linux-hardening - [PATCH] drm/dp: Actually read Adjust Request Post Cursor2 register

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Date:   Fri,  3 Dec 2021 00:43:54 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Thierry Reding <treding@...dia.com>,
        Lyude Paul <lyude@...hat.com>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-hardening@...r.kernel.org
Subject: [PATCH] drm/dp: Actually read Adjust Request Post Cursor2 register

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@...omium.org>
---
 include/drm/drm_dp_helper.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 472dac376284..277643d2fe2c 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1517,7 +1517,15 @@ enum drm_dp_phy {
 #define DP_MST_LOGICAL_PORT_0 8
 
 #define DP_LINK_CONSTANT_N_VALUE 0x8000
-#define DP_LINK_STATUS_SIZE	   6
+/*
+ * DPCD registers in link_status:
+ * Link Status:		0x202 through 0x204
+ * Sink Status:		0x205
+ * Adjust Request:	0x206 through 0x207
+ * Training Score:	0x208 through 0x20b
+ * AR Post Cursor2:	0x20c
+ */
+#define DP_LINK_STATUS_SIZE	   11
 bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
 			  int lane_count);
 bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
-- 
2.30.2