Re: [PATCH] x86/kexec: Only write through identity mapping of control page

[Dave Hansen]

On 12/12/24 12:11, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> 
> The virtual mapping of the control page may have been _PAGE_GLOBAL and
> thus its PTE might not have been flushed on the %cr3 switch and it might
> effectively still be read-only. Move the writes to it down into the
> identity_mapped() function where the same %rip-relative addressing will
> get the new mapping.
> 
> The stack is fine, as that's using the identity mapped address anyway.

Shouldn't we also ensure that Global entries don't bite anyone else?
Something like the completely untested attached patch?diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index e9e88c342f752..ecbd77aab1221 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -155,6 +155,8 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	 */
 	andl	$(X86_CR4_PAE | X86_CR4_LA57), %r13d
 	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %r13d), X86_FEATURE_TDX_GUEST
+	/* Invalidate Global entries from the TLB: */
+	andq	$~(X86_CR0_PGE), %r13d
 	movq	%r13, %cr4
 
 	/* Flush the TLB (needed?) */