From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Thu, 21 Oct 2021 09:55:00 +0900
Subject: arm64: kprobes: Make a frame pointer on __kretprobe_trampoline
Patch-mainline: v5.16-rc1
Git-commit: fc6d647638a8412800dfd10ad687709cb4aee373
References: jsc#PED-1377

Make a frame pointer (make the x29 register points the
address of pt_regs->regs[29]) on __kretprobe_trampoline.

This frame pointer will be used by the stacktracer when it is
called from the kretprobe handlers. In this case, the stack
tracer will unwind stack to trampoline_probe_handler() and
find the next frame pointer in the stack frame of the
__kretprobe_trampoline().

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 arch/arm64/kernel/probes/kprobes_trampoline.S |    4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/arm64/kernel/probes/kprobes_trampoline.S
+++ b/arch/arm64/kernel/probes/kprobes_trampoline.S
@@ -66,6 +66,9 @@ SYM_CODE_START(__kretprobe_trampoline)
 
 	save_all_base_regs
 
+	/* Setup a frame pointer. */
+	add x29, sp, #S_FP
+
 	mov x0, sp
 	bl trampoline_probe_handler
 	/*
@@ -74,6 +77,7 @@ SYM_CODE_START(__kretprobe_trampoline)
 	 */
 	mov lr, x0
 
+	/* The frame pointer (x29) is restored with other registers. */
 	restore_all_base_regs
 
 	add sp, sp, #PT_REGS_SIZE