[tip: x86/urgent] objtool/x86: Fixup frame-pointer vs rethunk

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     dbf46008775516f7f25c95b7760041c286299783
Gitweb:        https://git.kernel.org/tip/dbf46008775516f7f25c95b7760041c286299783
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Wed, 16 Aug 2023 13:59:21 +02:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Thu, 17 Aug 2023 00:44:35 +02:00

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@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230816115921.GH980931@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 tools/objtool/check.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7a9aaf4..1384090 100644
--- 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;