ARM: Recover kretprobe modified return address in stacktrace

Since the kretprobe replaces the function return address with
the kretprobe_trampoline on the stack, arm unwinder shows it
instead of the correct return address.

This finds the correct return address from the per-task
kretprobe_instances list and verify it is in between the
caller fp and callee fp.

Note that this supports both GCC and clang if CONFIG_FRAME_POINTER=y
and CONFIG_ARM_UNWIND=n. For the ARM unwinder, this is still
not working correctly.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

arch/arm/kernel/stacktrace.c

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 #include <linux/export.h>
+#include <linux/kprobes.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/stacktrace.h>
@@ -65,6 +66,11 @@ int notrace unwind_frame(struct stackframe *frame)
 	frame->sp = *(unsigned long *)(fp - 8);
 	frame->pc = *(unsigned long *)(fp - 4);
 #endif
+#ifdef CONFIG_KRETPROBES
+	if (is_kretprobe_trampoline(frame->pc))
+		frame->pc = kretprobe_find_ret_addr(frame->tsk,
+					(void *)frame->fp, &frame->kr_cur);
+#endif
 
 	return 0;
 }
@@ -156,6 +162,10 @@ static noinline void __save_stack_trace(struct task_struct *tsk,
 		frame.lr = (unsigned long)__builtin_return_address(0);
 		frame.pc = (unsigned long)__save_stack_trace;
 	}
+#ifdef CONFIG_KRETPROBES
+	frame.kr_cur = NULL;
+	frame.tsk = tsk;
+#endif
 
 	walk_stackframe(&frame, save_trace, &data);
 }
@@ -173,6 +183,10 @@ void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 	frame.sp = regs->ARM_sp;
 	frame.lr = regs->ARM_lr;
 	frame.pc = regs->ARM_pc;
+#ifdef CONFIG_KRETPROBES
+	frame.kr_cur = NULL;
+	frame.tsk = current;
+#endif
 
 	walk_stackframe(&frame, save_trace, &data);
 }