Re: [PATCH v2 18/39] x86/ibt: Add IBT feature, MSR and #CP handling

[Peter Zijlstra]

On Tue, Mar 01, 2022 at 04:14:42PM +0100, Peter Zijlstra wrote:

> Something like so?
> 
> diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> index 399f075ccdc4..5b65f6ec5ee6 100644
> --- a/arch/x86/kernel/relocate_kernel_64.S
> +++ b/arch/x86/kernel/relocate_kernel_64.S
> @@ -114,6 +114,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
>  	/* store the start address on the stack */
>  	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

I *think* it worked, I 'apt install kexec-tools' and copied the magic
commands Josh gave over IRC and the machine went and came back real
quick.

Lacking useful console I can't say much more.

I pushed out a version with these things on.