[PATCH 5.10 010/130] x86/xen: Support objtool vmlinux.o validation in xen-head.S

Greg Kroah-Hartman
2022-07-12T18:44:10Z

From: Josh Poimboeuf <jpoimboe@redhat.com>

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@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/0883bde1d7a1fb3b6a4c952bc0200e873752f609.1611263462.git.jpoimboe@redhat.com
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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) \