Commit 85d724df authored by David Woodhouse's avatar David Woodhouse Committed by Borislav Petkov (AMD)
Browse files

x86/kexec: Use correct swap page in swap_pages function 



The swap_pages function expects the swap page to be in %r10, but there
was no documentation to that effect. Once upon a time the setup code
used to load its value from a kernel virtual address and save it to an
address which is accessible in the identity-mapped page tables, and
*happened* to use %r10 to do so, with no comment that it was left there
on *purpose* instead of just being a scratch register. Once that was no
longer necessary, %r10 just holds whatever the kernel happened to leave
in it.

Now that the original value passed by the kernel is accessible via
%rip-relative addressing, load directly from there instead of using %r10
for it. But document the other parameters that the swap_pages function
*does* expect in registers.

Fixes: b3adabae ("x86/kexec: Drop page_list argument from relocate_kernel()")
Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250109140757.2841269-4-dwmw2@infradead.org
parent 4d5f1da9

arch/x86/kernel/relocate_kernel_64.S

+6 −2
Original line number Diff line number Diff line
@@ -264,6 +264,10 @@ SYM_CODE_END(virtual_mapped) 
	/* Do the copies */

SYM_CODE_START_LOCAL_NOALIGN(swap_pages)

	UNWIND_HINT_END_OF_STACK

	/*

	 * %rdi indirection page

	 * %r11 preserve_context

	 */

	movq	%rdi, %rcx	/* Put the indirection_page in %rcx */

	xorl	%edi, %edi

	xorl	%esi, %esi
@@ -302,7 +306,7 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages) 
	jz	.Lnoswap



	/* copy source page to swap page */

	movq	%r10, %rdi

	movq	kexec_pa_swap_page(%rip), %rdi

	movl	$512, %ecx

	rep ; movsq
@@ -314,7 +318,7 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages) 


	/* copy swap page to destination page */

	movq	%rdx, %rdi

	movq	%r10, %rsi

	movq	kexec_pa_swap_page(%rip), %rsi

.Lnoswap:

	movl	$512, %ecx

	rep ; movsq