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Re: [PATCH v2] x86/mm: warn on W+x mappings

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On Wed, Oct 21, 2015 at 03:28:56PM +0200, Ard Biesheuvel wrote:
> In theory, yes. In practice, since this is supposed to be a security
> enhancement, we need some kind of ground truth to tell us which pages
> can be legally modified *and* executed, so that we can detect the
> illegal cases. My point was that, since a multitude of PE/COFF images
> can be covered by a single EfiRuntimeServicesCode region, the UEFI
> memory map does not give us enough information to make the distinction
> between a page that sits on the text/data boundary of some PE/COFF
> image and a page that sits wholly in either.

Well, we're going to simply allow the accesses to in-kernel users which
fault on those ranges, assuming that in-kernel modifiers are legit and
DTRT. Which means, we don't really need to know which pages can be
legally modified - we simply trust the in-kernel users.

The moment you're able to load an evil kernel module, guarding against
those writes is the last thing you need to worry about...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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Re: [PATCH v2] x86/mm: warn on W+x mappings Ingo Molnar <mingo@kernel.org> - 2015-10-21 11:50 +0200
  Re: [PATCH v2] x86/mm: warn on W+x mappings Ingo Molnar <mingo@kernel.org> - 2015-10-21 14:50 +0200
    Re: [PATCH v2] x86/mm: warn on W+x mappings Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-10-21 15:00 +0200
      Re: [PATCH v2] x86/mm: warn on W+x mappings Borislav Petkov <bp@alien8.de> - 2015-10-21 15:30 +0200
        Re: [PATCH v2] x86/mm: warn on W+x mappings Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-10-21 15:30 +0200
          Re: [PATCH v2] x86/mm: warn on W+x mappings Borislav Petkov <bp@alien8.de> - 2015-10-21 16:40 +0200
            Re: [PATCH v2] x86/mm: warn on W+x mappings Andy Lutomirski <luto@amacapital.net> - 2015-10-21 20:50 +0200
              Re: [PATCH v2] x86/mm: warn on W+x mappings Andy Lutomirski <luto@amacapital.net> - 2015-10-21 22:50 +0200
              Re: [PATCH v2] x86/mm: warn on W+x mappings Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-21 22:50 +0200
  Re: [PATCH v2] x86/mm: warn on W+x mappings Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-21 22:40 +0200

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