Date: Wed, 14 Feb 2018 14:27:47 -0800 From: Kees Cook <keescook@...omium.org> To: Tycho Andersen <tycho@...ho.ws> 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 2:13 PM, Tycho Andersen <tycho@...ho.ws> wrote: > 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 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? Unless I'm looking at some specific micro benchmark, I tend to default to looking at kernel build benchmarks but that gets pretty noisy. Laura regularly uses hackbench, IIRC. I'm not finding the pastebin I had for that, though. I wonder if we need a benchmark subdirectory in tools/testing/, so we could collect some of these common tools? All benchmarks are terrible, but at least we'd have the same terrible benchmarks. :) -Kees -- Kees Cook Pixel Security
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