ARM audit, seccomp, etc are broken wrt OABI syscalls

[Andy Lutomirski]

On Wed, Nov 6, 2013 at 2:30 PM, Matt Sealey <neko at bakuhatsu.net> wrote:
> On Tue, Nov 5, 2013 at 6:14 PM, Kees Cook <keescook at chromium.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