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v6.9.4
  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#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 padding) is 32 bytes. */
 22#define ORIG_RSEQ_SIZE		32
 23
 24#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \
 25				  RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \
 26				  RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE)
 27
 28/*
 29 *
 30 * Restartable sequences are a lightweight interface that allows
 31 * user-level code to be executed atomically relative to scheduler
 32 * preemption and signal delivery. Typically used for implementing
 33 * per-cpu operations.
 34 *
 35 * It allows user-space to perform update operations on per-cpu data
 36 * without requiring heavy-weight atomic operations.
 37 *
 38 * Detailed algorithm of rseq user-space assembly sequences:
 39 *
 40 *                     init(rseq_cs)
 41 *                     cpu = TLS->rseq::cpu_id_start
 42 *   [1]               TLS->rseq::rseq_cs = rseq_cs
 43 *   [start_ip]        ----------------------------
 44 *   [2]               if (cpu != TLS->rseq::cpu_id)
 45 *                             goto abort_ip;
 46 *   [3]               <last_instruction_in_cs>
 47 *   [post_commit_ip]  ----------------------------
 48 *
 49 *   The address of jump target abort_ip must be outside the critical
 50 *   region, i.e.:
 51 *
 52 *     [abort_ip] < [start_ip]  || [abort_ip] >= [post_commit_ip]
 53 *
 54 *   Steps [2]-[3] (inclusive) need to be a sequence of instructions in
 55 *   userspace that can handle being interrupted between any of those
 56 *   instructions, and then resumed to the abort_ip.
 57 *
 58 *   1.  Userspace stores the address of the struct rseq_cs assembly
 59 *       block descriptor into the rseq_cs field of the registered
 60 *       struct rseq TLS area. This update is performed through a single
 61 *       store within the inline assembly instruction sequence.
 62 *       [start_ip]
 63 *
 64 *   2.  Userspace tests to check whether the current cpu_id field match
 65 *       the cpu number loaded before start_ip, branching to abort_ip
 66 *       in case of a mismatch.
 67 *
 68 *       If the sequence is preempted or interrupted by a signal
 69 *       at or after start_ip and before post_commit_ip, then the kernel
 70 *       clears TLS->__rseq_abi::rseq_cs, and sets the user-space return
 71 *       ip to abort_ip before returning to user-space, so the preempted
 72 *       execution resumes at abort_ip.
 73 *
 74 *   3.  Userspace critical section final instruction before
 75 *       post_commit_ip is the commit. The critical section is
 76 *       self-terminating.
 77 *       [post_commit_ip]
 78 *
 79 *   4.  <success>
 80 *
 81 *   On failure at [2], or if interrupted by preempt or signal delivery
 82 *   between [1] and [3]:
 83 *
 84 *       [abort_ip]
 85 *   F1. <failure>
 86 */
 87
 88static int rseq_update_cpu_node_id(struct task_struct *t)
 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->rseq_len))
 97		goto efault;
 98	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
 99	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
100	unsafe_put_user(node_id, &rseq->node_id, efault_end);
101	unsafe_put_user(mm_cid, &rseq->mm_cid, efault_end);
102	/*
103	 * Additional feature fields added after ORIG_RSEQ_SIZE
104	 * need to be conditionally updated only if
105	 * t->rseq_len != ORIG_RSEQ_SIZE.
106	 */
107	user_write_access_end();
108	trace_rseq_update(t);
109	return 0;
110
111efault_end:
112	user_write_access_end();
113efault:
114	return -EFAULT;
115}
116
117static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
118{
119	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0,
120	    mm_cid = 0;
121
122	/*
123	 * Reset cpu_id_start to its initial state (0).
124	 */
125	if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
126		return -EFAULT;
127	/*
128	 * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming
129	 * in after unregistration can figure out that rseq needs to be
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 (0).
136	 */
137	if (put_user(node_id, &t->rseq->node_id))
138		return -EFAULT;
139	/*
140	 * Reset mm_cid to its initial state (0).
141	 */
142	if (put_user(mm_cid, &t->rseq->mm_cid))
143		return -EFAULT;
144	/*
145	 * Additional feature fields added after ORIG_RSEQ_SIZE
146	 * need to be conditionally reset only if
147	 * t->rseq_len != ORIG_RSEQ_SIZE.
148	 */
149	return 0;
150}
151
152static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
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->rseq_cs, sizeof(ptr)))
165		return -EFAULT;
166#endif
167	if (!ptr) {
168		memset(rseq_cs, 0, sizeof(*rseq_cs));
169		return 0;
170	}
171	if (ptr >= TASK_SIZE)
172		return -EINVAL;
173	urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
174	if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
175		return -EFAULT;
176
177	if (rseq_cs->start_ip >= TASK_SIZE ||
178	    rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
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_commit_offset < rseq_cs->start_ip)
184		return -EINVAL;
185	/* Ensure that abort_ip is not in the critical section. */
186	if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
187		return -EINVAL;
188
189	usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
190	ret = get_user(sig, usig);
191	if (ret)
192		return ret;
193
194	if (current->rseq_sig != sig) {
195		printk_ratelimited(KERN_WARNING
196			"Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
197			sig, current->rseq_sig, current->pid, usig);
198		return -EINVAL;
199	}
200	return 0;
201}
202
203static bool rseq_warn_flags(const char *str, u32 flags)
204{
205	u32 test_flags;
206
207	if (!flags)
208		return false;
209	test_flags = flags & RSEQ_CS_NO_RESTART_FLAGS;
210	if (test_flags)
211		pr_warn_once("Deprecated flags (%u) in %s ABI structure", test_flags, str);
212	test_flags = flags & ~RSEQ_CS_NO_RESTART_FLAGS;
213	if (test_flags)
214		pr_warn_once("Unknown flags (%u) in %s ABI structure", test_flags, str);
215	return true;
216}
217
218static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
219{
220	u32 flags, event_mask;
221	int ret;
222
223	if (rseq_warn_flags("rseq_cs", cs_flags))
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 atomically with respect to
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
246static int clear_rseq_cs(struct task_struct *t)
247{
248	/*
249	 * The rseq_cs field is set to NULL on preemption or signal
250	 * delivery on top of rseq assembly block, as well as on top
251	 * of code outside of the rseq assembly block. This performs
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, sizeof(t->rseq->rseq_cs)))
260		return -EFAULT;
261	return 0;
262#endif
263}
264
265/*
266 * Unsigned comparison will be true when ip >= start_ip, and when
267 * ip < start_ip + post_commit_offset.
268 */
269static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs)
270{
271	return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset;
272}
273
274static int rseq_ip_fixup(struct pt_regs *regs)
275{
276	unsigned long ip = instruction_pointer(regs);
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 a critical section.
287	 * If not nested over a rseq critical section, restart is useless.
288	 * Clear the rseq_cs pointer and return.
289	 */
290	if (!in_rseq_cs(ip, &rseq_cs))
291		return clear_rseq_cs(t);
292	ret = rseq_need_restart(t, rseq_cs.flags);
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_ip, rseq_cs.post_commit_offset,
299			    rseq_cs.abort_ip);
300	instruction_pointer_set(regs, (unsigned long)rseq_cs.abort_ip);
301	return 0;
302}
303
304/*
305 * This resume handler must always be executed between any of:
306 * - preemption,
307 * - signal delivery,
308 * and return to user-space.
309 *
310 * This is how we can ensure that the entire rseq critical section
311 * will issue the commit instruction only if executed atomically with
312 * respect to other threads scheduled on the same CPU, and with respect
313 * to signal handlers.
314 */
315void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
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 caller is in a syscall path.  Skip
325	 * fixup and leave rseq_cs as is so that rseq_sycall() will detect and
326	 * kill a misbehaving userspace on debug kernels.
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
337error:
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 issued within a restartable
346 * sequence.
347 */
348void rseq_syscall(struct pt_regs *regs)
349{
350	unsigned long ip = instruction_pointer(regs);
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) || in_rseq_cs(ip, &rseq_cs))
357		force_sig(SIGSEGV);
358}
359
360#endif
361
362/*
363 * sys_rseq - setup restartable sequences for caller thread.
364 */
365SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
366		int, flags, u32, sig)
367{
368	int ret;
369
370	if (flags & RSEQ_FLAG_UNREGISTER) {
371		if (flags & ~RSEQ_FLAG_UNREGISTER)
372			return -EINVAL;
373		/* Unregister rseq for current thread. */
374		if (current->rseq != rseq || !current->rseq)
375			return -EINVAL;
376		if (rseq_len != current->rseq_len)
377			return -EINVAL;
378		if (current->rseq_sig != sig)
379			return -EPERM;
380		ret = rseq_reset_rseq_cpu_node_id(current);
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 registered, check whether
395		 * the provided address differs from the prior
396		 * one.
397		 */
398		if (current->rseq != rseq || rseq_len != current->rseq_len)
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 registered, ensure the provided rseq
408	 * is properly aligned, as communcated to user-space through the ELF
409	 * auxiliary vector AT_RSEQ_ALIGN. If rseq_len is the original rseq
410	 * size, the required alignment is the original struct rseq alignment.
411	 *
412	 * In order to be valid, rseq_len is either the original rseq size, or
413	 * large enough to contain all supported fields, as communicated to
414	 * user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE.
415	 */
416	if (rseq_len < ORIG_RSEQ_SIZE ||
417	    (rseq_len == ORIG_RSEQ_SIZE && !IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE)) ||
418	    (rseq_len != ORIG_RSEQ_SIZE && (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) ||
419					    rseq_len < offsetof(struct rseq, end))))
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, and has just been
428	 * registered, ensure the cpu_id_start and cpu_id fields
429	 * are updated before returning to user-space.
430	 */
431	rseq_set_notify_resume(current);
432
433	return 0;
434}
v6.2
  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#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#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \
 22				  RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \
 23				  RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE)
 24
 25/*
 26 *
 27 * Restartable sequences are a lightweight interface that allows
 28 * user-level code to be executed atomically relative to scheduler
 29 * preemption and signal delivery. Typically used for implementing
 30 * per-cpu operations.
 31 *
 32 * It allows user-space to perform update operations on per-cpu data
 33 * without requiring heavy-weight atomic operations.
 34 *
 35 * Detailed algorithm of rseq user-space assembly sequences:
 36 *
 37 *                     init(rseq_cs)
 38 *                     cpu = TLS->rseq::cpu_id_start
 39 *   [1]               TLS->rseq::rseq_cs = rseq_cs
 40 *   [start_ip]        ----------------------------
 41 *   [2]               if (cpu != TLS->rseq::cpu_id)
 42 *                             goto abort_ip;
 43 *   [3]               <last_instruction_in_cs>
 44 *   [post_commit_ip]  ----------------------------
 45 *
 46 *   The address of jump target abort_ip must be outside the critical
 47 *   region, i.e.:
 48 *
 49 *     [abort_ip] < [start_ip]  || [abort_ip] >= [post_commit_ip]
 50 *
 51 *   Steps [2]-[3] (inclusive) need to be a sequence of instructions in
 52 *   userspace that can handle being interrupted between any of those
 53 *   instructions, and then resumed to the abort_ip.
 54 *
 55 *   1.  Userspace stores the address of the struct rseq_cs assembly
 56 *       block descriptor into the rseq_cs field of the registered
 57 *       struct rseq TLS area. This update is performed through a single
 58 *       store within the inline assembly instruction sequence.
 59 *       [start_ip]
 60 *
 61 *   2.  Userspace tests to check whether the current cpu_id field match
 62 *       the cpu number loaded before start_ip, branching to abort_ip
 63 *       in case of a mismatch.
 64 *
 65 *       If the sequence is preempted or interrupted by a signal
 66 *       at or after start_ip and before post_commit_ip, then the kernel
 67 *       clears TLS->__rseq_abi::rseq_cs, and sets the user-space return
 68 *       ip to abort_ip before returning to user-space, so the preempted
 69 *       execution resumes at abort_ip.
 70 *
 71 *   3.  Userspace critical section final instruction before
 72 *       post_commit_ip is the commit. The critical section is
 73 *       self-terminating.
 74 *       [post_commit_ip]
 75 *
 76 *   4.  <success>
 77 *
 78 *   On failure at [2], or if interrupted by preempt or signal delivery
 79 *   between [1] and [3]:
 80 *
 81 *       [abort_ip]
 82 *   F1. <failure>
 83 */
 84
 85static int rseq_update_cpu_id(struct task_struct *t)
 86{
 
 87	u32 cpu_id = raw_smp_processor_id();
 88	struct rseq __user *rseq = t->rseq;
 
 89
 90	if (!user_write_access_begin(rseq, sizeof(*rseq)))
 
 91		goto efault;
 92	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
 93	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
 
 
 
 
 
 
 
 94	user_write_access_end();
 95	trace_rseq_update(t);
 96	return 0;
 97
 98efault_end:
 99	user_write_access_end();
100efault:
101	return -EFAULT;
102}
103
104static int rseq_reset_rseq_cpu_id(struct task_struct *t)
105{
106	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED;
 
107
108	/*
109	 * Reset cpu_id_start to its initial state (0).
110	 */
111	if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
112		return -EFAULT;
113	/*
114	 * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming
115	 * in after unregistration can figure out that rseq needs to be
116	 * registered again.
117	 */
118	if (put_user(cpu_id, &t->rseq->cpu_id))
119		return -EFAULT;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
120	return 0;
121}
122
123static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
124{
125	struct rseq_cs __user *urseq_cs;
126	u64 ptr;
127	u32 __user *usig;
128	u32 sig;
129	int ret;
130
131#ifdef CONFIG_64BIT
132	if (get_user(ptr, &t->rseq->rseq_cs))
133		return -EFAULT;
134#else
135	if (copy_from_user(&ptr, &t->rseq->rseq_cs, sizeof(ptr)))
136		return -EFAULT;
137#endif
138	if (!ptr) {
139		memset(rseq_cs, 0, sizeof(*rseq_cs));
140		return 0;
141	}
142	if (ptr >= TASK_SIZE)
143		return -EINVAL;
144	urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
145	if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
146		return -EFAULT;
147
148	if (rseq_cs->start_ip >= TASK_SIZE ||
149	    rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
150	    rseq_cs->abort_ip >= TASK_SIZE ||
151	    rseq_cs->version > 0)
152		return -EINVAL;
153	/* Check for overflow. */
154	if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)
155		return -EINVAL;
156	/* Ensure that abort_ip is not in the critical section. */
157	if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
158		return -EINVAL;
159
160	usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
161	ret = get_user(sig, usig);
162	if (ret)
163		return ret;
164
165	if (current->rseq_sig != sig) {
166		printk_ratelimited(KERN_WARNING
167			"Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
168			sig, current->rseq_sig, current->pid, usig);
169		return -EINVAL;
170	}
171	return 0;
172}
173
174static bool rseq_warn_flags(const char *str, u32 flags)
175{
176	u32 test_flags;
177
178	if (!flags)
179		return false;
180	test_flags = flags & RSEQ_CS_NO_RESTART_FLAGS;
181	if (test_flags)
182		pr_warn_once("Deprecated flags (%u) in %s ABI structure", test_flags, str);
183	test_flags = flags & ~RSEQ_CS_NO_RESTART_FLAGS;
184	if (test_flags)
185		pr_warn_once("Unknown flags (%u) in %s ABI structure", test_flags, str);
186	return true;
187}
188
189static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
190{
191	u32 flags, event_mask;
192	int ret;
193
194	if (rseq_warn_flags("rseq_cs", cs_flags))
195		return -EINVAL;
196
197	/* Get thread flags. */
198	ret = get_user(flags, &t->rseq->flags);
199	if (ret)
200		return ret;
201
202	if (rseq_warn_flags("rseq", flags))
203		return -EINVAL;
204
205	/*
206	 * Load and clear event mask atomically with respect to
207	 * scheduler preemption.
208	 */
209	preempt_disable();
210	event_mask = t->rseq_event_mask;
211	t->rseq_event_mask = 0;
212	preempt_enable();
213
214	return !!event_mask;
215}
216
217static int clear_rseq_cs(struct task_struct *t)
218{
219	/*
220	 * The rseq_cs field is set to NULL on preemption or signal
221	 * delivery on top of rseq assembly block, as well as on top
222	 * of code outside of the rseq assembly block. This performs
223	 * a lazy clear of the rseq_cs field.
224	 *
225	 * Set rseq_cs to NULL.
226	 */
227#ifdef CONFIG_64BIT
228	return put_user(0UL, &t->rseq->rseq_cs);
229#else
230	if (clear_user(&t->rseq->rseq_cs, sizeof(t->rseq->rseq_cs)))
231		return -EFAULT;
232	return 0;
233#endif
234}
235
236/*
237 * Unsigned comparison will be true when ip >= start_ip, and when
238 * ip < start_ip + post_commit_offset.
239 */
240static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs)
241{
242	return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset;
243}
244
245static int rseq_ip_fixup(struct pt_regs *regs)
246{
247	unsigned long ip = instruction_pointer(regs);
248	struct task_struct *t = current;
249	struct rseq_cs rseq_cs;
250	int ret;
251
252	ret = rseq_get_rseq_cs(t, &rseq_cs);
253	if (ret)
254		return ret;
255
256	/*
257	 * Handle potentially not being within a critical section.
258	 * If not nested over a rseq critical section, restart is useless.
259	 * Clear the rseq_cs pointer and return.
260	 */
261	if (!in_rseq_cs(ip, &rseq_cs))
262		return clear_rseq_cs(t);
263	ret = rseq_need_restart(t, rseq_cs.flags);
264	if (ret <= 0)
265		return ret;
266	ret = clear_rseq_cs(t);
267	if (ret)
268		return ret;
269	trace_rseq_ip_fixup(ip, rseq_cs.start_ip, rseq_cs.post_commit_offset,
270			    rseq_cs.abort_ip);
271	instruction_pointer_set(regs, (unsigned long)rseq_cs.abort_ip);
272	return 0;
273}
274
275/*
276 * This resume handler must always be executed between any of:
277 * - preemption,
278 * - signal delivery,
279 * and return to user-space.
280 *
281 * This is how we can ensure that the entire rseq critical section
282 * will issue the commit instruction only if executed atomically with
283 * respect to other threads scheduled on the same CPU, and with respect
284 * to signal handlers.
285 */
286void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
287{
288	struct task_struct *t = current;
289	int ret, sig;
290
291	if (unlikely(t->flags & PF_EXITING))
292		return;
293
294	/*
295	 * regs is NULL if and only if the caller is in a syscall path.  Skip
296	 * fixup and leave rseq_cs as is so that rseq_sycall() will detect and
297	 * kill a misbehaving userspace on debug kernels.
298	 */
299	if (regs) {
300		ret = rseq_ip_fixup(regs);
301		if (unlikely(ret < 0))
302			goto error;
303	}
304	if (unlikely(rseq_update_cpu_id(t)))
305		goto error;
306	return;
307
308error:
309	sig = ksig ? ksig->sig : 0;
310	force_sigsegv(sig);
311}
312
313#ifdef CONFIG_DEBUG_RSEQ
314
315/*
316 * Terminate the process if a syscall is issued within a restartable
317 * sequence.
318 */
319void rseq_syscall(struct pt_regs *regs)
320{
321	unsigned long ip = instruction_pointer(regs);
322	struct task_struct *t = current;
323	struct rseq_cs rseq_cs;
324
325	if (!t->rseq)
326		return;
327	if (rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
328		force_sig(SIGSEGV);
329}
330
331#endif
332
333/*
334 * sys_rseq - setup restartable sequences for caller thread.
335 */
336SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
337		int, flags, u32, sig)
338{
339	int ret;
340
341	if (flags & RSEQ_FLAG_UNREGISTER) {
342		if (flags & ~RSEQ_FLAG_UNREGISTER)
343			return -EINVAL;
344		/* Unregister rseq for current thread. */
345		if (current->rseq != rseq || !current->rseq)
346			return -EINVAL;
347		if (rseq_len != sizeof(*rseq))
348			return -EINVAL;
349		if (current->rseq_sig != sig)
350			return -EPERM;
351		ret = rseq_reset_rseq_cpu_id(current);
352		if (ret)
353			return ret;
354		current->rseq = NULL;
355		current->rseq_sig = 0;
 
356		return 0;
357	}
358
359	if (unlikely(flags))
360		return -EINVAL;
361
362	if (current->rseq) {
363		/*
364		 * If rseq is already registered, check whether
365		 * the provided address differs from the prior
366		 * one.
367		 */
368		if (current->rseq != rseq || rseq_len != sizeof(*rseq))
369			return -EINVAL;
370		if (current->rseq_sig != sig)
371			return -EPERM;
372		/* Already registered. */
373		return -EBUSY;
374	}
375
376	/*
377	 * If there was no rseq previously registered,
378	 * ensure the provided rseq is properly aligned and valid.
 
 
 
 
 
 
379	 */
380	if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) ||
381	    rseq_len != sizeof(*rseq))
 
 
382		return -EINVAL;
383	if (!access_ok(rseq, rseq_len))
384		return -EFAULT;
385	current->rseq = rseq;
 
386	current->rseq_sig = sig;
387	/*
388	 * If rseq was previously inactive, and has just been
389	 * registered, ensure the cpu_id_start and cpu_id fields
390	 * are updated before returning to user-space.
391	 */
392	rseq_set_notify_resume(current);
393
394	return 0;
395}