1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Performance events callchain code, extracted from core.c:
4 *
5 * Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
6 * Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
7 * Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
8 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
9 */
10
11 #include <linux/perf_event.h>
12 #include <linux/slab.h>
13 #include <linux/sched/task_stack.h>
14 #include <linux/uprobes.h>
15
16 #include "internal.h"
17
18 struct callchain_cpus_entries {
19 struct rcu_head rcu_head;
20 struct perf_callchain_entry *cpu_entries[];
21 };
22
23 int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
24 int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
25
26 static inline size_t perf_callchain_entry__sizeof(void)
27 {
28 return (sizeof(struct perf_callchain_entry) +
29 sizeof(__u64) * (sysctl_perf_event_max_stack +
30 sysctl_perf_event_max_contexts_per_stack));
31 }
32
33 static DEFINE_PER_CPU(u8, callchain_recursion[PERF_NR_CONTEXTS]);
34 static atomic_t nr_callchain_events;
35 static DEFINE_MUTEX(callchain_mutex);
36 static struct callchain_cpus_entries *callchain_cpus_entries;
37
38
39 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
40 struct pt_regs *regs)
41 {
42 }
43
44 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
45 struct pt_regs *regs)
46 {
47 }
48
49 static void release_callchain_buffers_rcu(struct rcu_head *head)
50 {
51 struct callchain_cpus_entries *entries;
52 int cpu;
53
54 entries = container_of(head, struct callchain_cpus_entries, rcu_head);
55
56 for_each_possible_cpu(cpu)
57 kfree(entries->cpu_entries[cpu]);
58
59 kfree(entries);
60 }
61
62 static void release_callchain_buffers(void)
63 {
64 struct callchain_cpus_entries *entries;
65
66 entries = callchain_cpus_entries;
67 RCU_INIT_POINTER(callchain_cpus_entries, NULL);
68 call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
69 }
70
71 static int alloc_callchain_buffers(void)
72 {
73 int cpu;
74 int size;
75 struct callchain_cpus_entries *entries;
76
77 /*
78 * We can't use the percpu allocation API for data that can be
79 * accessed from NMI. Use a temporary manual per cpu allocation
80 * until that gets sorted out.
81 */
82 size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
83
84 entries = kzalloc(size, GFP_KERNEL);
85 if (!entries)
86 return -ENOMEM;
87
88 size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
89
90 for_each_possible_cpu(cpu) {
91 entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
92 cpu_to_node(cpu));
93 if (!entries->cpu_entries[cpu])
94 goto fail;
95 }
96
97 rcu_assign_pointer(callchain_cpus_entries, entries);
98
99 return 0;
100
101 fail:
102 for_each_possible_cpu(cpu)
103 kfree(entries->cpu_entries[cpu]);
104 kfree(entries);
105
106 return -ENOMEM;
107 }
108
109 int get_callchain_buffers(int event_max_stack)
110 {
111 int err = 0;
112 int count;
113
114 mutex_lock(&callchain_mutex);
115
116 count = atomic_inc_return(&nr_callchain_events);
117 if (WARN_ON_ONCE(count < 1)) {
118 err = -EINVAL;
119 goto exit;
120 }
121
122 /*
123 * If requesting per event more than the global cap,
124 * return a different error to help userspace figure
125 * this out.
126 *
127 * And also do it here so that we have &callchain_mutex held.
128 */
129 if (event_max_stack > sysctl_perf_event_max_stack) {
130 err = -EOVERFLOW;
131 goto exit;
132 }
133
134 if (count == 1)
135 err = alloc_callchain_buffers();
136 exit:
137 if (err)
138 atomic_dec(&nr_callchain_events);
139
140 mutex_unlock(&callchain_mutex);
141
142 return err;
143 }
144
145 void put_callchain_buffers(void)
146 {
147 if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
148 release_callchain_buffers();
149 mutex_unlock(&callchain_mutex);
150 }
151 }
152
153 struct perf_callchain_entry *get_callchain_entry(int *rctx)
154 {
155 int cpu;
156 struct callchain_cpus_entries *entries;
157
158 *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
159 if (*rctx == -1)
160 return NULL;
161
162 entries = rcu_dereference(callchain_cpus_entries);
163 if (!entries) {
164 put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
165 return NULL;
166 }
167
168 cpu = smp_processor_id();
169
170 return (((void *)entries->cpu_entries[cpu]) +
171 (*rctx * perf_callchain_entry__sizeof()));
172 }
173
174 void
175 put_callchain_entry(int rctx)
176 {
177 put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
178 }
179
180 static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entry,
181 int start_entry_idx)
182 {
183 #ifdef CONFIG_UPROBES
184 struct uprobe_task *utask = current->utask;
185 struct return_instance *ri;
186 __u64 *cur_ip, *last_ip, tramp_addr;
187
188 if (likely(!utask || !utask->return_instances))
189 return;
190
191 cur_ip = &entry->ip[start_entry_idx];
192 last_ip = &entry->ip[entry->nr - 1];
193 ri = utask->return_instances;
194 tramp_addr = uprobe_get_trampoline_vaddr();
195
196 /*
197 * If there are pending uretprobes for the current thread, they are
198 * recorded in a list inside utask->return_instances; each such
199 * pending uretprobe replaces traced user function's return address on
200 * the stack, so when stack trace is captured, instead of seeing
201 * actual function's return address, we'll have one or many uretprobe
202 * trampoline addresses in the stack trace, which are not helpful and
203 * misleading to users.
204 * So here we go over the pending list of uretprobes, and each
205 * encountered trampoline address is replaced with actual return
206 * address.
207 */
208 while (ri && cur_ip <= last_ip) {
209 if (*cur_ip == tramp_addr) {
210 *cur_ip = ri->orig_ret_vaddr;
211 ri = ri->next;
212 }
213 cur_ip++;
214 }
215 #endif
216 }
217
218 struct perf_callchain_entry *
219 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
220 u32 max_stack, bool crosstask, bool add_mark)
221 {
222 struct perf_callchain_entry *entry;
223 struct perf_callchain_entry_ctx ctx;
224 int rctx, start_entry_idx;
225
226 entry = get_callchain_entry(&rctx);
227 if (!entry)
228 return NULL;
229
230 ctx.entry = entry;
231 ctx.max_stack = max_stack;
232 ctx.nr = entry->nr = init_nr;
233 ctx.contexts = 0;
234 ctx.contexts_maxed = false;
235
236 if (kernel && !user_mode(regs)) {
237 if (add_mark)
238 perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
239 perf_callchain_kernel(&ctx, regs);
240 }
241
242 if (user) {
243 if (!user_mode(regs)) {
244 if (current->mm)
245 regs = task_pt_regs(current);
246 else
247 regs = NULL;
248 }
249
250 if (regs) {
251 if (crosstask)
252 goto exit_put;
253
254 if (add_mark)
255 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
256
257 start_entry_idx = entry->nr;
258 perf_callchain_user(&ctx, regs);
259 fixup_uretprobe_trampoline_entries(entry, start_entry_idx);
260 }
261 }
262
263 exit_put:
264 put_callchain_entry(rctx);
265
266 return entry;
267 }
268
269 /*
270 * Used for sysctl_perf_event_max_stack and
271 * sysctl_perf_event_max_contexts_per_stack.
272 */
273 int perf_event_max_stack_handler(const struct ctl_table *table, int write,
274 void *buffer, size_t *lenp, loff_t *ppos)
275 {
276 int *value = table->data;
277 int new_value = *value, ret;
278 struct ctl_table new_table = *table;
279
280 new_table.data = &new_value;
281 ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
282 if (ret || !write)
283 return ret;
284
285 mutex_lock(&callchain_mutex);
286 if (atomic_read(&nr_callchain_events))
287 ret = -EBUSY;
288 else
289 *value = new_value;
290
291 mutex_unlock(&callchain_mutex);
292
293 return ret;
294 }
295
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