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Date:   Wed, 14 Feb 2018 15:13:28 -0700
From:   Tycho Andersen <tycho@tycho.ws>
To:     Kees Cook <keescook@chromium.org>
Cc:     Laura Abbott <labbott@redhat.com>, Jann Horn <jannh@google.com>,
        Igor Stoppa <igor.stoppa@huawei.com>,
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Subject: Re: arm64 physmap (was Re: [kernel-hardening] [PATCH 4/6]
 Protectable Memory)
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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@redhat.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