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

[Kees Cook]

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

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/Ys66hwtFcGbYmoiZ@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 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