From 522d726824cc570e0b6bf0b3af4d5a826f1b17c5 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Wed, 5 Feb 2025 09:43:31 +0100 Subject: [PATCH] x86/xen: fix xen_hypercall_hvm() to not clobber %rbx [ Upstream commit 98a5cfd2320966f40fe049a9855f8787f0126825 ] xen_hypercall_hvm(), which is used when running as a Xen PVH guest at most only once during early boot, is clobbering %rbx. Depending on whether the caller relies on %rbx to be preserved across the call or not, this clobbering might result in an early crash of the system. This can be avoided by using an already saved register instead of %rbx. Fixes: b4845bb63838 ("x86/xen: add central hypercall functions") Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich Reviewed-by: Andrew Cooper Signed-off-by: Juergen Gross Signed-off-by: Sasha Levin --- arch/x86/xen/xen-head.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 1cf94caa7600..565708675b2f 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -110,8 +110,8 @@ SYM_FUNC_START(xen_hypercall_hvm) pop %ebx pop %eax #else - lea xen_hypercall_amd(%rip), %rbx - cmp %rax, %rbx + lea xen_hypercall_amd(%rip), %rcx + cmp %rax, %rcx #ifdef CONFIG_FRAME_POINTER pop %rax /* Dummy pop. */ #endif