Subject: Re: [PATCH 31/32] x86, pkeys: execute-only support
To: Andy Lutomirski <luto@amacapital.net>
References: <20151214190542.39C4886D@viggo.jf.intel.com>
 <20151214190632.6A741188@viggo.jf.intel.com>
 <CAGXu5jJ5oHy11Uy4N2m1aa2A9ar9-oH_kez9jq=gM8CVSj734Q@mail.gmail.com>
 <566F52CE.6080501@sr71.net>
 <CALCETrWZbBD9vOrGn+=Qr-mKVzSKkoUbo6u7u5rpG5S0RB6v+Q@mail.gmail.com>
 <566F5444.7000302@sr71.net>
 <CALCETrXhNXx_csPnXcSaPvgY52NN8kadvd8XG8FQ3dcMfvftOg@mail.gmail.com>
Cc: Kees Cook <keescook@google.com>, LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, "x86@kernel.org" <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@linux.intel.com>
From: Dave Hansen <dave@sr71.net>
Message-ID: <566F5E42.9000009@sr71.net>
Date: Mon, 14 Dec 2015 16:26:42 -0800
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On 12/14/2015 03:47 PM, Andy Lutomirski wrote:
> On Mon, Dec 14, 2015 at 3:44 PM, Dave Hansen <dave@sr71.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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