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@xxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Tested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
Changes in v9:
- Update comment to explain specifically why this is necessary.
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 | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 8f7d659eb277..e7c75725934b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1924,6 +1924,13 @@ 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) {
