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

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Date:   Tue, 1 Feb 2022 18:13:40 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "hpa@...or.com" <hpa@...or.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC:     "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 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?