[tip: x86/core] x86/ftrace: Rebalance RSB

tip-bot2 for Peter Zijlstra
2022-10-17T14:54:07Z

The following commit has been merged into the x86/core branch of tip:

Commit-ID: 36b64f101219dd9e6e4f0ea880b64e8a90da547b
Gitweb: https://git.kernel.org/tip/36b64f101219dd9e6e4f0ea880b64e8a90da547b
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 15 Sep 2022 13:11:36 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 17 Oct 2022 16:41:19 +02:00

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
---
arch/x86/kernel/ftrace_64.S | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index a90c55a..b5b54f5 100644
--- 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)