linux-kernel - [PATCH] drm/amd/display: Fix logical vs bitwise bug in get_embedded_panel_info_v2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <aQSzYV0ytfQK2kvN@stanley.mountain>
Date: Fri, 31 Oct 2025 16:02:25 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Harry Wentland <harry.wentland@....com>,
	Harshit Mogalapalli <harshit.m.mogalapalli@...il.com>
Cc: Leo Li <sunpeng.li@....com>, Rodrigo Siqueira <siqueira@...lia.com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Hamish Claxton <hamishclaxton@...il.com>,
	Aurabindo Pillai <aurabindo.pillai@....com>,
	Zaeem Mohamed <zaeem.mohamed@....com>,
	Michael Strauss <michael.strauss@....com>,
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] drm/amd/display: Fix logical vs bitwise bug in
 get_embedded_panel_info_v2_1()

The .H_SYNC_POLARITY and .V_SYNC_POLARITY variables are 1 bit bitfields
of a u32.  The ATOM_HSYNC_POLARITY define is 0x2 and the
ATOM_VSYNC_POLARITY is 0x4.  When we do a bitwise negate of 0, 2, or 4
then the last bit is always 1 so this code always sets .H_SYNC_POLARITY
and .V_SYNC_POLARITY to true.

This code is instead intended to check if the ATOM_HSYNC_POLARITY or
ATOM_VSYNC_POLARITY flags are set and reverse the result.  In other
words, it's supposed to be a logical negate instead of a bitwise negate.

Fixes: ae79c310b1a6 ("drm/amd/display: Add DCE12 bios parser support")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
Please note that I have not tested this.  It's straight forward enough to
see that logical negate was intended, but it's always good to test things
as well.

Harshit and I only recently created this static checker warning.

 drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c b/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
index 04eb647acc4e..550a9f1d03f8 100644
--- a/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
+++ b/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
@@ -1480,10 +1480,10 @@ static enum bp_result get_embedded_panel_info_v2_1(
 	/* not provided by VBIOS */
 	info->lcd_timing.misc_info.HORIZONTAL_CUT_OFF = 0;
 
-	info->lcd_timing.misc_info.H_SYNC_POLARITY = ~(uint32_t) (lvds->lcd_timing.miscinfo
-			& ATOM_HSYNC_POLARITY);
-	info->lcd_timing.misc_info.V_SYNC_POLARITY = ~(uint32_t) (lvds->lcd_timing.miscinfo
-			& ATOM_VSYNC_POLARITY);
+	info->lcd_timing.misc_info.H_SYNC_POLARITY = !(lvds->lcd_timing.miscinfo &
+						       ATOM_HSYNC_POLARITY);
+	info->lcd_timing.misc_info.V_SYNC_POLARITY = !(lvds->lcd_timing.miscinfo &
+						       ATOM_VSYNC_POLARITY);
 
 	/* not provided by VBIOS */
 	info->lcd_timing.misc_info.VERTICAL_CUT_OFF = 0;
-- 
2.51.0