Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test

From	Borislav Petkov <bp@alien8.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test
Date	2016-02-29 23:10 +0100
Message-ID	<r7EaS-q9-3@gated-at.bofh.it> (permalink)
References	<r7oz8-6aX-5@gated-at.bofh.it> <r7oIO-6iS-19@gated-at.bofh.it> <r7CLM-7QV-1@gated-at.bofh.it> <r7CVs-7Vn-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Feb 29, 2016 at 12:45:58PM -0800, Andy Lutomirski wrote:
> I don't think so.  Sensible user programs shouldn't set AC in the first place.

Then I'm most likely missing something: so before this patch, we did
unconditionally CLAC thus disallowing kernel access to user pages. Why
don't we need it anymore and need to pay attention only to user rFLAGS?

Especially since we do:

do_fast_syscall_32
|-> __get_user
   |-> __get_user_nocheck
      |-> __uaccess_begin which is stac()

Or are we saying, we don't need that CLAC in the beginning of
entry_SYSENTER_compat() at all because we're going to STAC anyway in
__get_user() ?

Hmmm...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

Thread

[PATCH 00/10] x86: Various SYSENTER/SYSEXIT/#DB fixes and cleanups Andy Lutomirski <luto@kernel.org> - 2016-02-29 06:40 +0100
  [PATCH 06/10] x86/traps: Clear DR6 early in do_debug and improve the comment Andy Lutomirski <luto@kernel.org> - 2016-02-29 06:40 +0100
  [PATCH 08/10] x86/entry: Only allocate space for SYSENTER_stack if needed Andy Lutomirski <luto@kernel.org> - 2016-02-29 06:40 +0100
  [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test Andy Lutomirski <luto@kernel.org> - 2016-02-29 06:40 +0100
    Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing  below the existing FLAGS test Borislav Petkov <bp@alien8.de> - 2016-02-29 21:40 +0100
      Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing  below the existing FLAGS test Andy Lutomirski <luto@amacapital.net> - 2016-02-29 21:50 +0100
        Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing  below the existing FLAGS test Borislav Petkov <bp@alien8.de> - 2016-02-29 23:10 +0100
          Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing  below the existing FLAGS test Borislav Petkov <bp@alien8.de> - 2016-02-29 23:40 +0100
          Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing  below the existing FLAGS test Brian Gerst <brgerst@gmail.com> - 2016-02-29 23:40 +0100
  Re: [PATCH 00/10] x86: Various SYSENTER/SYSEXIT/#DB fixes and cleanups Andy Lutomirski <luto@amacapital.net> - 2016-02-29 20:00 +0100

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