linux-kernel - Re: [PATCH 26/26] x86, pkeys: Documentation

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Date:	Fri, 25 Sep 2015 08:15:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Dave Hansen <dave@...1.net>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>, Kees Cook <keescook@...gle.com>
Subject: Re: [PATCH 26/26] x86, pkeys: Documentation


* Dave Hansen <dave@...1.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
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