linux-kernel - Re: Minor PKRU bug?

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Date:	Tue, 12 Jul 2016 15:59:54 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Minor PKRU bug?

On Tue, Jul 12, 2016 at 3:55 PM, H. Peter Anvin <hpa@...or.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