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

[Josh Poimboeuf]

On Tue, Mar 01, 2022 at 10:02:45PM +0100, Peter Zijlstra wrote:
> 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.

I just used your latest git tree, kexec into a non-IBT kernel worked for
me as well.

-- 
Josh