From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Tue, 14 Sep 2021 23:42:12 +0900
Subject: kprobes: Enable stacktrace from pt_regs in kretprobe handler
Git-commit: df91c5bccb0c2cb868b54bd68a6ddf1fcbede6b1
Patch-mainline: v5.16-rc1
References: bsc#1193277

Since the ORC unwinder from pt_regs requires setting up regs->ip
correctly, set the correct return address to the regs->ip before
calling user kretprobe handler.

This allows the kretrprobe handler to trace stack from the
kretprobe's pt_regs by stack_trace_save_regs() (eBPF will do
this), instead of stack tracing from the handler context by
stack_trace_save() (ftrace will do this).

Link: https://lkml.kernel.org/r/163163053237.489837.4272653874525136832.stgit@devnote2

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 kernel/kprobes.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 833f07f33115..ebc587b9a346 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1937,6 +1937,13 @@ unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
 		BUG_ON(1);
 	}
 
+	/*
+	 * Set the return address as the instruction pointer, because if the
+	 * user handler calls stack_trace_save_regs() with this 'regs',
+	 * the stack trace will start from the instruction pointer.
+	 */
+	instruction_pointer_set(regs, (unsigned long)correct_ret_addr);
+
 	/* Run the user handler of the nodes. */
 	first = current->kretprobe_instances.first;
 	while (first) {