On 23/02/2021 15:51, Neil Roberts wrote:
When a buffer is madvised as not needed and then purged, any attempts to
access the buffer from user-space should cause a bus fault. This patch
adds a check for that.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 17acb9f35ed7 ("drm/shmem: Add madvise state and purge helpers")
Signed-off-by: Neil Roberts <nroberts@xxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 9825c378dfa6..b26139b1dc35 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -525,14 +525,24 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
struct drm_gem_object *obj = vma->vm_private_data;
struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
loff_t num_pages = obj->size >> PAGE_SHIFT;
+ vm_fault_t ret;
struct page *page;
- if (vmf->pgoff >= num_pages || WARN_ON_ONCE(!shmem->pages))
- return VM_FAULT_SIGBUS;
+ mutex_lock(&shmem->pages_lock);
+
+ if (vmf->pgoff >= num_pages ||
+ WARN_ON_ONCE(!shmem->pages) ||
+ shmem->madv < 0) {
+ ret = VM_FAULT_SIGBUS;
+ } else {
+ page = shmem->pages[vmf->pgoff];
- page = shmem->pages[vmf->pgoff];
+ ret = vmf_insert_page(vma, vmf->address, page);
+ }
- return vmf_insert_page(vma, vmf->address, page);
+ mutex_unlock(&shmem->pages_lock);
+
+ return ret;
}
static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
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