linux-kernel - Re: ARM audit, seccomp, etc are broken wrt OABI syscalls

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Date:	Wed, 6 Nov 2013 14:33:10 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Matt Sealey <neko@...uhatsu.net>
Cc:	Kees Cook <keescook@...omium.org>,
	Paul Moore <paul@...l-moore.com>,
	Richard Weinberger <richard@....at>,
	libseccomp-discuss@...ts.sourceforge.net,
	Will Drewry <wad@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: ARM audit, seccomp, etc are broken wrt OABI syscalls

On Wed, Nov 6, 2013 at 2:30 PM, Matt Sealey <neko@...uhatsu.net> wrote:
> On Tue, Nov 5, 2013 at 6:14 PM, Kees Cook <keescook@...omium.org> wrote:
>>
>> Alternatively, CONFIG_SECCOMP_FILTER could depend on
>> !CONFIG_OABI_COMPAT. That seems like the least work, given the desire
>> to kill OABI in the real world. (Though I would note that at least
>> Ubuntu's ARM kernels build with CONFIG_OABI_COMPAT; Chrome OS does
>> not.)
>
> I think CONFIG_OABI_COMPAT probably leaked in from the original
> configurations of the kernel taken from Debian.
>
> There were several big decisions they made (build for ARMv5 soft
> float, then switch to ARMv7 softfp, then switch to ARMv7 hardfp, then
> switch to using THUMB2 kernels) which would have just broken OABI
> binaries at every step of the way since they had some subtle
> implications in kernel configuration (note: Ubuntu have never, ever
> enabled FPA emulation in the kernel, and all Debian's OABI userspace
> is built for FPA, for example. A good chunk of the original Debian arm
> port probably would just pitch a SIGILL if you ran it under an Ubuntu
> kernel).
>
> I would ignore anyone who enables it in a distribution, since they
> probably weren't intending to enable it in the first place, and never
> noticed the.. what.. 3-4KiB it adds to the kernel?
>

Forget the size -- it adds a fair amount of complexity and a D-cache
miss on every syscall.

--Andy
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