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

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Message-ID: <CADVatmMOEtX_vpR2iv9r7n5x76xjuyHwx6duERqjMutb=AKrhA@mail.gmail.com>
Date:   Thu, 6 Oct 2022 21:49:33 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.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 9:37 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Oct 06, 2022 at 12:39:40PM -0700, Linus Torvalds wrote:
> > What confuses me is that error message ("array subscript [0, 0] is
> > outside array bounds of 'struct dc_writeback_info[1]') which seems to
> > be aware that the value is actually 0.
>
> I've seen bugs in the tracker where the reporting is broken but the
> range checker is working "correctly", which seems to be the case here.
>
> > If somebody cannot come up with a fix, I suspect the solution is "gcc
> > array bounds analysis is terminally buggy" and we just need to disable
> > it for gcc-11 too.
>
> It does continue to find bugs, so I'd rather keep it on. GCC has fixed
> all the issues we've run into so far (though not all have been back
> ported to GCC 12 yet, so yes, let's keep -Warray-bounds disabled there).
>
> Specifically, I've been tracking:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105679     Fixed 13+
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578      Fixed 12+, 11.3

Thats odd, the bug report says its fixed but I am using:
gcc version 11.3.1 20220925 (GCC)

>
> And it looks like Sudip's proposed fix for this particular code is
> additionally fixing unsigned vs signed as well. I think -Warray-bounds
> did its job (though, with quite a confusing index range in the report).

Not my. Linus's. I just tested. :)


-- 
Regards
Sudip