Date: Mon, 7 Nov 2016 19:58:42 +0000 From: Ard Biesheuvel <ard.biesheuvel@...aro.org> To: Mark Rutland <mark.rutland@....com> Cc: Catalin Marinas <catalin.marinas@....com>, Laura Abbott <labbott@...hat.com>, AKASHI Takahiro <takahiro.akashi@...aro.org>, David Brown <david.brown@...aro.org>, Will Deacon <will.deacon@....com>, "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>, Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com, Matt Fleming <matt@...eblueprint.co.uk>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: Re: [PATCHv4 0/4] WX checking for arm64 On 7 November 2016 at 19:49, Mark Rutland <mark.rutland@....com> wrote: > On Mon, Nov 07, 2016 at 03:38:02PM +0000, Mark Rutland wrote: >> On Sun, Oct 30, 2016 at 03:03:07PM +0000, Catalin Marinas wrote: >> > On Thu, Oct 27, 2016 at 09:27:30AM -0700, Laura Abbott wrote: >> > > Laura Abbott (4): >> > > arm64: dump: Make ptdump debugfs a separate option >> > > arm64: dump: Make the page table dumping seq_file optional >> > > arm64: dump: Remove max_addr >> > > arm64: dump: Add checking for writable and exectuable pages >> > >> > Queued for 4.10. Thanks. >> >> Catalin mentioned to me that he saw some KASAN splats when testing; it >> looks like need a fixup something like the below. > > As an aside, it looks like any ptdump usage when KASAN is enabled takes > several minutes, which at boot time looks like a hang. > > AFAICT, this is because KASAN allocates *huge* VA ranges (4TB+) worth of > zeroed shadow memory at pte granularity (reusing the same pmd, pud, > tables), and the ptdump code dutifully walks this with, with the added > KASAN instrumentation overhead. > > I'll try to dig into that tomorrow; I suspect/hope it's not necessary to > keep all of that mapped. > I have noticed that in the past, but I see how this delay at boot time is an issue. However, I don't think there is a huge cost involved in terms of memory footprint: AFAIK, the same PMD/PTE/kasan zero page are mapped over and over across the range.
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