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>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 0506a48f124c207c9dbe462a5b1ec7cceeea669b..bcc9948645a003f15a8779ad41e1dd3f61cfe6a3 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3039,10 +3039,13 @@ 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;