Re: [PATCH 14/14] arm64: add VMAP_STACK overflow detection

From: Mark Rutland
Date: Tue Aug 15 2017 - 07:20:27 EST


On Tue, Aug 15, 2017 at 12:10:32PM +0100, Catalin Marinas wrote:
> On Mon, Aug 07, 2017 at 07:36:05PM +0100, Mark Rutland wrote:
> > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> > index e5aa866..44a27c3 100644
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -72,6 +72,37 @@
> > .macro kernel_ventry label
> > .align 7
> > sub sp, sp, #S_FRAME_SIZE
> > +#ifdef CONFIG_VMAP_STACK
> > + add sp, sp, x0 // sp' = sp + x0
> > + sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp
> > + tbnz x0, #THREAD_SHIFT, 0f
> > + sub x0, sp, x0 // sp' - x0' = (sp + x0) - sp = x0
> > + sub sp, sp, x0 // sp' - x0 = (sp + x0) - x0 = sp
> > + b \label
>
> Maybe a small comment before this hunk just to tell the user that it's
> trying to test a bit in SP without corrupting a gpr. It's obvious once
> you read it but not you see it for the first time ;).
>
> > +
> > + /* Stash the original SP value in tpidr_el0 */
> > +0: msr tpidr_el0, x0
>
> And a comment here that on this path we no longer care about the user
> tpidr_el0 as we are never returning there.

Ok.

I've updated comments in both cases.

> Otherwise I'm fine with the series (I'm not a fan of the complexity it
> adds but I don't have a better suggestion).

Thanks!

I'll send out a v2 shortly with the changes you requested.

Thanks,
Mark.