[0/2] Fix purging buffers in the shmem helpers

Message

Neil Roberts Feb. 23, 2021, 3:51 p.m. UTC

These two patches fix a problem with the madvise purging code for the
shmem helpers where the mmaping for a purged buffer wouldn't get
invalidated correctly. This presumably ends up as a security hole
where the mapping can be accessed from user-space to read and write
random pages from other buffers. This is currently affecting Panfrost.
The second patch is a v2 from a patch that was sent standalone.

There is a WIP IGT test for Panfrost which demonstrates the bug here:

https://gitlab.freedesktop.org/nroberts/igt-gpu-tools/-/commits/panfrost-purgemap/

Neil Roberts (2):
  drm/shmem-helper: Check for purged buffers in fault handler
  drm/shmem-helper: Don't remove the offset in vm_area_struct pgoff

 drivers/gpu/drm/drm_gem_shmem_helper.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

Comments

Steven Price March 5, 2021, 10:22 a.m. UTC | #1

On 23/02/2021 15:51, Neil Roberts wrote:
> These two patches fix a problem with the madvise purging code for the
> shmem helpers where the mmaping for a purged buffer wouldn't get
> invalidated correctly. This presumably ends up as a security hole
> where the mapping can be accessed from user-space to read and write
> random pages from other buffers. This is currently affecting Panfrost.
> The second patch is a v2 from a patch that was sent standalone.
> 
> There is a WIP IGT test for Panfrost which demonstrates the bug here:
> 
> https://gitlab.freedesktop.org/nroberts/igt-gpu-tools/-/commits/panfrost-purgemap/
> 
> Neil Roberts (2):
>    drm/shmem-helper: Check for purged buffers in fault handler
>    drm/shmem-helper: Don't remove the offset in vm_area_struct pgoff
> 
>   drivers/gpu/drm/drm_gem_shmem_helper.c | 25 ++++++++++++++++++-------
>   1 file changed, 18 insertions(+), 7 deletions(-)
> 

Pushed to drm-misc-fixes

Thanks,

Steve