linux-kernel - Re: [PATCH 3.5 2/2] seccomp: Future-proof against silly tracers

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Message-ID: <CALCETrVZ2V_W-oiwPoDUrqPSv79_gMjPdH_qe+FGWyXcD64rmg@mail.gmail.com>
Date:	Thu, 2 Aug 2012 09:54:43 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Will Drewry <wad@...omium.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 3.5 2/2] seccomp: Future-proof against silly tracers

On Thu, Aug 2, 2012 at 7:32 AM, Will Drewry <wad@...omium.org> wrote:
> On Thu, Jul 26, 2012 at 10:41 AM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Tue, Jul 17, 2012 at 4:19 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>> Currently, if a tracer changes a syscall nr to __NR_future_enosys,
>>> behavior will differ between kernels that know about
>>> __NR_future_enosys (and return -ENOSYS) and older kernels (which
>>> return the value from pt_regs).  This is silly; we should just
>>> return -ENOSYS.
>>>
>>> This is unlikely to ever happen on x86 because the return value in
>>> pt_regs starts out as -ENOSYS, but a silly tracer can change that.
>>>
>>> Signed-off-by: Andy Lutomirski <luto@...capital.net>
>>> Cc: Will Drewry <wad@...omium.org>
>>> ---
>>>  arch/x86/include/asm/syscall.h |   11 +++++++++++
>>>  kernel/seccomp.c               |   15 +++++++++++++++
>>>  2 files changed, 26 insertions(+), 0 deletions(-)
>>
>> Will, can you pick this, or some version of it, up in your
>> seccomp-for-ARM tree or wherever your development is?
>
> I'm still not sure about this change though the end result is nice.
> Regardless, I'll explore it when I can -- my family has just increased
> in size, so I'm going to be a bit delayed!

I don't think there's any particular rush here.  It's a very minor ABI
change, but I had to write code to explicitly look for it to detect
any difference at all.

--Andy


>
> cheers!
> will



-- 
Andy Lutomirski
AMA Capital Management, LLC
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