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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id i185sm5416946pfg.80.2021.12.08.21.54.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Dec 2021 21:54:21 -0800 (PST) Date: Wed, 8 Dec 2021 21:54:20 -0800 From: Kees Cook To: Jani Nikula Cc: Maarten Lankhorst , David Airlie , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, dri-devel@lists.freedesktop.org, Thomas Zimmermann , Thierry Reding Subject: Re: [PATCH] drm/dp: Actually read Adjust Request Post Cursor2 register Message-ID: <202112082143.3BE8ABAE@keescook> References: <20211203084354.3105253-1-keescook@chromium.org> <87o85r4a4f.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87o85r4a4f.fsf@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: > On Fri, 03 Dec 2021, 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 > > 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(). > > Instead of bumping the link status read size from 6 to 11 for all > drivers I'd much rather see some other (maybe Tegra specific) solution > to this. Hmmm... Well given this is currently non-functional on Tegra (and is an OOB memory read), how about just removing it entirely? 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..bb5bfa93950f 100644 --- a/drivers/gpu/drm/tegra/dp.c +++ b/drivers/gpu/drm/tegra/dp.c @@ -559,8 +559,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, drm_dp_get_adjust_request_pre_emphasis(status, i) >> DP_TRAIN_PRE_EMPHASIS_SHIFT; - adjust->post_cursor[i] = - drm_dp_get_adjust_request_post_cursor(status, i); + adjust->post_cursor[i] = 0; } } 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 Or maybe do a long link status read in Tegra only? -- Kees Cook