[PATCH -tip v8 09/13] kprobes: Enable stacktrace from pt_regs in kretprobe handler

Masami Hiramatsu
2021-06-18T07:06:46Z

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@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Andrii Nakryik <andrii@kernel.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) {