diff mbox series

[v2,1/3] x86/xen: fix xen_hypercall_hvm() to not clobber %rbx

Message ID 20250205110651.26280-2-jgross@suse.com (mailing list archive)
State Accepted
Commit 98a5cfd2320966f40fe049a9855f8787f0126825
Headers show
Series x86/xen: some xen_hypercall_hvm() fixes | expand

Commit Message

Juergen Gross Feb. 5, 2025, 11:06 a.m. UTC 
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 <jgross@suse.com>
---
V2:
- use %rcx instead of %rbx, keeping the lea instruction (Jan Beulich)
---
 arch/x86/xen/xen-head.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 9252652afe59..72f28d66e0e5 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -117,8 +117,8 @@  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