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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: [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
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