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/pointer_auth.h>
 18#include <asm/stack_pointer.h>
 19#include <asm/stacktrace.h>
 20
 21/*
 22 * AArch64 PCS assigns the frame pointer to x29.
 23 *
 24 * A simple function prologue looks like this:
 25 * 	sub	sp, sp, #0x10
 26 *   	stp	x29, x30, [sp]
 27 *	mov	x29, sp
 28 *
 29 * A simple function epilogue looks like this:
 30 *	mov	sp, x29
 31 *	ldp	x29, x30, [sp]
 32 *	add	sp, sp, #0x10
 33 */
 34
 35
 36void start_backtrace(struct stackframe *frame, unsigned long fp,
 37		     unsigned long pc)
 38{
 39	frame->fp = fp;
 40	frame->pc = pc;
 41#ifdef CONFIG_FUNCTION_GRAPH_TRACER
 42	frame->graph = 0;
 43#endif
 44
 45	/*
 46	 * Prime the first unwind.
 47	 *
 48	 * In unwind_frame() we'll check that the FP points to a valid stack,
 49	 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
 50	 * treated as a transition to whichever stack that happens to be. The
 51	 * prev_fp value won't be used, but we set it to 0 such that it is
 52	 * definitely not an accessible stack address.
 53	 */
 54	bitmap_zero(frame->stacks_done, __NR_STACK_TYPES);
 55	frame->prev_fp = 0;
 56	frame->prev_type = STACK_TYPE_UNKNOWN;
 57}
 58
 59/*
 60 * Unwind from one frame record (A) to the next frame record (B).
 61 *
 62 * We terminate early if the location of B indicates a malformed chain of frame
 63 * records (e.g. a cycle), determined based on the location and fp value of A
 64 * and the location (but not the fp value) of B.
 65 */
 66int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 67{
 68	unsigned long fp = frame->fp;
 69	struct stack_info info;
 70
 71	if (!tsk)
 72		tsk = current;
 73
 74	/* Final frame; nothing to unwind */
 75	if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
 76		return -ENOENT;
 77
 78	if (fp & 0x7)
 79		return -EINVAL;
 80
 81	if (!on_accessible_stack(tsk, fp, 16, &info))
 82		return -EINVAL;
 83
 84	if (test_bit(info.type, frame->stacks_done))
 85		return -EINVAL;
 86
 87	/*
 88	 * As stacks grow downward, any valid record on the same stack must be
 89	 * at a strictly higher address than the prior record.
 90	 *
 91	 * Stacks can nest in several valid orders, e.g.
 92	 *
 93	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
 94	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
 95	 *
 96	 * ... but the nesting itself is strict. Once we transition from one
 97	 * stack to another, it's never valid to unwind back to that first
 98	 * stack.
 99	 */
100	if (info.type == frame->prev_type) {
101		if (fp <= frame->prev_fp)
102			return -EINVAL;
103	} else {
104		set_bit(frame->prev_type, frame->stacks_done);
105	}
106
107	/*
108	 * Record this frame record's values and location. The prev_fp and
109	 * prev_type are only meaningful to the next unwind_frame() invocation.
110	 */
111	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
112	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
113	frame->prev_fp = fp;
114	frame->prev_type = info.type;
115
116#ifdef CONFIG_FUNCTION_GRAPH_TRACER
117	if (tsk->ret_stack &&
118		(ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
119		struct ftrace_ret_stack *ret_stack;
120		/*
121		 * This is a case where function graph tracer has
122		 * modified a return address (LR) in a stack frame
123		 * to hook a function return.
124		 * So replace it to an original value.
125		 */
126		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
127		if (WARN_ON_ONCE(!ret_stack))
128			return -EINVAL;
129		frame->pc = ret_stack->ret;
130	}
131#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
132
133	frame->pc = ptrauth_strip_insn_pac(frame->pc);
134
135	return 0;
136}
137NOKPROBE_SYMBOL(unwind_frame);
138
139void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
140			     bool (*fn)(void *, unsigned long), void *data)
141{
142	while (1) {
143		int ret;
144
145		if (!fn(data, frame->pc))
146			break;
147		ret = unwind_frame(tsk, frame);
148		if (ret < 0)
149			break;
150	}
151}
152NOKPROBE_SYMBOL(walk_stackframe);
153
154static void dump_backtrace_entry(unsigned long where, const char *loglvl)
155{
156	printk("%s %pSb\n", loglvl, (void *)where);
157}
158
159void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
160		    const char *loglvl)
161{
162	struct stackframe frame;
163	int skip = 0;
164
165	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
166
167	if (regs) {
168		if (user_mode(regs))
169			return;
170		skip = 1;
171	}
172
173	if (!tsk)
174		tsk = current;
175
176	if (!try_get_task_stack(tsk))
177		return;
178
179	if (tsk == current) {
180		start_backtrace(&frame,
181				(unsigned long)__builtin_frame_address(0),
182				(unsigned long)dump_backtrace);
183	} else {
184		/*
185		 * task blocked in __switch_to
186		 */
187		start_backtrace(&frame,
188				thread_saved_fp(tsk),
189				thread_saved_pc(tsk));
190	}
191
192	printk("%sCall trace:\n", loglvl);
193	do {
194		/* skip until specified stack frame */
195		if (!skip) {
196			dump_backtrace_entry(frame.pc, loglvl);
197		} else if (frame.fp == regs->regs[29]) {
198			skip = 0;
199			/*
200			 * Mostly, this is the case where this function is
201			 * called in panic/abort. As exception handler's
202			 * stack frame does not contain the corresponding pc
203			 * at which an exception has taken place, use regs->pc
204			 * instead.
205			 */
206			dump_backtrace_entry(regs->pc, loglvl);
207		}
208	} while (!unwind_frame(tsk, &frame));
209
210	put_task_stack(tsk);
211}
212
213void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
214{
215	dump_backtrace(NULL, tsk, loglvl);
216	barrier();
217}
218
219#ifdef CONFIG_STACKTRACE
220
221noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
222			      void *cookie, struct task_struct *task,
223			      struct pt_regs *regs)
224{
225	struct stackframe frame;
226
227	if (regs)
228		start_backtrace(&frame, regs->regs[29], regs->pc);
229	else if (task == current)
230		start_backtrace(&frame,
231				(unsigned long)__builtin_frame_address(1),
232				(unsigned long)__builtin_return_address(0));
233	else
234		start_backtrace(&frame, thread_saved_fp(task),
235				thread_saved_pc(task));
236
237	walk_stackframe(task, &frame, consume_entry, cookie);
238}
239
240#endif