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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 22 May 2023 13:41:41 +0200
Message-ID: <CAMuHMdX_0F0hSZKqBBCN3876BmfwbQb1_+N3h-V8xs5ouRXF=A@mail.gmail.com>
Subject: Re: [PATCH v1 1/1] m68k: Move signal frame following exception on 68020/030
To:     Finn Thain <fthain@linux-m68k.org>
Cc:     Michael Schmitz <schmitzmic@gmail.com>,
        Andreas Schwab <schwab@linux-m68k.org>, stable@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org
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On Sat, May 6, 2023 at 11:36 AM Finn Thain <fthain@linux-m68k.org> wrote:
> On 68030/020, an instruction such as, moveml %a2-%a3/%a5,%sp@- may cause
> a stack page fault during instruction execution (i.e. not at an
> instruction boundary) and produce a format 0xB exception frame.
>
> In this situation, the value of USP will be unreliable. If a signal is to
> be delivered following the exception, this USP value is used to calculate
> the location for a signal frame. This can result in a corrupted user
> stack.
>
> The corruption was detected in dash (actually in glibc) where it showed
> up as an intermittent "stack smashing detected" message and crash
> following signal delivery for SIGCHLD.
>
> It was hard to reproduce that failure because delivery of the signal
> raced with the page fault and because the kernel places an unpredictable
> gap of up to 7 bytes between the USP and the signal frame.
>
> A format 0xB exception frame can be produced by a bus error or an address
> error. The 68030 Users Manual says that address errors occur immediately
> upon detection during instruction prefetch. The instruction pipeline
> allows prefetch to overlap with other instructions, which means an
> address error can arise during the execution of a different instruction.
> So it seems likely that this patch may help in the address error case also.
>
> Reported-and-tested-by: Stan Johnson <userm57@yahoo.com>
> Link: https://lore.kernel.org/all/CAMuHMdW3yD22_ApemzW_6me3adq6A458u1_F0v-1EYwK_62jPA@mail.gmail.com/
> Cc: Michael Schmitz <schmitzmic@gmail.com>
> Cc: Andreas Schwab <schwab@linux-m68k.org>
> Cc: stable@vger.kernel.org
> Co-developed-by: Michael Schmitz <schmitzmic@gmail.com>
> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
> Signed-off-by: Finn Thain <fthain@linux-m68k.org>

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
i.e. will queue as a fix in the m68k for-v6.4 branch.

I plan to send this upstream later this week, so any additional
testing would be appreciated.

Thanks!

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds