This is a note to let you know that I've just added the patch titled
x86/xen: fix xen_hypercall_hvm() to not clobber %rbx
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-xen-fix-xen_hypercall_hvm-to-not-clobber-rbx.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 92662edb9522c377f8a707fac35e2ba2cd8b98d4
Author: Juergen Gross <jgross@xxxxxxxx>
Date: Wed Feb 5 09:43:31 2025 +0100
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 <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>
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 721a57700a3b0..ce96877c3c4fe 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
