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

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Date:   Wed, 13 Jul 2022 14:38:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Song Liu <song@...nel.org>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] x86/alternative: Report missing return thunk details

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

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

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index d6858533e6e5..62f6b8b7c4a5 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -555,7 +555,9 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
 			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",
-- 
2.32.0