vc4_gem_object_mmap() rejects a writable mapping of a validated shader
BO, but leaves VM_MAYWRITE set. Userspace can map the BO read-only and
then turn it writable with mprotect().
Validated shader BOs must stay read-only: the validator checks the
instructions once and the GPU trusts them afterwards. A writable
mapping lets userspace rewrite the code after validation, bypassing the
validator.
Clear VM_MAYWRITE on the read-only path so the mapping cannot be
upgraded, as i915 already does for its read-only objects.
Fixes: 463873d57014 ("drm/vc4: Add an API for creating GPU shaders in GEM BOs.")
Cc: [email protected]
Reported-by: [email protected]
Closes:
https://lore.kernel.org/dri-devel/[email protected]/
Signed-off-by: Linmao Li <[email protected]>
---
drivers/gpu/drm/vc4/vc4_bo.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
index 2161761b1f22..5e7c46dd7823 100644
--- a/drivers/gpu/drm/vc4/vc4_bo.c
+++ b/drivers/gpu/drm/vc4/vc4_bo.c
@@ -732,9 +732,13 @@ static int vc4_gem_object_mmap(struct drm_gem_object *obj,
struct vm_area_struct
{
struct vc4_bo *bo = to_vc4_bo(obj);
- if (bo->validated_shader && (vma->vm_flags & VM_WRITE)) {
- DRM_DEBUG("mmapping of shader BOs for writing not allowed.\n");
- return -EINVAL;
+ if (bo->validated_shader) {
+ if (vma->vm_flags & VM_WRITE) {
+ DRM_DEBUG("mmapping of shader BOs for writing not
allowed.\n");
+ return -EINVAL;
+ }
+
+ vm_flags_clear(vma, VM_MAYWRITE);
}
mutex_lock(&bo->madv_lock);
--
2.25.1
