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

[Borislav Petkov <bp@alien8.de>]

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.