1 // SPDX-License-Identifier: GPL-2.0+ 1
2 /*
3 * Restartable sequences system call
4 *
5 * Copyright (C) 2015, Google, Inc.,
6 * Paul Turner <pjt@google.com> and Andrew Hun
7 * Copyright (C) 2015-2018, EfficiOS Inc.,
8 * Mathieu Desnoyers <mathieu.desnoyers@effici
9 */
10
11 #include <linux/sched.h>
12 #include <linux/uaccess.h>
13 #include <linux/syscalls.h>
14 #include <linux/rseq.h>
15 #include <linux/types.h>
16 #include <asm/ptrace.h>
17
18 #define CREATE_TRACE_POINTS
19 #include <trace/events/rseq.h>
20
21 /* The original rseq structure size (including
22 #define ORIG_RSEQ_SIZE 32
23
24 #define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG
25 RSEQ_CS_FLAG
26 RSEQ_CS_FLAG
27
28 /*
29 *
30 * Restartable sequences are a lightweight int
31 * user-level code to be executed atomically r
32 * preemption and signal delivery. Typically u
33 * per-cpu operations.
34 *
35 * It allows user-space to perform update oper
36 * without requiring heavy-weight atomic opera
37 *
38 * Detailed algorithm of rseq user-space assem
39 *
40 * init(rseq_cs)
41 * cpu = TLS->rseq::cpu_id
42 * [1] TLS->rseq::rseq_cs = rs
43 * [start_ip] -----------------------
44 * [2] if (cpu != TLS->rseq::c
45 * goto abort_ip;
46 * [3] <last_instruction_in_cs
47 * [post_commit_ip] -----------------------
48 *
49 * The address of jump target abort_ip must
50 * region, i.e.:
51 *
52 * [abort_ip] < [start_ip] || [abort_ip]
53 *
54 * Steps [2]-[3] (inclusive) need to be a se
55 * userspace that can handle being interrupt
56 * instructions, and then resumed to the abo
57 *
58 * 1. Userspace stores the address of the s
59 * block descriptor into the rseq_cs fie
60 * struct rseq TLS area. This update is
61 * store within the inline assembly inst
62 * [start_ip]
63 *
64 * 2. Userspace tests to check whether the
65 * the cpu number loaded before start_ip
66 * in case of a mismatch.
67 *
68 * If the sequence is preempted or inter
69 * at or after start_ip and before post_
70 * clears TLS->__rseq_abi::rseq_cs, and
71 * ip to abort_ip before returning to us
72 * execution resumes at abort_ip.
73 *
74 * 3. Userspace critical section final inst
75 * post_commit_ip is the commit. The cri
76 * self-terminating.
77 * [post_commit_ip]
78 *
79 * 4. <success>
80 *
81 * On failure at [2], or if interrupted by p
82 * between [1] and [3]:
83 *
84 * [abort_ip]
85 * F1. <failure>
86 */
87
88 static int rseq_update_cpu_node_id(struct task
89 {
90 struct rseq __user *rseq = t->rseq;
91 u32 cpu_id = raw_smp_processor_id();
92 u32 node_id = cpu_to_node(cpu_id);
93 u32 mm_cid = task_mm_cid(t);
94
95 WARN_ON_ONCE((int) mm_cid < 0);
96 if (!user_write_access_begin(rseq, t->
97 goto efault;
98 unsafe_put_user(cpu_id, &rseq->cpu_id_
99 unsafe_put_user(cpu_id, &rseq->cpu_id,
100 unsafe_put_user(node_id, &rseq->node_i
101 unsafe_put_user(mm_cid, &rseq->mm_cid,
102 /*
103 * Additional feature fields added aft
104 * need to be conditionally updated on
105 * t->rseq_len != ORIG_RSEQ_SIZE.
106 */
107 user_write_access_end();
108 trace_rseq_update(t);
109 return 0;
110
111 efault_end:
112 user_write_access_end();
113 efault:
114 return -EFAULT;
115 }
116
117 static int rseq_reset_rseq_cpu_node_id(struct
118 {
119 u32 cpu_id_start = 0, cpu_id = RSEQ_CP
120 mm_cid = 0;
121
122 /*
123 * Reset cpu_id_start to its initial s
124 */
125 if (put_user(cpu_id_start, &t->rseq->c
126 return -EFAULT;
127 /*
128 * Reset cpu_id to RSEQ_CPU_ID_UNINITI
129 * in after unregistration can figure
130 * registered again.
131 */
132 if (put_user(cpu_id, &t->rseq->cpu_id)
133 return -EFAULT;
134 /*
135 * Reset node_id to its initial state
136 */
137 if (put_user(node_id, &t->rseq->node_i
138 return -EFAULT;
139 /*
140 * Reset mm_cid to its initial state (
141 */
142 if (put_user(mm_cid, &t->rseq->mm_cid)
143 return -EFAULT;
144 /*
145 * Additional feature fields added aft
146 * need to be conditionally reset only
147 * t->rseq_len != ORIG_RSEQ_SIZE.
148 */
149 return 0;
150 }
151
152 static int rseq_get_rseq_cs(struct task_struct
153 {
154 struct rseq_cs __user *urseq_cs;
155 u64 ptr;
156 u32 __user *usig;
157 u32 sig;
158 int ret;
159
160 #ifdef CONFIG_64BIT
161 if (get_user(ptr, &t->rseq->rseq_cs))
162 return -EFAULT;
163 #else
164 if (copy_from_user(&ptr, &t->rseq->rse
165 return -EFAULT;
166 #endif
167 if (!ptr) {
168 memset(rseq_cs, 0, sizeof(*rse
169 return 0;
170 }
171 if (ptr >= TASK_SIZE)
172 return -EINVAL;
173 urseq_cs = (struct rseq_cs __user *)(u
174 if (copy_from_user(rseq_cs, urseq_cs,
175 return -EFAULT;
176
177 if (rseq_cs->start_ip >= TASK_SIZE ||
178 rseq_cs->start_ip + rseq_cs->post_
179 rseq_cs->abort_ip >= TASK_SIZE ||
180 rseq_cs->version > 0)
181 return -EINVAL;
182 /* Check for overflow. */
183 if (rseq_cs->start_ip + rseq_cs->post_
184 return -EINVAL;
185 /* Ensure that abort_ip is not in the
186 if (rseq_cs->abort_ip - rseq_cs->start
187 return -EINVAL;
188
189 usig = (u32 __user *)(unsigned long)(r
190 ret = get_user(sig, usig);
191 if (ret)
192 return ret;
193
194 if (current->rseq_sig != sig) {
195 printk_ratelimited(KERN_WARNIN
196 "Possible attack attem
197 sig, current->rseq_sig
198 return -EINVAL;
199 }
200 return 0;
201 }
202
203 static bool rseq_warn_flags(const char *str, u
204 {
205 u32 test_flags;
206
207 if (!flags)
208 return false;
209 test_flags = flags & RSEQ_CS_NO_RESTAR
210 if (test_flags)
211 pr_warn_once("Deprecated flags
212 test_flags = flags & ~RSEQ_CS_NO_RESTA
213 if (test_flags)
214 pr_warn_once("Unknown flags (%
215 return true;
216 }
217
218 static int rseq_need_restart(struct task_struc
219 {
220 u32 flags, event_mask;
221 int ret;
222
223 if (rseq_warn_flags("rseq_cs", cs_flag
224 return -EINVAL;
225
226 /* Get thread flags. */
227 ret = get_user(flags, &t->rseq->flags)
228 if (ret)
229 return ret;
230
231 if (rseq_warn_flags("rseq", flags))
232 return -EINVAL;
233
234 /*
235 * Load and clear event mask atomicall
236 * scheduler preemption.
237 */
238 preempt_disable();
239 event_mask = t->rseq_event_mask;
240 t->rseq_event_mask = 0;
241 preempt_enable();
242
243 return !!event_mask;
244 }
245
246 static int clear_rseq_cs(struct task_struct *t
247 {
248 /*
249 * The rseq_cs field is set to NULL on
250 * delivery on top of rseq assembly bl
251 * of code outside of the rseq assembl
252 * a lazy clear of the rseq_cs field.
253 *
254 * Set rseq_cs to NULL.
255 */
256 #ifdef CONFIG_64BIT
257 return put_user(0UL, &t->rseq->rseq_cs
258 #else
259 if (clear_user(&t->rseq->rseq_cs, size
260 return -EFAULT;
261 return 0;
262 #endif
263 }
264
265 /*
266 * Unsigned comparison will be true when ip >=
267 * ip < start_ip + post_commit_offset.
268 */
269 static bool in_rseq_cs(unsigned long ip, struc
270 {
271 return ip - rseq_cs->start_ip < rseq_c
272 }
273
274 static int rseq_ip_fixup(struct pt_regs *regs)
275 {
276 unsigned long ip = instruction_pointer
277 struct task_struct *t = current;
278 struct rseq_cs rseq_cs;
279 int ret;
280
281 ret = rseq_get_rseq_cs(t, &rseq_cs);
282 if (ret)
283 return ret;
284
285 /*
286 * Handle potentially not being within
287 * If not nested over a rseq critical
288 * Clear the rseq_cs pointer and retur
289 */
290 if (!in_rseq_cs(ip, &rseq_cs))
291 return clear_rseq_cs(t);
292 ret = rseq_need_restart(t, rseq_cs.fla
293 if (ret <= 0)
294 return ret;
295 ret = clear_rseq_cs(t);
296 if (ret)
297 return ret;
298 trace_rseq_ip_fixup(ip, rseq_cs.start_
299 rseq_cs.abort_ip);
300 instruction_pointer_set(regs, (unsigne
301 return 0;
302 }
303
304 /*
305 * This resume handler must always be executed
306 * - preemption,
307 * - signal delivery,
308 * and return to user-space.
309 *
310 * This is how we can ensure that the entire r
311 * will issue the commit instruction only if e
312 * respect to other threads scheduled on the s
313 * to signal handlers.
314 */
315 void __rseq_handle_notify_resume(struct ksigna
316 {
317 struct task_struct *t = current;
318 int ret, sig;
319
320 if (unlikely(t->flags & PF_EXITING))
321 return;
322
323 /*
324 * regs is NULL if and only if the cal
325 * fixup and leave rseq_cs as is so th
326 * kill a misbehaving userspace on deb
327 */
328 if (regs) {
329 ret = rseq_ip_fixup(regs);
330 if (unlikely(ret < 0))
331 goto error;
332 }
333 if (unlikely(rseq_update_cpu_node_id(t
334 goto error;
335 return;
336
337 error:
338 sig = ksig ? ksig->sig : 0;
339 force_sigsegv(sig);
340 }
341
342 #ifdef CONFIG_DEBUG_RSEQ
343
344 /*
345 * Terminate the process if a syscall is issue
346 * sequence.
347 */
348 void rseq_syscall(struct pt_regs *regs)
349 {
350 unsigned long ip = instruction_pointer
351 struct task_struct *t = current;
352 struct rseq_cs rseq_cs;
353
354 if (!t->rseq)
355 return;
356 if (rseq_get_rseq_cs(t, &rseq_cs) || i
357 force_sig(SIGSEGV);
358 }
359
360 #endif
361
362 /*
363 * sys_rseq - setup restartable sequences for
364 */
365 SYSCALL_DEFINE4(rseq, struct rseq __user *, rs
366 int, flags, u32, sig)
367 {
368 int ret;
369
370 if (flags & RSEQ_FLAG_UNREGISTER) {
371 if (flags & ~RSEQ_FLAG_UNREGIS
372 return -EINVAL;
373 /* Unregister rseq for current
374 if (current->rseq != rseq || !
375 return -EINVAL;
376 if (rseq_len != current->rseq_
377 return -EINVAL;
378 if (current->rseq_sig != sig)
379 return -EPERM;
380 ret = rseq_reset_rseq_cpu_node
381 if (ret)
382 return ret;
383 current->rseq = NULL;
384 current->rseq_sig = 0;
385 current->rseq_len = 0;
386 return 0;
387 }
388
389 if (unlikely(flags))
390 return -EINVAL;
391
392 if (current->rseq) {
393 /*
394 * If rseq is already register
395 * the provided address differ
396 * one.
397 */
398 if (current->rseq != rseq || r
399 return -EINVAL;
400 if (current->rseq_sig != sig)
401 return -EPERM;
402 /* Already registered. */
403 return -EBUSY;
404 }
405
406 /*
407 * If there was no rseq previously reg
408 * is properly aligned, as communcated
409 * auxiliary vector AT_RSEQ_ALIGN. If
410 * size, the required alignment is the
411 *
412 * In order to be valid, rseq_len is e
413 * large enough to contain all support
414 * user-space through the ELF auxiliar
415 */
416 if (rseq_len < ORIG_RSEQ_SIZE ||
417 (rseq_len == ORIG_RSEQ_SIZE && !IS
418 (rseq_len != ORIG_RSEQ_SIZE && (!I
419 rs
420 return -EINVAL;
421 if (!access_ok(rseq, rseq_len))
422 return -EFAULT;
423 current->rseq = rseq;
424 current->rseq_len = rseq_len;
425 current->rseq_sig = sig;
426 /*
427 * If rseq was previously inactive, an
428 * registered, ensure the cpu_id_start
429 * are updated before returning to use
430 */
431 rseq_set_notify_resume(current);
432
433 return 0;
434 }
435
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