linux-kernel - Re: [PATCH RFC V3 8/9] x86/fault: Report the PKRS state on fault

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Date:   Tue, 13 Oct 2020 11:56:53 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     ira.weiny@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 8/9] x86/fault: Report the PKRS state on fault

> @@ -548,6 +549,11 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long ad
>  		 (error_code & X86_PF_PK)    ? "protection keys violation" :
>  					       "permissions violation");
>  
> +#ifdef CONFIG_ARCH_HAS_SUPERVISOR_PKEYS
> +	if (irq_state && (error_code & X86_PF_PK))
> +		pr_alert("PKRS: 0x%x\n", irq_state->pkrs);
> +#endif

This means everyone will see 'PKRS: 0x0', even if they're on non-PKS
hardware.  I think I'd rather have this only show PKRS when we're on
cpu_feature_enabled(PKS) hardware.

...
> @@ -1148,14 +1156,15 @@ static int fault_in_kernel_space(unsigned long address)
>   */
>  static void
>  do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
> -		   unsigned long address)
> +		   unsigned long address, irqentry_state_t *irq_state)
>  {
>  	/*
> -	 * Protection keys exceptions only happen on user pages.  We
> -	 * have no user pages in the kernel portion of the address
> -	 * space, so do not expect them here.
> +	 * If protection keys are not enabled for kernel space
> +	 * do not expect Pkey errors here.
>  	 */

Let's fix the double-negative:

	/*
	 * PF_PK is only expected on kernel addresses whenn
	 * supervisor pkeys are enabled:
	 */

> -	WARN_ON_ONCE(hw_error_code & X86_PF_PK);
> +	if (!IS_ENABLED(CONFIG_ARCH_HAS_SUPERVISOR_PKEYS) ||
> +	    !cpu_feature_enabled(X86_FEATURE_PKS))
> +		WARN_ON_ONCE(hw_error_code & X86_PF_PK);

Yeah, please stick X86_FEATURE_PKS in disabled-features so you can use
cpu_feature_enabled(X86_FEATURE_PKS) by itself here..