From a2151490cc6c57b368d7974ffd447a8b36ade639 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Thu, 24 Feb 2022 19:56:10 -0800
Subject: drm/dp: Fix OOB read when handling Post Cursor2 register
Git-commit: a2151490cc6c57b368d7974ffd447a8b36ade639
Patch-mainline: v5.18-rc1
References: bsc#1190786
The link_status array was not large enough to read the Adjust Request
Post Cursor2 register, so remove the common helper function to avoid
an OOB read, 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],
| ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Replace the only user of the helper with an open-coded fetch and decode,
similar to drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c.
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20220105173507.2420910-1-keescook@chromium.org
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
drivers/gpu/drm/tegra/dp.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
--- 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_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(
DP_TRAIN_PRE_EMPHASIS_SHIFT;
adjust->post_cursor[i] =
- drm_dp_get_adjust_request_post_cursor(status, i);
+ (post_cursor >> (i << 1)) & 0x3;
}
}