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 <keescook@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> >> >> 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. 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. Harry > Here's a version of that for tegra (untested): > > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c > index 23f9073bc473..c9528aa62c9c 100644 > --- a/drivers/gpu/drm/drm_dp_helper.c > +++ b/drivers/gpu/drm/drm_dp_helper.c > @@ -144,16 +144,6 @@ u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], > } > EXPORT_SYMBOL(drm_dp_get_adjust_tx_ffe_preset); > > -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > - unsigned int lane) > -{ > - unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2; > - u8 value = dp_link_status(link_status, offset); > - > - return (value >> (lane << 1)) & 0x3; > -} > -EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor); > - > static int __8b10b_clock_recovery_delay_us(const struct drm_dp_aux *aux, u8 rd_interval) > { > if (rd_interval > 4) > diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c > index 70dfb7d1dec5..f5535eb04c6b 100644 > --- a/drivers/gpu/drm/tegra/dp.c > +++ b/drivers/gpu/drm/tegra/dp.c > @@ -549,6 +549,15 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, > { > struct drm_dp_link_train_set *adjust = &link->train.adjust; > unsigned int i; > + u8 post_cursor; > + int err; > + > + err = drm_dp_dpcd_read(link->aux, DP_ADJUST_REQUEST_POST_CURSOR2, > + &post_cursor, sizeof(post_cursor)); > + if (err < 0) { > + DRM_ERROR("failed to read post_cursor2: %d\n", err); > + post_cursor = 0; > + } > > for (i = 0; i < link->lanes; i++) { > adjust->voltage_swing[i] = > @@ -560,7 +569,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, > DP_TRAIN_PRE_EMPHASIS_SHIFT; > > adjust->post_cursor[i] = > - drm_dp_get_adjust_request_post_cursor(status, i); > + (post_cursor >> (i << 1)) & 0x3; > } > } > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h > index 30359e434c3f..28378db676c8 100644 > --- a/include/drm/drm_dp_helper.h > +++ b/include/drm/drm_dp_helper.h > @@ -1528,8 +1528,6 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI > int lane); > u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], > int lane); > -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > - unsigned int lane); > > #define DP_BRANCH_OUI_HEADER_SIZE 0xc > #define DP_RECEIVER_CAP_SIZE 0xf > > > Is that the right way to go? >