linux-kernel - Re: mainline build failure due to 5d8c3e836fc2 ("drm/amd/display: fix array-bounds error in dc_stream_remove

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Date:   Thu, 6 Oct 2022 20:55:03 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Hamza Mahfooz <hamza.mahfooz@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: mainline build failure due to 5d8c3e836fc2 ("drm/amd/display: fix
 array-bounds error in dc_stream_remove_writeback()")

On Thu, Oct 6, 2022 at 8:39 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Thu, Oct 6, 2022 at 1:51 AM Sudip Mukherjee (Codethink)
> <sudipm.mukherjee@...il.com> wrote:
> >
> > This is only seen with gcc-11, gcc-12 builds are ok.
>
> Hmm. This seems to be some odd gcc issue.
>

<snip>

>
> The fix *MAY* be to just add a '&& i < MAX_DWB_PIPES' to that loop
> too, and then gcc will see that both i and j are always 0, and that
> the code is unreachable and not warn about it. Hmm? Can you test that?

Builds fine with the change you suggested. Here is the diff.


diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
b/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
index ae13887756bf..51571245c49a 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_stream.c
@@ -520,7 +520,7 @@ bool dc_stream_remove_writeback(struct dc *dc,
        }

        /* remove writeback info for disabled writeback pipes from stream */
-       for (i = 0, j = 0; i < stream->num_wb_info && j < MAX_DWB_PIPES; i++) {
+       for (i = 0, j = 0; i < stream->num_wb_info && j <
MAX_DWB_PIPES && i < MAX_DWB_PIPES; i++) {
                if (stream->writeback_info[i].wb_enabled) {
                        if (i != j)
                                /* trim the array */



-- 
Regards
Sudip