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Sender: Guenter Roeck <groeck7@gmail.com>
Date:   Thu, 6 Oct 2022 10:23:37 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Hamza Mahfooz <hamza.mahfooz@amd.com>
Cc:     linux-kernel@vger.kernel.org,
        Harry Wentland <harry.wentland@amd.com>,
        Leo Li <sunpeng.li@amd.com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        "Lee, Alvin" <Alvin.Lee2@amd.com>, Alex Hung <alex.hung@amd.com>,
        Pavle Kotarac <Pavle.Kotarac@amd.com>,
        Stylon Wang <stylon.wang@amd.com>,
        Aurabindo Pillai <aurabindo.pillai@amd.com>,
        "Leo (Hanghong) Ma" <hanghong.ma@amd.com>,
        Hersen Wu <hersenwu@amd.com>, Paul Hsieh <paul.hsieh@amd.com>,
        Jimmy Kizito <Jimmy.Kizito@amd.com>,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        regressions@lists.linux.dev
Subject: Re: [PATCH] drm/amd/display: fix array-bounds error in
 dc_stream_remove_writeback()
Message-ID: <20221006172337.GA753466@roeck-us.net>
References: <20220927191200.216488-1-hamza.mahfooz@amd.com>
 <20221006064615.GA2817657@roeck-us.net>
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On Wed, Oct 05, 2022 at 11:46:15PM -0700, Guenter Roeck wrote:
> On Tue, Sep 27, 2022 at 03:12:00PM -0400, Hamza Mahfooz wrote:
> > Address the following error:
> > drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c: In function ‘dc_stream_remove_writeback’:
> > drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c:527:55: error: array subscript [0, 0] is outside array bounds of ‘struct dc_writeback_info[1]’ [-Werror=array-bounds]
> >   527 |                                 stream->writeback_info[j] = stream->writeback_info[i];
> >       |                                 ~~~~~~~~~~~~~~~~~~~~~~^~~
> > In file included from ./drivers/gpu/drm/amd/amdgpu/../display/dc/dc.h:1269,
> >                  from ./drivers/gpu/drm/amd/amdgpu/../display/dc/inc/core_types.h:29,
> >                  from ./drivers/gpu/drm/amd/amdgpu/../display/dc/basics/dc_common.h:29,
> >                  from drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c:27:
> > ./drivers/gpu/drm/amd/amdgpu/../display/dc/dc_stream.h:241:34: note: while referencing ‘writeback_info’
> >   241 |         struct dc_writeback_info writeback_info[MAX_DWB_PIPES];
> >       |
> > 
> > Currently, we aren't checking to see if j remains within
> > writeback_info[]'s bounds. So, add a check to make sure that we aren't
> > overflowing the buffer.
> > 
> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
> 
> With gcc 11.3, this patch doesn't fix a problem, it introduces one.
> 
> Building csky:allmodconfig ... failed
> --------------
> Error log:
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c: In function 'dc_stream_remove_writeback':
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c:527:83: error: array subscript 1 is above array bounds of 'struct dc_writeback_info[1]' [-Werror=array-bounds]
>   527 |                                 stream->writeback_info[j] = stream->writeback_info[i];
> 
> Building mips:allmodconfig ... failed
> --------------
> Error log:
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c: In function 'dc_stream_remove_writeback':
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c:527:83: error: array subscript [0, 0] is outside array bounds of 'struct dc_writeback_info[1]' [-Werror=array-bounds]
>   527 |                                 stream->writeback_info[j] = stream->writeback_info[i];
> 
> Building arm:allmodconfig ... failed
> --------------
> Error log:
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c: In function 'dc_stream_remove_writeback':
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c:527:83: error: array subscript [0, 0] is outside array bounds of 'struct dc_writeback_info[1]' [-Werror=array-bounds]
>   527 |                                 stream->writeback_info[j] = stream->writeback_info[i];
> 

#regzbot introduced: 5d8c3e836fc2

Complete list of build failures in my test system due to this patch,
observed when building with gcc 11.3:

Build results:
	total: 149 pass: 131 fail: 18
Failed builds:
	alpha:allmodconfig
	arm:allmodconfig
	arm64:allmodconfig
	csky:allmodconfig
	i386:allyesconfig
	i386:allmodconfig
	mips:allmodconfig
	openrisc:allmodconfig
	parisc:allmodconfig
	powerpc:allmodconfig
	powerpc:ppc32_allmodconfig
	riscv32:allmodconfig
	riscv:allmodconfig
	s390:allmodconfig
	sparc64:allmodconfig
	x86_64:allyesconfig
	x86_64:allmodconfig
	xtensa:allmodconfig

Guenter