linux-kernel - Re: [libseccomp-discuss] Making a universal list of syscalls?

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Date:	Thu, 27 Feb 2014 16:16:29 -0500
From:	Paul Moore <pmoore@...hat.com>
To:	libseccomp-discuss@...ts.sourceforge.net,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>
Cc:	Andy Lutomirski <luto@...capital.net>
Subject: Re: [libseccomp-discuss] Making a universal list of syscalls?

On Thursday, February 27, 2014 12:40:32 PM Andy Lutomirski wrote:
> Currently, dealing with Linux syscalls in an architecture-independent
> way is a mess.  Here are some issues:
> 
>  1. There's no clean way to map between syscall names and numbers on
> different architectures.  The kernel contains a number of tables (that
> work differently for different architectures).  strace has some arcane
> mechanism.  libseccomp has another.

This is a major pain point for libseccomp, what we have now is passable, and 
it works, but I cringe each time I look at it because I worry about 
maintaining it.  I would be very happy if the kernel had some 
header/file/whatever that could be used by userspace applications to map 
syscall names/numbers for each architecture.

>  2. There's no clean way to map between syscall argument registers and
> logical syscall arguments.  Each architecture knows how to do it, as
> do strace and glibc, but I suspect that *everyone* else gets it wrong.
>  Especially on ARM.

I remember looking into this with libseccomp, around the ARM time frame with 
Andy, and I believe I managed to reassure myself - not well, mind you - that 
we were *ok* with seccomp/libseccomp.  However, having a argument mapping 
document/header/etc. would go a long way here.

>  3. Determining which architectures have which syscalls is a mess.
> Recent kernel builds love to warn me that finit_module is missing on
> x86_64.  This is simply not true.  I have no idea why.

Closely related to item #1.  Also a major pain for libseccomp for the same 
reasons.

>  5. Decoding ucontext from SIGSYS is a mess.  I have prototype code
> for libseccomp that can do it, but it gets the arguments wrong due to
> ABI issues.  See (2).

I've actually been sitting on some of Andy's libseccomp code for this for a 
while now because the solution is very fiddly.  Improvements here could make 
life much easier for us and remove a lot of my hesitation in merging Andy's 
code.

-- 
paul moore
security and virtualization @ redhat

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