1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Stack tracing support
  4 *
  5 * Copyright (C) 2012 ARM Ltd.
  6 */
  7#include <linux/kernel.h>
  8#include <linux/export.h>
  9#include <linux/ftrace.h>
 10#include <linux/kprobes.h>
 11#include <linux/sched.h>
 12#include <linux/sched/debug.h>
 13#include <linux/sched/task_stack.h>
 14#include <linux/stacktrace.h>
 15
 16#include <asm/irq.h>
 17#include <asm/stack_pointer.h>
 18#include <asm/stacktrace.h>
 19
 20/*
 21 * AArch64 PCS assigns the frame pointer to x29.
 22 *
 23 * A simple function prologue looks like this:
 24 * 	sub	sp, sp, #0x10
 25 *   	stp	x29, x30, [sp]
 26 *	mov	x29, sp
 27 *
 28 * A simple function epilogue looks like this:
 29 *	mov	sp, x29
 30 *	ldp	x29, x30, [sp]
 31 *	add	sp, sp, #0x10
 32 */
 33
 34/*
 35 * Unwind from one frame record (A) to the next frame record (B).
 36 *
 37 * We terminate early if the location of B indicates a malformed chain of frame
 38 * records (e.g. a cycle), determined based on the location and fp value of A
 39 * and the location (but not the fp value) of B.
 40 */
 41int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 42{
 43	unsigned long fp = frame->fp;
 44	struct stack_info info;
 45
 46	if (fp & 0xf)
 47		return -EINVAL;
 48
 49	if (!tsk)
 50		tsk = current;
 51
 52	if (!on_accessible_stack(tsk, fp, &info))
 53		return -EINVAL;
 54
 55	if (test_bit(info.type, frame->stacks_done))
 56		return -EINVAL;
 57
 58	/*
 59	 * As stacks grow downward, any valid record on the same stack must be
 60	 * at a strictly higher address than the prior record.
 61	 *
 62	 * Stacks can nest in several valid orders, e.g.
 63	 *
 64	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
 65	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
 66	 *
 67	 * ... but the nesting itself is strict. Once we transition from one
 68	 * stack to another, it's never valid to unwind back to that first
 69	 * stack.
 70	 */
 71	if (info.type == frame->prev_type) {
 72		if (fp <= frame->prev_fp)
 73			return -EINVAL;
 74	} else {
 75		set_bit(frame->prev_type, frame->stacks_done);
 76	}
 77
 78	/*
 79	 * Record this frame record's values and location. The prev_fp and
 80	 * prev_type are only meaningful to the next unwind_frame() invocation.
 81	 */
 82	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 83	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
 84	frame->prev_fp = fp;
 85	frame->prev_type = info.type;
 86
 87#ifdef CONFIG_FUNCTION_GRAPH_TRACER
 88	if (tsk->ret_stack &&
 89			(frame->pc == (unsigned long)return_to_handler)) {
 90		struct ftrace_ret_stack *ret_stack;
 91		/*
 92		 * This is a case where function graph tracer has
 93		 * modified a return address (LR) in a stack frame
 94		 * to hook a function return.
 95		 * So replace it to an original value.
 96		 */
 97		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
 98		if (WARN_ON_ONCE(!ret_stack))
 99			return -EINVAL;
100		frame->pc = ret_stack->ret;
101	}
102#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
103
104	/*
105	 * Frames created upon entry from EL0 have NULL FP and PC values, so
106	 * don't bother reporting these. Frames created by __noreturn functions
107	 * might have a valid FP even if PC is bogus, so only terminate where
108	 * both are NULL.
109	 */
110	if (!frame->fp && !frame->pc)
111		return -EINVAL;
112
113	return 0;
114}
115NOKPROBE_SYMBOL(unwind_frame);
116
117void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
118		     int (*fn)(struct stackframe *, void *), void *data)
119{
120	while (1) {
121		int ret;
122
123		if (fn(frame, data))
124			break;
125		ret = unwind_frame(tsk, frame);
126		if (ret < 0)
127			break;
128	}
129}
130NOKPROBE_SYMBOL(walk_stackframe);
131
132#ifdef CONFIG_STACKTRACE
133struct stack_trace_data {
134	struct stack_trace *trace;
135	unsigned int no_sched_functions;
136	unsigned int skip;
137};
138
139static int save_trace(struct stackframe *frame, void *d)
140{
141	struct stack_trace_data *data = d;
142	struct stack_trace *trace = data->trace;
143	unsigned long addr = frame->pc;
144
145	if (data->no_sched_functions && in_sched_functions(addr))
146		return 0;
147	if (data->skip) {
148		data->skip--;
149		return 0;
150	}
151
152	trace->entries[trace->nr_entries++] = addr;
153
154	return trace->nr_entries >= trace->max_entries;
155}
156
157void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
158{
159	struct stack_trace_data data;
160	struct stackframe frame;
161
162	data.trace = trace;
163	data.skip = trace->skip;
164	data.no_sched_functions = 0;
165
166	start_backtrace(&frame, regs->regs[29], regs->pc);
167	walk_stackframe(current, &frame, save_trace, &data);
168}
169EXPORT_SYMBOL_GPL(save_stack_trace_regs);
170
171static noinline void __save_stack_trace(struct task_struct *tsk,
172	struct stack_trace *trace, unsigned int nosched)
173{
174	struct stack_trace_data data;
175	struct stackframe frame;
176
177	if (!try_get_task_stack(tsk))
178		return;
179
180	data.trace = trace;
181	data.skip = trace->skip;
182	data.no_sched_functions = nosched;
183
184	if (tsk != current) {
185		start_backtrace(&frame, thread_saved_fp(tsk),
186				thread_saved_pc(tsk));
187	} else {
188		/* We don't want this function nor the caller */
189		data.skip += 2;
190		start_backtrace(&frame,
191				(unsigned long)__builtin_frame_address(0),
192				(unsigned long)__save_stack_trace);
193	}
194
195	walk_stackframe(tsk, &frame, save_trace, &data);
196
197	put_task_stack(tsk);
198}
199EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
200
201void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
202{
203	__save_stack_trace(tsk, trace, 1);
204}
205
206void save_stack_trace(struct stack_trace *trace)
207{
208	__save_stack_trace(current, trace, 0);
209}
210
211EXPORT_SYMBOL_GPL(save_stack_trace);
212#endif