[PATCH 5.10 010/148] x86/xen: Support objtool vmlinux.o validation in xen-head.S

[Greg Kroah-Hartman]

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

commit f4b4bc10b0b85ec66f1a9bf5dddf475e6695b6d2 upstream.

The Xen hypercall page is filled with zeros, causing objtool to fall
through all the empty hypercall functions until it reaches a real
function, resulting in a stack state mismatch.

The build-time contents of the hypercall page don't matter because the
page gets rewritten by the hypervisor.  Make it more palatable to
objtool by making each hypervisor function a true empty function, with
nops and a return.

Cc: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lore.kernel.org/r/0883bde1d7a1fb3b6a4c952bc0200e873752f609.1611263462.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/xen/xen-head.S |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -68,8 +68,9 @@ SYM_CODE_END(asm_cpu_bringup_and_idle)
 	.balign PAGE_SIZE
 SYM_CODE_START(hypercall_page)
 	.rept (PAGE_SIZE / 32)
-		UNWIND_HINT_EMPTY
-		.skip 32
+		UNWIND_HINT_FUNC
+		.skip 31, 0x90
+		ret
 	.endr
 
 #define HYPERCALL(n) \