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 cb363b507a329fe84e7d1a9ec0b12bb6eadf0d0f..6ea78612635bafc6dfcfc075424043d777ce48c0 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3521,10 +3521,13 @@ 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;