x86/ftrace: Rebalance RSB

ftrace_regs_caller() uses a PUSH;RET pattern to tail-call into a
direct-call function, this unbalances the RSB, fix that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111148.823216933@infradead.org

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index a90c55a..b5b54f5 100644 (file)
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -271,6 +271,17 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
        /* Restore flags */
        popfq
        UNWIND_HINT_FUNC
+
+       /*
+        * The above left an extra return value on the stack; effectively
+        * doing a tail-call without using a register. This PUSH;RET
+        * pattern unbalances the RSB, inject a pointless CALL to rebalance.
+        */
+       ANNOTATE_INTRA_FUNCTION_CALL
+       CALL .Ldo_rebalance
+       int3
+.Ldo_rebalance:
+       add $8, %rsp
        RET
 
 SYM_FUNC_END(ftrace_regs_caller)