[PATCH] ARM: SECCOMP support

[Nicolas Pitre]

On Sat, 25 Sep 2010, Russell King - ARM Linux wrote:

> On Thu, Sep 23, 2010 at 05:11:36PM -0400, Nicolas Pitre wrote:
> > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> > index f05a35a..cdd0a88 100644
> > --- a/arch/arm/kernel/entry-common.S
> > +++ b/arch/arm/kernel/entry-common.S
> > @@ -314,6 +314,16 @@ ENTRY(vector_swi)
> >  	tst	ip, #_TIF_SYSCALL_TRACE		@ are we tracing syscalls?
> >  	bne	__sys_trace
> >  
> > +#ifdef CONFIG_SECCOMP
> > +	tst	ip, #_TIF_SECCOMP
> > +	beq	1f
> > +	mov	r0, scno
> > +	bl	__secure_computing	
> > +	add	r0, sp, #S_R0 + S_OFF		@ pointer to regs
> > +	ldmia	r0, {r0 - r3}			@ have to reload r0 - r3
> > +1:
> > +#endif
> 
> Why not do this before the test for TIF_SYSCALL_TRACE?  You're doing
> the same check in both paths, and x86 checks for secure computing
> before any syscall tracing stuff.

Well, for one thing, the syscall tracing has the ability to change the 
actual syscall number.  So this looked like a possible hole that could 
somehow be exploited to escape the seccomp control.  So I went with the 
safest way.


Nicolas