[PATCH 5.10 134/135] objtool/x86: Fixup frame-pointer vs rethunk

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5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit dbf46008775516f7f25c95b7760041c286299783 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 tools/objtool/check.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2079,12 +2079,17 @@ static int decode_sections(struct objtoo
 	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->call_dest->fentry)
-		return true;
+	if (insn->type == INSN_CALL) {
+		struct symbol *dest = insn->call_dest;
+
+		if (!dest)
+			return false;
+
+		if (dest->fentry)
+			return true;
+	}
 
 	return false;
 }
@@ -2958,7 +2963,7 @@ static int validate_branch(struct objtoo
 			if (ret)
 				return ret;
 
-			if (!no_fp && func && !is_fentry_call(insn) &&
+			if (!no_fp && func && !is_special_call(insn) &&
 			    !has_valid_stack_frame(&state)) {
 				WARN_FUNC("call without frame pointer save/setup",
 					  sec, insn->offset);





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