6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Juergen Gross <jgross@xxxxxxxx>
[ 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 <jgross@xxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 4fd814321ed02..9ecdde17c4e1e 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
--
2.39.5
