linux-kernel - Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

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Message-ID: <CABqD9hY06gaA7T8f0Te9PFpip6ix7CcbRShWcXutxbivEZJ2og@mail.gmail.com>
Date:	Thu, 16 Feb 2012 21:53:53 -0600
From:	Will Drewry <wad@...omium.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Markus Gutschke <markus@...omium.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
	davem@...emloft.net, mingo@...hat.com, oleg@...hat.com,
	peterz@...radead.org, rdunlap@...otime.net, mcgrathr@...omium.org,
	tglx@...utronix.de, luto@....edu, serge.hallyn@...onical.com,
	djm@...drot.org, scarybeasts@...il.com, indan@....nu,
	pmoore@...hat.com, akpm@...ux-foundation.org, corbet@....net,
	eric.dumazet@...il.com, keescook@...omium.org
Subject: Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

On Thu, Feb 16, 2012 at 6:50 PM, Eric Paris <eparis@...hat.com> wrote:
> On Thu, 2012-02-16 at 17:00 -0600, Will Drewry wrote:
>> On Thu, Feb 16, 2012 at 4:06 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> > On 02/16/2012 01:51 PM, Will Drewry wrote:
>
>> Then syscall_namespace(current, regs) returns
>> * 0 - SYSCALL_NS_32 (for existing 32 and config_compat)
>> * 1 - SYSCALL_NS_64 (for existing 64 bit)
>> * 2 - SYSCALL_NS_X32 (everything after 2 is arch specific)
>> * ..
>>
>> This patch series is pegged to x86 right now, so it's not a big deal
>> to add a simple syscall_namespace to asm/syscall.h.  Of course, the
>> code is always the easy part.  Even easier would be to only assign 0
>> and 1 in the seccomp_data for 32-bit or 64-bit, then leave the rest of
>> the u32 untouched until x32 stabilizes and the TS_COMPAT interactions
>> are sorted.
>
> I don't know if anyone cares, but include/linux/audit.h tries to expose
> this type of information so audit userspace can later piece things back
> together.  (we get this info from the syscall entry exit code so we know
> which arch it is).
>
> Not sure how x32 is hoping to expose its syscall info, but others are
> going to have the same/similar problem.

An earlier change Roland had prodded me toward was adding a
syscall_get_arch() call to asm/syscall.h which returned the
appropriate audit arch value for the current calling convention.  I
hate to suggest this, but should I go ahead and wire that up for x86
now, make it a dependency for HAVE_ARCH_SECCOMP_FILTER (and officially
part of asm/syscall.h) then let it trickle into existence?  Maybe
something like:

static inline int syscall_get_arch(struct task_struct *task, struct
pt_regs *regs)
{
#ifdef CONFIG_IA32_EMULATION
  if (task_thread_info(task)->status & TS_COMPAT)
    return AUDIT_ARCH_I386;
#endif
#ifdef CONFIG_64BIT
  return AUDIT_ARCH_X86_64;
#else
  return AUDIT_ARCH_I386;
#endif
}

There would be no other callers, though, because everywhere AUDIT_ARCH
is used it is hardcoded as appropriate.  Then when x32 comes along, it
can figure out where it belongs using tif status and/or regs.

I'm not sure what the appropriate way to add things to asm/syscall.h,
but I can certainly do a first cut in the x86 version.

thanks!
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