linux-kernel - [PATCH -tip v8 09/13] kprobes: Enable stacktrace from pt

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Message-Id: <162400000592.506599.4695807810528866713.stgit@devnote2>
Date:   Fri, 18 Jun 2021 16:06:46 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>
Cc:     X86 ML <x86@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kuba@...nel.org, mingo@...hat.com,
        ast@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>, kernel-team@...com,
        yhs@...com, linux-ia64@...r.kernel.org,
        Abhishek Sagar <sagar.abhishek@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: [PATCH -tip v8 09/13] kprobes: Enable stacktrace from pt_regs in kretprobe handler

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).

Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Tested-by: Andrii Nakryik <andrii@...nel.org>
---
 Changes in v8:
  - Update comment to clarify why this is needed.
 Changes in v3:
  - Cast the correct_ret_addr to unsigned long.
---
 kernel/kprobes.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 650cbe738666..ba729ed05cb3 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1896,6 +1896,9 @@ unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
 		BUG_ON(1);
 	}
 
+	/* Set the instruction pointer to the correct address */
+	instruction_pointer_set(regs, (unsigned long)correct_ret_addr);
+
 	/* Run them. */
 	first = current->kretprobe_instances.first;
 	while (first) {