linux-kernel - Re: [PATCH 2/2] arm64: Clear the stack

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Date:   Mon, 14 May 2018 15:07:15 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Alexander Popov <alex.popov@...ux.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: Clear the stack

On Mon, May 14, 2018 at 04:53:12PM +0300, Alexander Popov wrote:
> On 14.05.2018 13:06, Mark Rutland wrote:
> > I think it is reasonable to panic() here even with CONFIG_VMAP_STACK
> > selected.
> 
> It's too tough for CONFIG_VMAP_STACK on x86 - the system can proceed to live.
> Anyway, the check_alloca() code will not be shared between x86 and arm64, I've
> described the reasons in this thread. So I can have BUG() for CONFIG_VMAP_STACK
> on x86 and Laura can consistently use panic() on arm64.

If we need arch-specific implementations anyway, then that's fine by me.

> >> So we should not do it in check_alloca() as well, just use BUG() and
> >> hope for the best.
> > 
> > Regardless of whether we BUG() or panic(), we're hoping for the best.
> > 
> > Consistently using panic() here will keep things simpler, so any failure
> > reported will be easier to reason about, and easier to debug.
> 
> Let me keep BUG() for !CONFIG_SCHED_STACK_END_CHECK. I beware of using panic()
> by default, let distro/user decide this. I remember very well how I was shouted
> at, when this one was merged:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ce6fa91b93630396ca220c33dd38ffc62686d499

Sure; my comments needn't hold up your patches.

Thanks,
Mark.