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 6604f5d038aadfff6e4465bda50662c32c9ff067..f0d8796b984a800452d0e6877a1c5252e8fe0e54 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3820,9 +3820,12 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
                        break;
 
                case INSN_CONTEXT_SWITCH:
-                       if (func && (!next_insn || !next_insn->hint)) {
-                               WARN_INSN(insn, "unsupported instruction in callable function");
-                               return 1;
+                       if (func) {
+                               if (!next_insn || !next_insn->hint) {
+                                       WARN_INSN(insn, "unsupported instruction in callable function");
+                                       return 1;
+                               }
+                               break;
                        }
                        return 0;