linux-kernel - Re: [libseccomp-discuss] ARM audit, seccomp, etc are broken wrt OABI syscalls

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Date:	Wed, 6 Nov 2013 13:26:52 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Will Drewry <wad@...omium.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Eric Paris <eparis@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Richard Weinberger <richard@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	libseccomp-discuss@...ts.sourceforge.net,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [libseccomp-discuss] ARM audit, seccomp, etc are broken wrt OABI syscalls

On Wed, Nov 6, 2013 at 1:20 PM, Will Drewry <wad@...omium.org> wrote:
> On Wed, Nov 6, 2013 at 9:51 AM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
>> On Wed, Nov 06, 2013 at 10:32:31AM -0500, Eric Paris wrote:
>>> On Tue, 2013-11-05 at 14:36 -0800, Andy Lutomirski wrote:
>>> > 1. Set a different audit arch for OABI syscalls (e.g.
>>> > AUDIT_ARCH_ARMOABI).  That is, treat OABI syscall entries the same way
>>> > that x86_64 treats int 80.
>>>
>>> As the audit maintainer, I like #1.  It might break ABI, but the ABI is
>>> flat wrong now and not maintainable...
>>
>> If you read the whole thread, you will see that this corner case is just
>> not worth the effort to support.  Audit may as well be disabled by
>> kernel config if any OABI support is enabled.
>
> This might be the best move for seccomp too (as Kees suggested).  I'd
> love to have audit arch visibility, but it's not clear that it's worth
> any sort of larger changes ...
>
> ... like adding a task_thread_info.compat flag that bubbles up to
> syscall_get_arch(), or if we assume consumers of syscall_get_nr() are
> broken today (I haven't checked), then it would be possible to at
> least re-add the 0x900000 bits, if compat, before handing back the
> system call number but leave the audit arch pieces alone.

How does this look, for the seccomp part?

-Kees

diff --git a/arch/Kconfig b/arch/Kconfig
index af2cc6eabcc7..3610c2d9910f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -331,7 +331,7 @@ config HAVE_ARCH_SECCOMP_FILTER

 config SECCOMP_FILTER
        def_bool y
-       depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
+       depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET && !OABI_COMPAT
        help
          Enable tasks to build secure computing environments defined
          in terms of Berkeley Packet Filter programs which implement


-- 
Kees Cook
Chrome OS Security
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