1 // SPDX-License-Identifier: GPL-2.0
2
3 /*
4 * Stack trace utility functions etc.
5 *
6 * Copyright 2008 Christoph Hellwig, IBM Corp.
7 * Copyright 2018 SUSE Linux GmbH
8 * Copyright 2018 Nick Piggin, Michael Ellerman, IBM Corp.
9 */
10
11 #include <linux/export.h>
12 #include <linux/kallsyms.h>
13 #include <linux/module.h>
14 #include <linux/nmi.h>
15 #include <linux/sched.h>
16 #include <linux/sched/debug.h>
17 #include <linux/sched/task_stack.h>
18 #include <linux/stacktrace.h>
19 #include <asm/ptrace.h>
20 #include <asm/processor.h>
21 #include <linux/ftrace.h>
22 #include <asm/kprobes.h>
23
24 #include <asm/paca.h>
25
arch_stack_walk(stack_trace_consume_fn consume_entry,void * cookie,struct task_struct * task,struct pt_regs * regs)26 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
27 struct task_struct *task, struct pt_regs *regs)
28 {
29 unsigned long sp;
30
31 if (regs && !consume_entry(cookie, regs->nip))
32 return;
33
34 if (regs)
35 sp = regs->gpr[1];
36 else if (task == current)
37 sp = current_stack_frame();
38 else
39 sp = task->thread.ksp;
40
41 for (;;) {
42 unsigned long *stack = (unsigned long *) sp;
43 unsigned long newsp, ip;
44
45 if (!validate_sp(sp, task, STACK_FRAME_OVERHEAD))
46 return;
47
48 newsp = stack[0];
49 ip = stack[STACK_FRAME_LR_SAVE];
50
51 if (!consume_entry(cookie, ip))
52 return;
53
54 sp = newsp;
55 }
56 }
57
58 /*
59 * This function returns an error if it detects any unreliable features of the
60 * stack. Otherwise it guarantees that the stack trace is reliable.
61 *
62 * If the task is not 'current', the caller *must* ensure the task is inactive.
63 */
arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,void * cookie,struct task_struct * task)64 int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
65 void *cookie, struct task_struct *task)
66 {
67 unsigned long sp;
68 unsigned long newsp;
69 unsigned long stack_page = (unsigned long)task_stack_page(task);
70 unsigned long stack_end;
71 int graph_idx = 0;
72 bool firstframe;
73
74 stack_end = stack_page + THREAD_SIZE;
75 if (!is_idle_task(task)) {
76 /*
77 * For user tasks, this is the SP value loaded on
78 * kernel entry, see "PACAKSAVE(r13)" in _switch() and
79 * system_call_common()/EXCEPTION_PROLOG_COMMON().
80 *
81 * Likewise for non-swapper kernel threads,
82 * this also happens to be the top of the stack
83 * as setup by copy_thread().
84 *
85 * Note that stack backlinks are not properly setup by
86 * copy_thread() and thus, a forked task() will have
87 * an unreliable stack trace until it's been
88 * _switch()'ed to for the first time.
89 */
90 stack_end -= STACK_FRAME_OVERHEAD + sizeof(struct pt_regs);
91 } else {
92 /*
93 * idle tasks have a custom stack layout,
94 * c.f. cpu_idle_thread_init().
95 */
96 stack_end -= STACK_FRAME_OVERHEAD;
97 }
98
99 if (task == current)
100 sp = current_stack_frame();
101 else
102 sp = task->thread.ksp;
103
104 if (sp < stack_page + sizeof(struct thread_struct) ||
105 sp > stack_end - STACK_FRAME_MIN_SIZE) {
106 return -EINVAL;
107 }
108
109 for (firstframe = true; sp != stack_end;
110 firstframe = false, sp = newsp) {
111 unsigned long *stack = (unsigned long *) sp;
112 unsigned long ip;
113
114 /* sanity check: ABI requires SP to be aligned 16 bytes. */
115 if (sp & 0xF)
116 return -EINVAL;
117
118 newsp = stack[0];
119 /* Stack grows downwards; unwinder may only go up. */
120 if (newsp <= sp)
121 return -EINVAL;
122
123 if (newsp != stack_end &&
124 newsp > stack_end - STACK_FRAME_MIN_SIZE) {
125 return -EINVAL; /* invalid backlink, too far up. */
126 }
127
128 /*
129 * We can only trust the bottom frame's backlink, the
130 * rest of the frame may be uninitialized, continue to
131 * the next.
132 */
133 if (firstframe)
134 continue;
135
136 /* Mark stacktraces with exception frames as unreliable. */
137 if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
138 stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
139 return -EINVAL;
140 }
141
142 /* Examine the saved LR: it must point into kernel code. */
143 ip = stack[STACK_FRAME_LR_SAVE];
144 if (!__kernel_text_address(ip))
145 return -EINVAL;
146
147 /*
148 * FIXME: IMHO these tests do not belong in
149 * arch-dependent code, they are generic.
150 */
151 ip = ftrace_graph_ret_addr(task, &graph_idx, ip, stack);
152 #ifdef CONFIG_KPROBES
153 /*
154 * Mark stacktraces with kretprobed functions on them
155 * as unreliable.
156 */
157 if (ip == (unsigned long)kretprobe_trampoline)
158 return -EINVAL;
159 #endif
160
161 if (!consume_entry(cookie, ip))
162 return -EINVAL;
163 }
164 return 0;
165 }
166
167 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI)
handle_backtrace_ipi(struct pt_regs * regs)168 static void handle_backtrace_ipi(struct pt_regs *regs)
169 {
170 nmi_cpu_backtrace(regs);
171 }
172
raise_backtrace_ipi(cpumask_t * mask)173 static void raise_backtrace_ipi(cpumask_t *mask)
174 {
175 unsigned int cpu;
176
177 for_each_cpu(cpu, mask) {
178 if (cpu == smp_processor_id())
179 handle_backtrace_ipi(NULL);
180 else
181 smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, 5 * USEC_PER_SEC);
182 }
183
184 for_each_cpu(cpu, mask) {
185 struct paca_struct *p = paca_ptrs[cpu];
186
187 cpumask_clear_cpu(cpu, mask);
188
189 pr_warn("CPU %d didn't respond to backtrace IPI, inspecting paca.\n", cpu);
190 if (!virt_addr_valid(p)) {
191 pr_warn("paca pointer appears corrupt? (%px)\n", p);
192 continue;
193 }
194
195 pr_warn("irq_soft_mask: 0x%02x in_mce: %d in_nmi: %d",
196 p->irq_soft_mask, p->in_mce, p->in_nmi);
197
198 if (virt_addr_valid(p->__current))
199 pr_cont(" current: %d (%s)\n", p->__current->pid,
200 p->__current->comm);
201 else
202 pr_cont(" current pointer corrupt? (%px)\n", p->__current);
203
204 pr_warn("Back trace of paca->saved_r1 (0x%016llx) (possibly stale):\n", p->saved_r1);
205 show_stack(p->__current, (unsigned long *)p->saved_r1, KERN_WARNING);
206 }
207 }
208
arch_trigger_cpumask_backtrace(const cpumask_t * mask,bool exclude_self)209 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
210 {
211 nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
212 }
213 #endif /* defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI) */
214