On Thu, Dec 09, 2021 at 05:20:45PM -0500, Harry Wentland wrote: > > > On 2021-12-09 01:23, Kees Cook wrote: > > On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: > >> On Fri, 03 Dec 2021, Kees Cook <[email protected]> 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 <[email protected]> > >> > >> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 > >> published in 2014, and Tegra is the only user of > >> drm_dp_get_adjust_request_post_cursor(). > > > > I see POST_CURSOR2 is used here too: > > > > drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c > > > > Looks like we read and parse that in the admgpu driver without > using drm_dp_get_adjust_request_post_cursor.
Right, and probably that could be switched to use it, but I'm not sure what the impact of the larger link_status read is. > > I don't have a strong feeling but I liked your original > patch a bit better. I'm not sure what it means when part > of a spec is deprecated. Once a spec is written display > vendors might implement it. We should make sure that > displays like that are always handled in a sane manner. Jani, Dave, any guidance here? I'm fine with whatever, but the current code is for sure broken. ;) -Kees -- Kees Cook
