linux-kernel - [PATCH 5.15 186/201] x86/alternative: Report missing return thunk details

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Message-Id: <20220727161035.480770452@linuxfoundation.org>
Date:   Wed, 27 Jul 2022 18:11:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH 5.15 186/201] x86/alternative: Report missing return thunk details

From: Kees Cook <keescook@...omium.org>

commit 65cdf0d623bedf0e069bb64ed52e8bb20105e2ba upstream.

Debugging missing return thunks is easier if we can see where they're
happening.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/lkml/Ys66hwtFcGbYmoiZ@hirez.programming.kicks-ass.net/
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/alternative.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -554,7 +554,9 @@ void __init_or_module noinline apply_ret
 			dest = addr + insn.length + insn.immediate.value;
 
 		if (__static_call_fixup(addr, op, dest) ||
-		    WARN_ON_ONCE(dest != &__x86_return_thunk))
+		    WARN_ONCE(dest != &__x86_return_thunk,
+			      "missing return thunk: %pS-%pS: %*ph",
+			      addr, dest, 5, addr))
 			continue;
 
 		DPRINTK("return thunk at: %pS (%px) len: %d to: %pS",