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

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Date:   Wed, 14 Oct 2020 21:13:16 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     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>, 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

On Tue, Oct 13, 2020 at 11:56:53AM -0700, Dave Hansen wrote:
> > @@ -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.

Good catch, thanks.

> 
> ...
> > @@ -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:
> 	 */

done. thanks.

> 
> > -	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..

done.

thanks,
Ira