec643ff8) 3fa0: 00000000 00000000 00000000 00000000 3fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 3fe0: 00000000 00000000 00000000 00000000 00000013 00000000 Code: 1affffec eaffffe8 e5143004 e59d2014 (e5933090) ---[ end trace 04eadc3009b8f507 ]--- --- drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 ++++++++++++++++--------- 1 file changed, 24 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c index 842bdd7cf6be..115925e7460a 100644 --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c @@ -392,9 +392,11 @@ void panfrost_mmu_pgtable_free(struct panfrost_file_priv *priv) free_io_pgtable_ops(mmu->pgtbl_ops); }
-static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr) +static struct panfrost_gem_object * +addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr) { - struct drm_mm_node *node = NULL; + struct panfrost_gem_object *bo = NULL; + struct drm_mm_node *node; u64 offset = addr >> PAGE_SHIFT; struct panfrost_mmu *mmu;
@@ -406,14 +408,17 @@ static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device *pfdev, in
priv = container_of(mmu, struct panfrost_file_priv, mmu); drm_mm_for_each_node(node, &priv->mm) { - if (offset >= node->start && offset < (node->start + node->size)) + if (offset >= node->start && + offset < (node->start + node->size)) { + bo = drm_mm_node_to_panfrost_bo(node); + drm_gem_object_get(&bo->base.base); goto out; + } } } - out: spin_unlock(&pfdev->as_lock); - return node; + return bo; }
#define NUM_FAULT_PAGES (SZ_2M / PAGE_SIZE) @@ -421,29 +426,28 @@ static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device *pfdev, in int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, u64 addr) { int ret, i; - struct drm_mm_node *node; struct panfrost_gem_object *bo; struct address_space *mapping; pgoff_t page_offset; struct sg_table *sgt; struct page **pages;
- node = addr_to_drm_mm_node(pfdev, as, addr); - if (!node) + bo = addr_to_drm_mm_node(pfdev, as, addr); + if (!bo) return -ENOENT;
- bo = drm_mm_node_to_panfrost_bo(node); if (!bo->is_heap) { dev_WARN(pfdev->dev, "matching BO is not heap type (GPU VA = %llx)", - node->start << PAGE_SHIFT); - return -EINVAL; + bo->node.start << PAGE_SHIFT); + ret = -EINVAL; + goto err_bo; } WARN_ON(bo->mmu->as != as);
/* Assume 2MB alignment and size multiple */ addr &= ~((u64)SZ_2M - 1); page_offset = addr >> PAGE_SHIFT; - page_offset -= node->start; + page_offset -= bo->node.start;
mutex_lock(&bo->base.pages_lock);
@@ -452,7 +456,8 @@ int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, u64 addr) sizeof(struct sg_table), GFP_KERNEL | __GFP_ZERO); if (!bo->sgts) { mutex_unlock(&bo->base.pages_lock); - return -ENOMEM; + ret = -ENOMEM; + goto err_bo; }
pages = kvmalloc_array(bo->base.base.size >> PAGE_SHIFT, @@ -461,7 +466,8 @@ int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, u64 addr) kfree(bo->sgts); bo->sgts = NULL; mutex_unlock(&bo->base.pages_lock); - return -ENOMEM; + ret = -ENOMEM; + goto err_bo; } bo->base.pages = pages; bo->base.pages_use_count = 1; @@ -499,12 +505,16 @@ int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, u64 addr)
dev_dbg(pfdev->dev, "mapped page fault @ AS%d %llx", as, addr);
+ drm_gem_object_put_unlocked(&bo->base.base); + return 0;
err_map: sg_free_table(sgt); err_pages: drm_gem_shmem_put_pages(&bo->base); +err_bo: + drm_gem_object_put_unlocked(&bo->base.base); return ret; }