drm/panthor: Fix UAF on kernel BO VA nodes

If the MMU is down, panthor_vm_unmap_range() might return an error.
We expect the page table to be updated still, and if the MMU is blocked,
the rest of the GPU should be blocked too, so no risk of accessing
physical memory returned to the system (which the current code doesn't
cover for anyway).

Proceed with the rest of the cleanup instead of bailing out and leaving
the va_node inserted in the drm_mm, which leads to UAF when other
adjacent nodes are removed from the drm_mm tree.

Reported-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Closes: https://gitlab.freedesktop.org/panfrost/linux/-/issues/57
Fixes: 8a1cc07578bf ("drm/panthor: Add GEM logical block")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20251031154818.821054-2-boris.brezillon@collabora.com
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 7e7d2f223cfa4d9556db5caf758b8926696ab462..f369cc3e2a5fa71251f0ee321d400d874a4f3380 100644 (file)
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -87,7 +87,6 @@ static void panthor_gem_free_object(struct drm_gem_object *obj)
 void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
 {
        struct panthor_vm *vm;
-       int ret;
 
        if (IS_ERR_OR_NULL(bo))
                return;
@@ -95,18 +94,11 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
        vm = bo->vm;
        panthor_kernel_bo_vunmap(bo);
 
-       if (drm_WARN_ON(bo->obj->dev,
-                       to_panthor_bo(bo->obj)->exclusive_vm_root_gem != panthor_vm_root_gem(vm)))
-               goto out_free_bo;
-
-       ret = panthor_vm_unmap_range(vm, bo->va_node.start, bo->va_node.size);
-       if (ret)
-               goto out_free_bo;
-
+       drm_WARN_ON(bo->obj->dev,
+                   to_panthor_bo(bo->obj)->exclusive_vm_root_gem != panthor_vm_root_gem(vm));
+       panthor_vm_unmap_range(vm, bo->va_node.start, bo->va_node.size);
        panthor_vm_free_va(vm, &bo->va_node);
        drm_gem_object_put(bo->obj);
-
-out_free_bo:
        panthor_vm_put(vm);
        kfree(bo);
 }