From 1c50e8da50b07c69385d601dd0443f5bbe71d933 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Fri, 29 Nov 2024 15:47:49 +0100
Subject: [PATCH] objtool/x86: allow syscall instruction

commit dda014ba59331dee4f3b773a020e109932f4bd24 upstream.

The syscall instruction is used in Xen PV mode for doing hypercalls.
Allow syscall to be used in the kernel in case it is tagged with an
unwind hint for objtool.

This is part of XSA-466 / CVE-2024-53241.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Co-developed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 tools/objtool/check.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index fd6714de2260..c2596b1e1fb1 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3206,10 +3206,13 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			break;
 
 		case INSN_CONTEXT_SWITCH:
-			if (func && (!next_insn || !next_insn->hint)) {
-				WARN_FUNC("unsupported instruction in callable function",
-					  sec, insn->offset);
-				return 1;
+			if (func) {
+				if (!next_insn || !next_insn->hint) {
+					WARN_FUNC("unsupported instruction in callable function",
+						  sec, insn->offset);
+					return 1;
+				}
+				break;
 			}
 			return 0;