[PATCH v3 57/59] x86/ftrace: Rebalance RSB

[Peter Zijlstra]

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/kernel/ftrace_64.S |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- 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,
 	/* 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)