linux-kernel - Re: [PATCH V8 26/44] x86/fault: Print PKS MSR on fault

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Date:   Thu, 17 Feb 2022 22:01:19 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "hpa@...or.com" <hpa@...or.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 26/44] x86/fault: Print PKS MSR on fault

On Tue, Feb 01, 2022 at 10:13:40AM -0800, Edgecombe, Rick P wrote:
> On Thu, 2022-01-27 at 09:54 -0800, ira.weiny@...el.com wrote:
> > +       if (error_code & X86_PF_PK)
> > +               pks_dump_fault_info(regs);
> > +
> 
> If the kernel makes an errant accesses to a userspace address with PKU
> enabled and the usersapce page marked AD, it should oops and get here,
> but will the X86_PF_PK bit be set even if smap is the real cause? Per
> the SDM, it sounds like it would:
> "
> For accesses to user-mode addresses, the flag is set if
> (1) CR4.PKE = 1;
> (2) the linear address has protection key i; and
> (3) the PKRU register (see Section 4.6.2) is such that either
>         (a) ADi = 1; or
>         (b) the following all hold:
>                 (i) WDi = 1;
>                 (ii) the access is a write access; and
>                 (iii) either CR0.WP = 1 or the access causing the
>                       page-fault exception was a user-mode access.
> "
> 
> ...and then this somewhat confusingly dumps the pks register. Is that
> the real behavior?

Are you suggesting the PKRU should be printed instead or in addition to the
PKS?

AFAICS this really should not present a problem even if the fault is due to a
user pkey violation.  It is simply extra information.

Ira