From: "Wachowski, Karol" karol.wachowski@intel.com

commit 39bc27bd688066a63e56f7f64ad34fae03fbe3b8 upstream.

Lack of check for copy-on-write (COW) mapping in drm_gem_shmem_mmap allows users to call mmap with PROT_WRITE and MAP_PRIVATE flag causing a kernel panic due to BUG_ON in vmf_insert_pfn_prot: BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));

Return -EINVAL early if COW mapping is detected.

This bug affects all drm drivers using default shmem helpers. It can be reproduced by this simple example: void *ptr = mmap(0, size, PROT_WRITE, MAP_PRIVATE, fd, mmap_offset); ptr[0] = 0;

Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects") Cc: Noralf Trønnes noralf@tronnes.org Cc: Eric Anholt eric@anholt.net Cc: Rob Herring robh@kernel.org Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@gmail.com Cc: Daniel Vetter daniel@ffwll.ch Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Wachowski, Karol karol.wachowski@intel.com Signed-off-by: Jacek Lawrynowicz jacek.lawrynowicz@linux.intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Link: https://patchwork.freedesktop.org/patch/msgid/20240520100514.925681-1-jacek.... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [Sherry: bp to fix CVE-2024-39497, ignore context change due to missing commit 21aa27ddc582 ("drm/shmem-helper: Switch to reservation lock")] Signed-off-by: Sherry Yang sherry.yang@oracle.com --- drivers/gpu/drm/drm_gem_shmem_helper.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index e33f06bb66eb..fb8093577245 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -638,6 +638,9 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct return ret; }

+ if (is_cow_mapping(vma->vm_flags)) + return -EINVAL; + ret = drm_gem_shmem_get_pages(shmem); if (ret) return ret;