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@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/Ys66hwtFcGbYmoiZ@hirez.programming.kicks-ass.net/

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index d685853..62f6b8b 100644 (file)
--- 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",