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

From	Dave Hansen <dave@sr71.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 31/32] x86, pkeys: execute-only support
Date	2015-12-15 01:30 +0100
Message-ID	<qFLF8-522-27@gated-at.bofh.it> (permalink)
References	(2 earlier) <qFHBw-2sR-11@gated-at.bofh.it> <qFKSJ-4sB-11@gated-at.bofh.it> <qFKSL-4sB-47@gated-at.bofh.it> <qFL2q-4xi-9@gated-at.bofh.it> <qFL2q-4xi-19@gated-at.bofh.it>
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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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[PATCH 31/32] x86, pkeys: execute-only support Dave Hansen <dave@sr71.net> - 2015-12-14 20:10 +0100
  Re: [PATCH 31/32] x86, pkeys: execute-only support Kees Cook <keescook@google.com> - 2015-12-14 21:10 +0100
    Re: [PATCH 31/32] x86, pkeys: execute-only support Kees Cook <keescook@google.com> - 2015-12-15 00:40 +0100
    Re: [PATCH 31/32] x86, pkeys: execute-only support Dave Hansen <dave@sr71.net> - 2015-12-15 00:40 +0100
      Re: [PATCH 31/32] x86, pkeys: execute-only support Andy Lutomirski <luto@amacapital.net> - 2015-12-15 00:40 +0100
        Re: [PATCH 31/32] x86, pkeys: execute-only support Kees Cook <keescook@google.com> - 2015-12-15 00:50 +0100
        Re: [PATCH 31/32] x86, pkeys: execute-only support Dave Hansen <dave@sr71.net> - 2015-12-15 00:50 +0100
          Re: [PATCH 31/32] x86, pkeys: execute-only support Andy Lutomirski <luto@amacapital.net> - 2015-12-15 00:50 +0100
            Re: [PATCH 31/32] x86, pkeys: execute-only support Dave Hansen <dave@sr71.net> - 2015-12-15 01:30 +0100

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