Commit 98a5cfd2 authored by Juergen Gross's avatar Juergen Gross
Browse files

x86/xen: fix xen_hypercall_hvm() to not clobber %rbx 



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: b4845bb6 ("x86/xen: add central hypercall functions")
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarJan Beulich <jbeulich@suse.com>
Reviewed-by: default avatarAndrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent bda50f77

arch/x86/xen/xen-head.S

+2 −2
Original line number Diff line number Diff line
@@ -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