1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Restartable sequences system call 4 * 5 * Copyright (C) 2015, Google, Inc., 6 * Paul Turner <pjt@google.com> and Andrew Hunter <ahh@google.com> 7 * Copyright (C) 2015-2018, EfficiOS Inc., 8 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> 9 */ 10 11 /* 12 * Restartable sequences are a lightweight interface that allows 13 * user-level code to be executed atomically relative to scheduler 14 * preemption and signal delivery. Typically used for implementing 15 * per-cpu operations. 16 * 17 * It allows user-space to perform update operations on per-cpu data 18 * without requiring heavy-weight atomic operations. 19 * 20 * Detailed algorithm of rseq user-space assembly sequences: 21 * 22 * init(rseq_cs) 23 * cpu = TLS->rseq::cpu_id_start 24 * [1] TLS->rseq::rseq_cs = rseq_cs 25 * [start_ip] ---------------------------- 26 * [2] if (cpu != TLS->rseq::cpu_id) 27 * goto abort_ip; 28 * [3] <last_instruction_in_cs> 29 * [post_commit_ip] ---------------------------- 30 * 31 * The address of jump target abort_ip must be outside the critical 32 * region, i.e.: 33 * 34 * [abort_ip] < [start_ip] || [abort_ip] >= [post_commit_ip] 35 * 36 * Steps [2]-[3] (inclusive) need to be a sequence of instructions in 37 * userspace that can handle being interrupted between any of those 38 * instructions, and then resumed to the abort_ip. 39 * 40 * 1. Userspace stores the address of the struct rseq_cs assembly 41 * block descriptor into the rseq_cs field of the registered 42 * struct rseq TLS area. This update is performed through a single 43 * store within the inline assembly instruction sequence. 44 * [start_ip] 45 * 46 * 2. Userspace tests to check whether the current cpu_id field match 47 * the cpu number loaded before start_ip, branching to abort_ip 48 * in case of a mismatch. 49 * 50 * If the sequence is preempted or interrupted by a signal 51 * at or after start_ip and before post_commit_ip, then the kernel 52 * clears TLS->__rseq_abi::rseq_cs, and sets the user-space return 53 * ip to abort_ip before returning to user-space, so the preempted 54 * execution resumes at abort_ip. 55 * 56 * 3. Userspace critical section final instruction before 57 * post_commit_ip is the commit. The critical section is 58 * self-terminating. 59 * [post_commit_ip] 60 * 61 * 4. <success> 62 * 63 * On failure at [2], or if interrupted by preempt or signal delivery 64 * between [1] and [3]: 65 * 66 * [abort_ip] 67 * F1. <failure> 68 */ 69 70 /* Required to select the proper per_cpu ops for rseq_stats_inc() */ 71 #define RSEQ_BUILD_SLOW_PATH 72 73 #include <linux/debugfs.h> 74 #include <linux/hrtimer.h> 75 #include <linux/percpu.h> 76 #include <linux/prctl.h> 77 #include <linux/ratelimit.h> 78 #include <linux/rseq_entry.h> 79 #include <linux/sched.h> 80 #include <linux/syscalls.h> 81 #include <linux/uaccess.h> 82 #include <linux/types.h> 83 #include <linux/rseq.h> 84 #include <asm/ptrace.h> 85 86 #define CREATE_TRACE_POINTS 87 #include <trace/events/rseq.h> 88 89 DEFINE_STATIC_KEY_MAYBE(CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE, rseq_debug_enabled); 90 91 static inline void rseq_control_debug(bool on) 92 { 93 if (on) 94 static_branch_enable(&rseq_debug_enabled); 95 else 96 static_branch_disable(&rseq_debug_enabled); 97 } 98 99 static int __init rseq_setup_debug(char *str) 100 { 101 bool on; 102 103 if (kstrtobool(str, &on)) 104 return -EINVAL; 105 rseq_control_debug(on); 106 return 1; 107 } 108 __setup("rseq_debug=", rseq_setup_debug); 109 110 #ifdef CONFIG_TRACEPOINTS 111 /* 112 * Out of line, so the actual update functions can be in a header to be 113 * inlined into the exit to user code. 114 */ 115 void __rseq_trace_update(struct task_struct *t) 116 { 117 trace_rseq_update(t); 118 } 119 120 void __rseq_trace_ip_fixup(unsigned long ip, unsigned long start_ip, 121 unsigned long offset, unsigned long abort_ip) 122 { 123 trace_rseq_ip_fixup(ip, start_ip, offset, abort_ip); 124 } 125 #endif /* CONFIG_TRACEPOINTS */ 126 127 #ifdef CONFIG_RSEQ_STATS 128 DEFINE_PER_CPU(struct rseq_stats, rseq_stats); 129 130 static int rseq_stats_show(struct seq_file *m, void *p) 131 { 132 struct rseq_stats stats = { }; 133 unsigned int cpu; 134 135 for_each_possible_cpu(cpu) { 136 stats.exit += data_race(per_cpu(rseq_stats.exit, cpu)); 137 stats.signal += data_race(per_cpu(rseq_stats.signal, cpu)); 138 stats.slowpath += data_race(per_cpu(rseq_stats.slowpath, cpu)); 139 stats.fastpath += data_race(per_cpu(rseq_stats.fastpath, cpu)); 140 stats.ids += data_race(per_cpu(rseq_stats.ids, cpu)); 141 stats.cs += data_race(per_cpu(rseq_stats.cs, cpu)); 142 stats.clear += data_race(per_cpu(rseq_stats.clear, cpu)); 143 stats.fixup += data_race(per_cpu(rseq_stats.fixup, cpu)); 144 if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) { 145 stats.s_granted += data_race(per_cpu(rseq_stats.s_granted, cpu)); 146 stats.s_expired += data_race(per_cpu(rseq_stats.s_expired, cpu)); 147 stats.s_revoked += data_race(per_cpu(rseq_stats.s_revoked, cpu)); 148 stats.s_yielded += data_race(per_cpu(rseq_stats.s_yielded, cpu)); 149 stats.s_aborted += data_race(per_cpu(rseq_stats.s_aborted, cpu)); 150 } 151 } 152 153 seq_printf(m, "exit: %16lu\n", stats.exit); 154 seq_printf(m, "signal: %16lu\n", stats.signal); 155 seq_printf(m, "slowp: %16lu\n", stats.slowpath); 156 seq_printf(m, "fastp: %16lu\n", stats.fastpath); 157 seq_printf(m, "ids: %16lu\n", stats.ids); 158 seq_printf(m, "cs: %16lu\n", stats.cs); 159 seq_printf(m, "clear: %16lu\n", stats.clear); 160 seq_printf(m, "fixup: %16lu\n", stats.fixup); 161 if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) { 162 seq_printf(m, "sgrant: %16lu\n", stats.s_granted); 163 seq_printf(m, "sexpir: %16lu\n", stats.s_expired); 164 seq_printf(m, "srevok: %16lu\n", stats.s_revoked); 165 seq_printf(m, "syield: %16lu\n", stats.s_yielded); 166 seq_printf(m, "sabort: %16lu\n", stats.s_aborted); 167 } 168 return 0; 169 } 170 171 static int rseq_stats_open(struct inode *inode, struct file *file) 172 { 173 return single_open(file, rseq_stats_show, inode->i_private); 174 } 175 176 static const struct file_operations stat_ops = { 177 .open = rseq_stats_open, 178 .read = seq_read, 179 .llseek = seq_lseek, 180 .release = single_release, 181 }; 182 183 static int __init rseq_stats_init(struct dentry *root_dir) 184 { 185 debugfs_create_file("stats", 0444, root_dir, NULL, &stat_ops); 186 return 0; 187 } 188 #else 189 static inline void rseq_stats_init(struct dentry *root_dir) { } 190 #endif /* CONFIG_RSEQ_STATS */ 191 192 static int rseq_debug_show(struct seq_file *m, void *p) 193 { 194 bool on = static_branch_unlikely(&rseq_debug_enabled); 195 196 seq_printf(m, "%d\n", on); 197 return 0; 198 } 199 200 static ssize_t rseq_debug_write(struct file *file, const char __user *ubuf, 201 size_t count, loff_t *ppos) 202 { 203 bool on; 204 205 if (kstrtobool_from_user(ubuf, count, &on)) 206 return -EINVAL; 207 208 rseq_control_debug(on); 209 return count; 210 } 211 212 static int rseq_debug_open(struct inode *inode, struct file *file) 213 { 214 return single_open(file, rseq_debug_show, inode->i_private); 215 } 216 217 static const struct file_operations debug_ops = { 218 .open = rseq_debug_open, 219 .read = seq_read, 220 .write = rseq_debug_write, 221 .llseek = seq_lseek, 222 .release = single_release, 223 }; 224 225 static void rseq_slice_ext_init(struct dentry *root_dir); 226 227 static int __init rseq_debugfs_init(void) 228 { 229 struct dentry *root_dir = debugfs_create_dir("rseq", NULL); 230 231 debugfs_create_file("debug", 0644, root_dir, NULL, &debug_ops); 232 rseq_stats_init(root_dir); 233 if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) 234 rseq_slice_ext_init(root_dir); 235 return 0; 236 } 237 __initcall(rseq_debugfs_init); 238 239 static bool rseq_set_ids(struct task_struct *t, struct rseq_ids *ids, u32 node_id) 240 { 241 return rseq_set_ids_get_csaddr(t, ids, node_id, NULL); 242 } 243 244 static bool rseq_handle_cs(struct task_struct *t, struct pt_regs *regs) 245 { 246 struct rseq __user *urseq = t->rseq.usrptr; 247 u64 csaddr; 248 249 scoped_user_read_access(urseq, efault) 250 unsafe_get_user(csaddr, &urseq->rseq_cs, efault); 251 if (likely(!csaddr)) 252 return true; 253 return rseq_update_user_cs(t, regs, csaddr); 254 efault: 255 return false; 256 } 257 258 static void rseq_slowpath_update_usr(struct pt_regs *regs) 259 { 260 /* 261 * Preserve rseq state and user_irq state. The generic entry code 262 * clears user_irq on the way out, the non-generic entry 263 * architectures are not having user_irq. 264 */ 265 const struct rseq_event evt_mask = { .has_rseq = true, .user_irq = true, }; 266 struct task_struct *t = current; 267 struct rseq_ids ids; 268 u32 node_id; 269 bool event; 270 271 if (unlikely(t->flags & PF_EXITING)) 272 return; 273 274 rseq_stat_inc(rseq_stats.slowpath); 275 276 /* 277 * Read and clear the event pending bit first. If the task 278 * was not preempted or migrated or a signal is on the way, 279 * there is no point in doing any of the heavy lifting here 280 * on production kernels. In that case TIF_NOTIFY_RESUME 281 * was raised by some other functionality. 282 * 283 * This is correct because the read/clear operation is 284 * guarded against scheduler preemption, which makes it CPU 285 * local atomic. If the task is preempted right after 286 * re-enabling preemption then TIF_NOTIFY_RESUME is set 287 * again and this function is invoked another time _before_ 288 * the task is able to return to user mode. 289 * 290 * On a debug kernel, invoke the fixup code unconditionally 291 * with the result handed in to allow the detection of 292 * inconsistencies. 293 */ 294 scoped_guard(irq) { 295 event = t->rseq.event.sched_switch; 296 t->rseq.event.all &= evt_mask.all; 297 ids.cpu_id = task_cpu(t); 298 ids.mm_cid = task_mm_cid(t); 299 } 300 301 if (!event) 302 return; 303 304 node_id = cpu_to_node(ids.cpu_id); 305 306 if (unlikely(!rseq_update_usr(t, regs, &ids, node_id))) { 307 /* 308 * Clear the errors just in case this might survive magically, but 309 * leave the rest intact. 310 */ 311 t->rseq.event.error = 0; 312 force_sig(SIGSEGV); 313 } 314 } 315 316 void __rseq_handle_slowpath(struct pt_regs *regs) 317 { 318 /* 319 * If invoked from hypervisors before entering the guest via 320 * resume_user_mode_work(), then @regs is a NULL pointer. 321 * 322 * resume_user_mode_work() clears TIF_NOTIFY_RESUME and re-raises 323 * it before returning from the ioctl() to user space when 324 * rseq_event.sched_switch is set. 325 * 326 * So it's safe to ignore here instead of pointlessly updating it 327 * in the vcpu_run() loop. 328 */ 329 if (!regs) 330 return; 331 332 rseq_slowpath_update_usr(regs); 333 } 334 335 void __rseq_signal_deliver(int sig, struct pt_regs *regs) 336 { 337 rseq_stat_inc(rseq_stats.signal); 338 /* 339 * Don't update IDs, they are handled on exit to user if 340 * necessary. The important thing is to abort a critical section of 341 * the interrupted context as after this point the instruction 342 * pointer in @regs points to the signal handler. 343 */ 344 if (unlikely(!rseq_handle_cs(current, regs))) { 345 /* 346 * Clear the errors just in case this might survive 347 * magically, but leave the rest intact. 348 */ 349 current->rseq.event.error = 0; 350 force_sigsegv(sig); 351 } 352 } 353 354 /* 355 * Terminate the process if a syscall is issued within a restartable 356 * sequence. 357 */ 358 void __rseq_debug_syscall_return(struct pt_regs *regs) 359 { 360 struct task_struct *t = current; 361 u64 csaddr; 362 363 if (!t->rseq.event.has_rseq) 364 return; 365 if (get_user(csaddr, &t->rseq.usrptr->rseq_cs)) 366 goto fail; 367 if (likely(!csaddr)) 368 return; 369 if (unlikely(csaddr >= TASK_SIZE)) 370 goto fail; 371 if (rseq_debug_update_user_cs(t, regs, csaddr)) 372 return; 373 fail: 374 force_sig(SIGSEGV); 375 } 376 377 #ifdef CONFIG_DEBUG_RSEQ 378 /* Kept around to keep GENERIC_ENTRY=n architectures supported. */ 379 void rseq_syscall(struct pt_regs *regs) 380 { 381 __rseq_debug_syscall_return(regs); 382 } 383 #endif 384 385 static bool rseq_reset_ids(void) 386 { 387 struct rseq_ids ids = { 388 .cpu_id = RSEQ_CPU_ID_UNINITIALIZED, 389 .mm_cid = 0, 390 }; 391 392 /* 393 * If this fails, terminate it because this leaves the kernel in 394 * stupid state as exit to user space will try to fixup the ids 395 * again. 396 */ 397 if (rseq_set_ids(current, &ids, 0)) 398 return true; 399 400 force_sig(SIGSEGV); 401 return false; 402 } 403 404 /* The original rseq structure size (including padding) is 32 bytes. */ 405 #define ORIG_RSEQ_SIZE 32 406 407 /* 408 * sys_rseq - setup restartable sequences for caller thread. 409 */ 410 SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32, sig) 411 { 412 u32 rseqfl = 0; 413 414 if (flags & RSEQ_FLAG_UNREGISTER) { 415 if (flags & ~RSEQ_FLAG_UNREGISTER) 416 return -EINVAL; 417 /* Unregister rseq for current thread. */ 418 if (current->rseq.usrptr != rseq || !current->rseq.usrptr) 419 return -EINVAL; 420 if (rseq_len != current->rseq.len) 421 return -EINVAL; 422 if (current->rseq.sig != sig) 423 return -EPERM; 424 if (!rseq_reset_ids()) 425 return -EFAULT; 426 rseq_reset(current); 427 return 0; 428 } 429 430 if (unlikely(flags & ~(RSEQ_FLAG_SLICE_EXT_DEFAULT_ON))) 431 return -EINVAL; 432 433 if (current->rseq.usrptr) { 434 /* 435 * If rseq is already registered, check whether 436 * the provided address differs from the prior 437 * one. 438 */ 439 if (current->rseq.usrptr != rseq || rseq_len != current->rseq.len) 440 return -EINVAL; 441 if (current->rseq.sig != sig) 442 return -EPERM; 443 /* Already registered. */ 444 return -EBUSY; 445 } 446 447 /* 448 * If there was no rseq previously registered, ensure the provided rseq 449 * is properly aligned, as communcated to user-space through the ELF 450 * auxiliary vector AT_RSEQ_ALIGN. If rseq_len is the original rseq 451 * size, the required alignment is the original struct rseq alignment. 452 * 453 * The rseq_len is required to be greater or equal to the original rseq 454 * size. In order to be valid, rseq_len is either the original rseq size, 455 * or large enough to contain all supported fields, as communicated to 456 * user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE. 457 */ 458 if (rseq_len < ORIG_RSEQ_SIZE || 459 (rseq_len == ORIG_RSEQ_SIZE && !IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE)) || 460 (rseq_len != ORIG_RSEQ_SIZE && (!IS_ALIGNED((unsigned long)rseq, rseq_alloc_align()) || 461 rseq_len < offsetof(struct rseq, end)))) 462 return -EINVAL; 463 if (!access_ok(rseq, rseq_len)) 464 return -EFAULT; 465 466 if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) { 467 rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE; 468 if (rseq_slice_extension_enabled() && 469 (flags & RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)) 470 rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED; 471 } 472 473 scoped_user_write_access(rseq, efault) { 474 /* 475 * If the rseq_cs pointer is non-NULL on registration, clear it to 476 * avoid a potential segfault on return to user-space. The proper thing 477 * to do would have been to fail the registration but this would break 478 * older libcs that reuse the rseq area for new threads without 479 * clearing the fields. Don't bother reading it, just reset it. 480 */ 481 unsafe_put_user(0UL, &rseq->rseq_cs, efault); 482 unsafe_put_user(rseqfl, &rseq->flags, efault); 483 /* Initialize IDs in user space */ 484 unsafe_put_user(RSEQ_CPU_ID_UNINITIALIZED, &rseq->cpu_id_start, efault); 485 unsafe_put_user(RSEQ_CPU_ID_UNINITIALIZED, &rseq->cpu_id, efault); 486 unsafe_put_user(0U, &rseq->node_id, efault); 487 unsafe_put_user(0U, &rseq->mm_cid, efault); 488 unsafe_put_user(0U, &rseq->slice_ctrl.all, efault); 489 } 490 491 /* 492 * Activate the registration by setting the rseq area address, length 493 * and signature in the task struct. 494 */ 495 current->rseq.usrptr = rseq; 496 current->rseq.len = rseq_len; 497 current->rseq.sig = sig; 498 499 #ifdef CONFIG_RSEQ_SLICE_EXTENSION 500 current->rseq.slice.state.enabled = !!(rseqfl & RSEQ_CS_FLAG_SLICE_EXT_ENABLED); 501 #endif 502 503 /* 504 * If rseq was previously inactive, and has just been 505 * registered, ensure the cpu_id_start and cpu_id fields 506 * are updated before returning to user-space. 507 */ 508 current->rseq.event.has_rseq = true; 509 rseq_force_update(); 510 return 0; 511 512 efault: 513 return -EFAULT; 514 } 515 516 #ifdef CONFIG_RSEQ_SLICE_EXTENSION 517 struct slice_timer { 518 struct hrtimer timer; 519 void *cookie; 520 }; 521 522 static const unsigned int rseq_slice_ext_nsecs_min = 5 * NSEC_PER_USEC; 523 static const unsigned int rseq_slice_ext_nsecs_max = 50 * NSEC_PER_USEC; 524 unsigned int rseq_slice_ext_nsecs __read_mostly = rseq_slice_ext_nsecs_min; 525 static DEFINE_PER_CPU(struct slice_timer, slice_timer); 526 DEFINE_STATIC_KEY_TRUE(rseq_slice_extension_key); 527 528 /* 529 * When the timer expires and the task is still in user space, the return 530 * from interrupt will revoke the grant and schedule. If the task already 531 * entered the kernel via a syscall and the timer fires before the syscall 532 * work was able to cancel it, then depending on the preemption model this 533 * will either reschedule on return from interrupt or in the syscall work 534 * below. 535 */ 536 static enum hrtimer_restart rseq_slice_expired(struct hrtimer *tmr) 537 { 538 struct slice_timer *st = container_of(tmr, struct slice_timer, timer); 539 540 /* 541 * Validate that the task which armed the timer is still on the 542 * CPU. It could have been scheduled out without canceling the 543 * timer. 544 */ 545 if (st->cookie == current && current->rseq.slice.state.granted) { 546 rseq_stat_inc(rseq_stats.s_expired); 547 set_need_resched_current(); 548 } 549 return HRTIMER_NORESTART; 550 } 551 552 bool __rseq_arm_slice_extension_timer(void) 553 { 554 struct slice_timer *st = this_cpu_ptr(&slice_timer); 555 struct task_struct *curr = current; 556 557 lockdep_assert_irqs_disabled(); 558 559 /* 560 * This check prevents a task, which got a time slice extension 561 * granted, from exceeding the maximum scheduling latency when the 562 * grant expired before going out to user space. Don't bother to 563 * clear the grant here, it will be cleaned up automatically before 564 * going out to user space after being scheduled back in. 565 */ 566 if ((unlikely(curr->rseq.slice.expires < ktime_get_mono_fast_ns()))) { 567 set_need_resched_current(); 568 return true; 569 } 570 571 /* 572 * Store the task pointer as a cookie for comparison in the timer 573 * function. This is safe as the timer is CPU local and cannot be 574 * in the expiry function at this point. 575 */ 576 st->cookie = curr; 577 hrtimer_start(&st->timer, curr->rseq.slice.expires, HRTIMER_MODE_ABS_PINNED_HARD); 578 /* Arm the syscall entry work */ 579 set_task_syscall_work(curr, SYSCALL_RSEQ_SLICE); 580 return false; 581 } 582 583 static void rseq_cancel_slice_extension_timer(void) 584 { 585 struct slice_timer *st = this_cpu_ptr(&slice_timer); 586 587 /* 588 * st->cookie can be safely read as preemption is disabled and the 589 * timer is CPU local. 590 * 591 * As this is most probably the first expiring timer, the cancel is 592 * expensive as it has to reprogram the hardware, but that's less 593 * expensive than going through a full hrtimer_interrupt() cycle 594 * for nothing. 595 * 596 * hrtimer_try_to_cancel() is sufficient here as the timer is CPU 597 * local and once the hrtimer code disabled interrupts the timer 598 * callback cannot be running. 599 */ 600 if (st->cookie == current) 601 hrtimer_try_to_cancel(&st->timer); 602 } 603 604 static inline void rseq_slice_set_need_resched(struct task_struct *curr) 605 { 606 /* 607 * The interrupt guard is required to prevent inconsistent state in 608 * this case: 609 * 610 * set_tsk_need_resched() 611 * --> Interrupt 612 * wakeup() 613 * set_tsk_need_resched() 614 * set_preempt_need_resched() 615 * schedule_on_return() 616 * clear_tsk_need_resched() 617 * clear_preempt_need_resched() 618 * set_preempt_need_resched() <- Inconsistent state 619 * 620 * This is safe vs. a remote set of TIF_NEED_RESCHED because that 621 * only sets the already set bit and does not create inconsistent 622 * state. 623 */ 624 scoped_guard(irq) 625 set_need_resched_current(); 626 } 627 628 static void rseq_slice_validate_ctrl(u32 expected) 629 { 630 u32 __user *sctrl = ¤t->rseq.usrptr->slice_ctrl.all; 631 u32 uval; 632 633 if (get_user(uval, sctrl) || uval != expected) 634 force_sig(SIGSEGV); 635 } 636 637 /* 638 * Invoked from syscall entry if a time slice extension was granted and the 639 * kernel did not clear it before user space left the critical section. 640 * 641 * While the recommended way to relinquish the CPU side effect free is 642 * rseq_slice_yield(2), any syscall within a granted slice terminates the 643 * grant and immediately reschedules if required. This supports onion layer 644 * applications, where the code requesting the grant cannot control the 645 * code within the critical section. 646 */ 647 void rseq_syscall_enter_work(long syscall) 648 { 649 struct task_struct *curr = current; 650 struct rseq_slice_ctrl ctrl = { .granted = curr->rseq.slice.state.granted }; 651 652 clear_task_syscall_work(curr, SYSCALL_RSEQ_SLICE); 653 654 if (static_branch_unlikely(&rseq_debug_enabled)) 655 rseq_slice_validate_ctrl(ctrl.all); 656 657 /* 658 * The kernel might have raced, revoked the grant and updated 659 * userspace, but kept the SLICE work set. 660 */ 661 if (!ctrl.granted) 662 return; 663 664 /* 665 * Required to stabilize the per CPU timer pointer and to make 666 * set_tsk_need_resched() correct on PREEMPT[RT] kernels. 667 * 668 * Leaving the scope will reschedule on preemption models FULL, 669 * LAZY and RT if necessary. 670 */ 671 scoped_guard(preempt) { 672 rseq_cancel_slice_extension_timer(); 673 /* 674 * Now that preemption is disabled, quickly check whether 675 * the task was already rescheduled before arriving here. 676 */ 677 if (!curr->rseq.event.sched_switch) { 678 rseq_slice_set_need_resched(curr); 679 680 if (syscall == __NR_rseq_slice_yield) { 681 rseq_stat_inc(rseq_stats.s_yielded); 682 /* Update the yielded state for syscall return */ 683 curr->rseq.slice.yielded = 1; 684 } else { 685 rseq_stat_inc(rseq_stats.s_aborted); 686 } 687 } 688 } 689 /* Reschedule on NONE/VOLUNTARY preemption models */ 690 cond_resched(); 691 692 /* Clear the grant in kernel state and user space */ 693 curr->rseq.slice.state.granted = false; 694 if (put_user(0U, &curr->rseq.usrptr->slice_ctrl.all)) 695 force_sig(SIGSEGV); 696 } 697 698 int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3) 699 { 700 switch (arg2) { 701 case PR_RSEQ_SLICE_EXTENSION_GET: 702 if (arg3) 703 return -EINVAL; 704 return current->rseq.slice.state.enabled ? PR_RSEQ_SLICE_EXT_ENABLE : 0; 705 706 case PR_RSEQ_SLICE_EXTENSION_SET: { 707 u32 rflags, valid = RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE; 708 bool enable = !!(arg3 & PR_RSEQ_SLICE_EXT_ENABLE); 709 710 if (arg3 & ~PR_RSEQ_SLICE_EXT_ENABLE) 711 return -EINVAL; 712 if (!rseq_slice_extension_enabled()) 713 return -ENOTSUPP; 714 if (!current->rseq.usrptr) 715 return -ENXIO; 716 717 /* No change? */ 718 if (enable == !!current->rseq.slice.state.enabled) 719 return 0; 720 721 if (get_user(rflags, ¤t->rseq.usrptr->flags)) 722 goto die; 723 724 if (current->rseq.slice.state.enabled) 725 valid |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED; 726 727 if ((rflags & valid) != valid) 728 goto die; 729 730 rflags &= ~RSEQ_CS_FLAG_SLICE_EXT_ENABLED; 731 rflags |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE; 732 if (enable) 733 rflags |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED; 734 735 if (put_user(rflags, ¤t->rseq.usrptr->flags)) 736 goto die; 737 738 current->rseq.slice.state.enabled = enable; 739 return 0; 740 } 741 default: 742 return -EINVAL; 743 } 744 die: 745 force_sig(SIGSEGV); 746 return -EFAULT; 747 } 748 749 /** 750 * sys_rseq_slice_yield - yield the current processor side effect free if a 751 * task granted with a time slice extension is done with 752 * the critical work before being forced out. 753 * 754 * Return: 1 if the task successfully yielded the CPU within the granted slice. 755 * 0 if the slice extension was either never granted or was revoked by 756 * going over the granted extension, using a syscall other than this one 757 * or being scheduled out earlier due to a subsequent interrupt. 758 * 759 * The syscall does not schedule because the syscall entry work immediately 760 * relinquishes the CPU and schedules if required. 761 */ 762 SYSCALL_DEFINE0(rseq_slice_yield) 763 { 764 int yielded = !!current->rseq.slice.yielded; 765 766 current->rseq.slice.yielded = 0; 767 return yielded; 768 } 769 770 static int rseq_slice_ext_show(struct seq_file *m, void *p) 771 { 772 seq_printf(m, "%d\n", rseq_slice_ext_nsecs); 773 return 0; 774 } 775 776 static ssize_t rseq_slice_ext_write(struct file *file, const char __user *ubuf, 777 size_t count, loff_t *ppos) 778 { 779 unsigned int nsecs; 780 781 if (kstrtouint_from_user(ubuf, count, 10, &nsecs)) 782 return -EINVAL; 783 784 if (nsecs < rseq_slice_ext_nsecs_min) 785 return -ERANGE; 786 787 if (nsecs > rseq_slice_ext_nsecs_max) 788 return -ERANGE; 789 790 rseq_slice_ext_nsecs = nsecs; 791 792 return count; 793 } 794 795 static int rseq_slice_ext_open(struct inode *inode, struct file *file) 796 { 797 return single_open(file, rseq_slice_ext_show, inode->i_private); 798 } 799 800 static const struct file_operations slice_ext_ops = { 801 .open = rseq_slice_ext_open, 802 .read = seq_read, 803 .write = rseq_slice_ext_write, 804 .llseek = seq_lseek, 805 .release = single_release, 806 }; 807 808 static void rseq_slice_ext_init(struct dentry *root_dir) 809 { 810 debugfs_create_file("slice_ext_nsec", 0644, root_dir, NULL, &slice_ext_ops); 811 } 812 813 static int __init rseq_slice_cmdline(char *str) 814 { 815 bool on; 816 817 if (kstrtobool(str, &on)) 818 return 0; 819 820 if (!on) 821 static_branch_disable(&rseq_slice_extension_key); 822 return 1; 823 } 824 __setup("rseq_slice_ext=", rseq_slice_cmdline); 825 826 static int __init rseq_slice_init(void) 827 { 828 unsigned int cpu; 829 830 for_each_possible_cpu(cpu) { 831 hrtimer_setup(per_cpu_ptr(&slice_timer.timer, cpu), rseq_slice_expired, 832 CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED_HARD); 833 } 834 return 0; 835 } 836 device_initcall(rseq_slice_init); 837 #else 838 static void rseq_slice_ext_init(struct dentry *root_dir) { } 839 #endif /* CONFIG_RSEQ_SLICE_EXTENSION */ 840