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Date: Fri, 25 Sep 2015 08:15:23 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Dave Hansen <dave@sr71.net>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Kees Cook <keescook@google.com>
Subject: Re: [PATCH 26/26] x86, pkeys: Documentation
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* Dave Hansen <dave@sr71.net> wrote:

> > I.e. AFAICS pkeys could be used to create true '--x' permissions for executable 
> > (user-space) pages.
> 
> Just remember that all of the protections are dependent on the contents of PKRU.  
> If an attacker controls the Access-Disable bit in PKRU for the executable-only 
> region, you're sunk.

The same is true if the attacker can execute mprotect() calls.

> But, that either requires being able to construct and execute arbitrary code 
> *or* call existing code that sets PKRU to the desired values. Which, I guess, 
> gets harder to do if all of the the wrpkru's are *in* the execute-only area.

Exactly. True --x executable regions makes it harder to 'upgrade' limited attacks.

Thanks,

	Ingo