Re: [PATCH 3/3] arm64: kasan: clear stale stack poison

[Lorenzo Pieralisi]

On Thu, Mar 03, 2016 at 02:14:29PM +0000, Mark Rutland wrote:
> On Wed, Mar 02, 2016 at 02:26:18PM +0000, Mark Rutland wrote:
> > Functions which the compiler has instrumented for ASAN place poison on
> > the stack shadow upon entry and remove this poison prior to returning.
> > 
> > In the case of cpuidle, CPUs exit the kernel a number of levels deep
> > in C code. Any instrumented functions on this critical path will leave
> > portions of the stack shadow poisoned.
> > 
> > If CPUs lose context and return to the kernel via a cold path, we
> > restore a prior context saved in __cpu_suspend_enter are forgotten, and
> > we never remove the poison they placed in the stack shadow area by
> > functions calls between this and the actual exit of the kernel.
> > 
> > Thus, (depending on stackframe layout) subsequent calls to instrumented
> > functions may hit this stale poison, resulting in (spurious) KASAN
> > splats to the console.
> > 
> > To avoid this, clear any stale poison from the idle thread for a CPU
> > prior to bringing a CPU online.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > ---
> >  arch/arm64/kernel/sleep.S | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> > index e33fe33..fd10eb6 100644
> > --- a/arch/arm64/kernel/sleep.S
> > +++ b/arch/arm64/kernel/sleep.S
> > @@ -145,6 +145,10 @@ ENTRY(cpu_resume_mmu)
> >  ENDPROC(cpu_resume_mmu)
> >  	.popsection
> >  cpu_resume_after_mmu:
> > +#ifdef CONFIG_KASAN
> > +	mov	x0, sp
> > +	bl	kasan_unpoison_remaining_stack
> > +#endif
> 
> Lorenzo, as this was following your suggestion [1], I hope that this
> patch looks ok to you?
> 
> Are you happy to provide an Ack / Reviewed-by?

Yes sure, thanks for putting it together:

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>