linux-kernel - Re: [PATCH] sh: fix syscall tracing

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Message-ID: <65bf8a3b-8213-0a67-1156-043bca545ada@physik.fu-berlin.de>
Date:   Thu, 3 Sep 2020 10:13:43 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org
Cc:     Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>,
        linux-kernel@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH] sh: fix syscall tracing

Hi Rich!

On 9/3/20 7:48 AM, Rich Felker wrote:
> Addition of SECCOMP_FILTER exposed a longstanding bug in
> do_syscall_trace_enter, whereby r0 (the 5th argument register) was
> mistakenly used where r3 (syscall_nr) was intended. By overwriting r0
> rather than r3 with -1 when attempting to block a syscall, the
> existing code would instead have caused the syscall to execute with an
> argument clobbered.
> 
> Commit 0bb605c2c7f2b4b3 then introduced skipping of the syscall when
> do_syscall_trace_enter returns -1, so that the return value set by
> seccomp filters would not be clobbered by -ENOSYS. This eliminated the
> clobbering of the 5th argument register, but instead caused syscalls
> made with a 5th argument of -1 to be misinterpreted as a request by
> do_syscall_trace_enter to suppress the syscall.
> 
> Fixes: 0bb605c2c7f2b4b3 ("sh: Add SECCOMP_FILTER")
> Fixes: ab99c733ae73cce3 ("sh: Make syscall tracer use tracehook notifiers, add TIF_NOTIFY_RESUME.")
> Signed-off-by: Rich Felker <dalias@...c.org>

I'm testing this patch now with a rebased kernel and a rebased libseccomp with my
patch for SuperH support on top.

I'll report back later.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@...ian.org
`. `'   Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
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