linux-kernel - Re: [PATCH 31/32] x86, pkeys: execute-only support

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Message-ID: <566F5E42.9000009@sr71.net>
Date:	Mon, 14 Dec 2015 16:26:42 -0800
From:	Dave Hansen <dave@...1.net>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Kees Cook <keescook@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, "x86@...nel.org" <x86@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 31/32] x86, pkeys: execute-only support

On 12/14/2015 03:47 PM, Andy Lutomirski wrote:
> On Mon, Dec 14, 2015 at 3:44 PM, Dave Hansen <dave@...1.net> wrote:
>> On 12/14/2015 03:39 PM, Andy Lutomirski wrote:
>>>>> Nope.  My linker-fu is weak.
>>>>>
>>>>> Can we even depend on the linker by itself?  Even if the sections were
>>>>> marked --x, we can't actually use them with those permissions unless we
>>>>> have protection keys.
>>>>>
>>>>> Do we need some special tag on the section to tell the linker to map it
>>>>> as --x under some conditions and r-x for others?
>>>>>
>>> Why?  Wouldn't --x just end up acting like r-x if PKRU is absent?
>>
>> An app doing --x would expect it to be unreadable.  I don't think we can
>> just silently turn it in to r-x.
> 
> I don't see why.  After all, an app doing --x right now gets rx.  An
> app doing r-- still gets r-x on some systems.

... and you're right.  I'd managed to convince myself otherwise, somehow.

Let me go see if I can get the execve() code to make one of these
mappings if I hand it properly-aligned sections.
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