Date: Wed, 14 Feb 2018 11:48:38 -0800 From: Kees Cook <keescook@...omium.org> To: Laura Abbott <labbott@...hat.com> Cc: 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 11:06 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 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  http://www.openwall.com/lists/kernel-hardening/2017/09/07/13 -- Kees Cook Pixel Security
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