linux-kernel - Re: [PATCH v3 22/39] x86/ibt: Add IBT feature, MSR and #CP handling

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Date:   Fri, 4 Mar 2022 21:39:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH v3 22/39] x86/ibt: Add IBT feature, MSR and #CP handling

On Fri, Mar 04, 2022 at 10:07:20AM -0800, Josh Poimboeuf wrote:
> On Thu, Mar 03, 2022 at 12:23:43PM +0100, Peter Zijlstra wrote:
> > @@ -310,6 +311,7 @@ void machine_kexec(struct kimage *image)
> >  	/* Interrupts aren't acceptable while we reboot */
> >  	local_irq_disable();
> >  	hw_breakpoint_disable();
> > +	cet_disable();
> >  
> >  	if (image->preserve_context) {
> >  #ifdef CONFIG_X86_IO_APIC
> > --- a/arch/x86/kernel/relocate_kernel_64.S
> > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > @@ -115,6 +115,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_ma
> >  	pushq   %rdx
> >  
> >  	/*
> > +	 * Clear X86_CR4_CET (if it was set) such that we can clear CR0_WP
> > +	 * below.
> > +	 */
> > +	movq	%cr4, %rax
> > +	andq	$~(X86_CR4_CET), %rax
> > +	movq	%rax, %cr4
> > +
> > +	/*
> >  	 * Set cr0 to a known state:
> >  	 *  - Paging enabled
> >  	 *  - Alignment check disabled
> 
> This probably belongs in a separate patch...

A x86/ibt,kexec patch has just been born...