objtool/x86: Fixup frame-pointer vs rethunk

For stack-validation of a frame-pointer build, objtool validates that
every CALL instruction is preceded by a frame-setup. The new SRSO
return thunks violate this with their RSB stuffing trickery.

Extend the __fentry__ exception to also cover the embedded_insn case
used for this. This cures:

  vmlinux.o: warning: objtool: srso_untrain_ret+0xd: call without frame pointer save/setup

Fixes: 4ae68b26c3ab ("objtool/x86: Fix SRSO mess")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20230816115921.GH980931@hirez.programming.kicks-ass.net

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7a9aaf40087378dd111a278c9a943b8782b7f9ad..1384090530dbe3e7e0c018c833aeacdf2f95b720 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2650,12 +2650,17 @@ static int decode_sections(struct objtool_file *file)
        return 0;
 }
 
-static bool is_fentry_call(struct instruction *insn)
+static bool is_special_call(struct instruction *insn)
 {
-       if (insn->type == INSN_CALL &&
-           insn_call_dest(insn) &&
-           insn_call_dest(insn)->fentry)
-               return true;
+       if (insn->type == INSN_CALL) {
+               struct symbol *dest = insn_call_dest(insn);
+
+               if (!dest)
+                       return false;
+
+               if (dest->fentry || dest->embedded_insn)
+                       return true;
+       }
 
        return false;
 }
@@ -3656,7 +3661,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
                        if (ret)
                                return ret;
 
-                       if (opts.stackval && func && !is_fentry_call(insn) &&
+                       if (opts.stackval && func && !is_special_call(insn) &&
                            !has_valid_stack_frame(&state)) {
                                WARN_INSN(insn, "call without frame pointer save/setup");
                                return 1;