linux-kernel - Re: arm64 physmap (was Re: [kernel-hardening] [PATCH 4/6] Protectable Memory)

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Date:   Wed, 14 Feb 2018 15:13:28 -0700
From:   Tycho Andersen <tycho@...ho.ws>
To:     Kees Cook <keescook@...omium.org>
Cc:     Laura Abbott <labbott@...hat.com>, Jann Horn <jannh@...gle.com>,
        Igor Stoppa <igor.stoppa@...wei.com>,
        Boris Lukashev <blukashev@...pervictus.com>,
        Christopher Lameter <cl@...ux.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: arm64 physmap (was Re: [kernel-hardening] [PATCH 4/6]
 Protectable Memory)

On Wed, Feb 14, 2018 at 11:48:38AM -0800, Kees Cook wrote:
> On Wed, Feb 14, 2018 at 11:06 AM, Laura Abbott <labbott@...hat.com> wrote:
> > fixed. Modules yes are not fully protected. The conclusion from past
> > experience has been that we cannot safely break down larger page sizes
> > at runtime like x86 does. We could theoretically
> > add support for fixing up the alias if PAGE_POISONING is enabled but
> > I don't know who would actually use that in production. Performance
> > is very poor at that point.
> 
> XPFO forces 4K pages on the physmap[1] for similar reasons. I have no
> doubt about performance changes, but I'd be curious to see real
> numbers. Did anyone do benchmarks on just the huge/4K change? (Without
> also the XPFO overhead?)
> 
> If this, XPFO, and PAGE_POISONING all need it, I think we have to
> start a closer investigation. :)

I haven't but it shouldn't be too hard. What benchmarks are you
thinking?

Tycho