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Subject: Re: [PATCH 3/4] sh: Add SECCOMP_FILTER
To:     Rich Felker <dalias@libc.org>
Cc:     Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>,
        linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>
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From:   John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
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Date:   Thu, 3 Sep 2020 08:04:44 +0200
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On 9/3/20 7:46 AM, Rich Felker wrote:
> 
> OK, I think I have an explanation for the mechanism of the bug, and it
> really is a combination of the 2008 bug (confusion of r0 vs r3) and
> the SECCOMP_FILTER commit. When the syscall_trace_entry code path is
> in use, a syscall with argument 5 having value -1 causes
> do_syscall_trace_enter to return -1 (because it returns regs[0], which
> contains argument 5), which the change in entry-common.S interprets as
> a sign to skip the syscall and jump to syscall_exit, and things blow
> up from there. In particular, SYS_mmap2 is almost always called with
> -1 as the 5th argument (fd), and this is even more common on nommu
> where SYS_brk does not work.
> 
> I'll follow up with a new proposed patch.

I'm not sure whether we need another revision of your first patch. Your
previous analysis was at least right regarding the tests 51 and 58
but those have been fixed now.

But there were two other tests failing, weren't there?

I have to recheck later, I just got up (it's 8 AM CEST).

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@debian.org
`. `'   Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913