x86/kexec: Mark relocate_kernel page as ROX instead of RWX

All writes to the page now happen before it gets marked as executable
(or after it's already switched to the identmap page tables where it's
OK to be RWX).

Signed-off-by: David Woodhouse <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: dwmw2

arch/x86/kernel/machine_kexec_64.c

@@ -323,7 +323,7 @@ int machine_kexec_prepare(struct kimage *image)
 
 	__memcpy(control_page, __relocate_kernel_start, reloc_end - reloc_start);
 
-	set_memory_x((unsigned long)control_page, 1);
+	set_memory_rox((unsigned long)control_page, 1);
 
 	return 0;
 }
@@ -333,6 +333,7 @@ void machine_kexec_cleanup(struct kimage *image)
 	void *control_page = page_address(image->control_code_page);
 
 	set_memory_nx((unsigned long)control_page, 1);
+	set_memory_rw((unsigned long)control_page, 1);
 
 	free_transition_pgtable(image);
 }