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 10:07:20 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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...

-- 
Josh