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Date: Wed, 14 Feb 2018 11:48:38 -0800
From: Kees Cook <>
To: Laura Abbott <>
Cc: Jann Horn <>, Igor Stoppa <>, 
	Boris Lukashev <>, Christopher Lameter <>, 
	Matthew Wilcox <>, Jerome Glisse <>, 
	Michal Hocko <>, Christoph Hellwig <>, 
	linux-security-module <>, Linux-MM <>, 
	kernel list <>, 
	Kernel Hardening <>, 
	linux-arm-kernel <>
Subject: Re: arm64 physmap (was Re: [PATCH 4/6] Protectable Memory)

On Wed, Feb 14, 2018 at 11:06 AM, Laura Abbott <> 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. :)



Kees Cook
Pixel Security

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