On Fri, Dec 03, 2021 at 01:25:17AM -0800, Kees Cook wrote:
> The link_status array was not large enough to read the Adjust Request
> Post Cursor2 register. Adjust the size to include it. Found with a
> -Warray-bounds build:
> 
> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor':
> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds]
>    59 |         return link_status[r - DP_LANE0_1_STATUS];
>       |                ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status'
>   147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
>       |                                          ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v2: Fix missed array size change in intel_dp_check_mst_status()
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c |  8 ++++----
>  include/drm/drm_dp_helper.h             | 10 +++++++++-
>  2 files changed, 13 insertions(+), 5 deletions(-)

This sounds very familiar and I vaguely recall typing up a patch like
that a long time ago. But I obviously failed because that never seems
to have made it upstream.

Or perhaps I'm misremembering and was thinking about this instead:

	https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/338590/

Bonus points for adding that comment with background information on why
we need this.

Reviewed-by: Thierry Reding <treding@nvidia.com>