objtool: Fix INSN_CONTEXT_SWITCH handling in validate_unret()

The !CONFIG_IA32_EMULATION version of xen_entry_SYSCALL_compat() ends
with a SYSCALL instruction which is classified by objtool as
INSN_CONTEXT_SWITCH.

Unlike validate_branch(), validate_unret() doesn't consider
INSN_CONTEXT_SWITCH in a non-function to be a dead end, so it keeps
going past the end of xen_entry_SYSCALL_compat(), resulting in the
following warning:

  vmlinux.o: warning: objtool: xen_reschedule_interrupt+0x2a: RET before UNTRAIN

Fix that by adding INSN_CONTEXT_SWITCH handling to validate_unret() to
match what validate_branch() is already doing.

Fixes: a09a6e2399ba ("objtool: Add entry UNRET validation")
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/f5eda46fd09f15b1f5cde3d9ae3b92b958342add.1744095216.git.jpoimboe@kernel.org

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4a1f6c3169b3b6fb02c35759d79c3c8b86cf6db7..c81b070ca4952f38b9c4a8ab2b7e2ffb9ab02329 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3886,6 +3886,11 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
                        WARN_INSN(insn, "RET before UNTRAIN");
                        return 1;
 
+               case INSN_CONTEXT_SWITCH:
+                       if (insn_func(insn))
+                               break;
+                       return 0;
+
                case INSN_NOP:
                        if (insn->retpoline_safe)
                                return 0;