Re: Minor PKRU bug?

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: Minor PKRU bug?
Date	2016-07-13 01:10 +0200
Message-ID	<rUeYq-3aN-5@gated-at.bofh.it> (permalink)
References	<rT7YZ-8fP-15@gated-at.bofh.it> <rU7WW-6Ps-33@gated-at.bofh.it> <rUeOK-2RS-15@gated-at.bofh.it>
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On Tue, Jul 12, 2016 at 3:55 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 07/12/16 08:32, Dave Hansen wrote:
>> On 07/09/2016 02:27 PM, Andy Lutomirski wrote:
>>> is_prefetch in arch/x86/mm/fault.c can be called on a user address
>>> that's not readable due to PKRU.  This could break it.  You might need
>>> to add a get_user_exec or similar.
>>
>> Thanks for the heads-up.  I think I'll just need a version that does
>> something along the lines of stac/clac, but with PKRU.
>>
>> I think I can do it with an "_exec" variant of probe_kernel_address(),
>> but it's a bit messy.
>>
>
> Can this particular codepath even be executed on a PKRU-equipped
> machine?  I thought it was a bug fix for a specific AMD CPU line.

It can certainly be executed -- do_sigbus will execute it every time.
But I guess it doesn't matter if it fails on a PKRU machine, because a
failure will just report the signal, and the erratum case can't happen
in the first place.

>
>         -hpa
>



-- 
Andy Lutomirski
AMA Capital Management, LLC

Thread

Re: Minor PKRU bug? Dave Hansen <dave.hansen@linux.intel.com> - 2016-07-12 17:40 +0200
  Re: Minor PKRU bug? "H. Peter Anvin" <hpa@zytor.com> - 2016-07-13 01:00 +0200
    Re: Minor PKRU bug? Dave Hansen <dave.hansen@linux.intel.com> - 2016-07-13 01:10 +0200
    Re: Minor PKRU bug? Andy Lutomirski <luto@amacapital.net> - 2016-07-13 01:10 +0200
      Re: Minor PKRU bug? Dave Hansen <dave.hansen@linux.intel.com> - 2016-07-21 23:40 +0200
        Re: Minor PKRU bug? Andy Lutomirski <luto@amacapital.net> - 2016-07-21 23:50 +0200
          Re: Minor PKRU bug? "H. Peter Anvin" <hpa@zytor.com> - 2016-07-22 00:00 +0200
            Re: Minor PKRU bug? Dave Hansen <dave.hansen@linux.intel.com> - 2016-07-22 00:30 +0200

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