linux-kernel - Re: [PATCH] x86/pkeys: Explicitly treat PK #PF on kernel address as a bad area

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Message-ID: <356b4517-3c09-2bfa-a105-82bba3f1c4ff@intel.com>
Date:   Thu, 30 Aug 2018 16:33:43 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH] x86/pkeys: Explicitly treat PK #PF on kernel address as a
 bad area

On 08/30/2018 03:40 AM, Thomas Gleixner wrote:
> Given the time span you should be close to ground water with your digging
> by now.

So, turns out that we start our spurious_fault() code with this check:

>         if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
>             error_code != (X86_PF_INSTR | X86_PF_PROT))
>                 return 0;

Which ensures that we only do spurious checking for *very* specific
error_code's.  That ends up making the X86_PF_PK check inside of
spurious_fault_check() dead code _anyway_.  It's totally unreachable as
far as I can tell.

We could add a comment above the error_code check to make it explicit
that it excludes pkeys.

But, otherwise, I think we can just axe the X86_PF_PK
spurious_fault_check().