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

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Message-ID: <560DBA24.5010201@sr71.net>
Date:	Thu, 1 Oct 2015 15:56:36 -0700
From:	Dave Hansen <dave@...1.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Kees Cook <keescook@...gle.com>, Ingo Molnar <mingo@...nel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 26/26] x86, pkeys: Documentation

On 10/01/2015 03:48 PM, Linus Torvalds wrote:
> On Thu, Oct 1, 2015 at 6:33 PM, Dave Hansen <dave@...1.net> wrote:
>>
>> Here it is in a quite fugly form (well, it's not opt-in).  Init crashes
>> if I boot with this, though.
>>
>> I'll see if I can turn it in to a bit more of an opt-in and see what's
>> actually going wrong.
...
> That said, I don't understand your patch. Why check PROT_WRITE? We've
> had :"execute but not write" forever. It's "execute and not *read*"
> that is interesting.

I was thinking that almost anybody doing a PROT_WRITE|PROT_EXEC really
*is* going to write to it so they'll notice pretty fast if we completely
deny them access to it.

Also, a quick ftrace showed that most mmap() callers that set PROT_EXEC
also set PROT_READ.  I'm just assuming that folks are setting PROT_READ
but aren't _really_ going to read it, so we can safely deny them all
access other than exec.
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