[linux-block.git] / kernel / rseq.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Restartable sequences system call
 *
 * Copyright (C) 2015, Google, Inc.,
 * Paul Turner <pjt@google.com> and Andrew Hunter <ahh@google.com>
 * Copyright (C) 2015-2018, EfficiOS Inc.,
 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 */

#include <linux/sched.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/rseq.h>
#include <linux/types.h>
#include <asm/ptrace.h>

#define CREATE_TRACE_POINTS
#include <trace/events/rseq.h>

#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \
				  RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \
				  RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE)

/*
 *
 * Restartable sequences are a lightweight interface that allows
 * user-level code to be executed atomically relative to scheduler
 * preemption and signal delivery. Typically used for implementing
 * per-cpu operations.
 *
 * It allows user-space to perform update operations on per-cpu data
 * without requiring heavy-weight atomic operations.
 *
 * Detailed algorithm of rseq user-space assembly sequences:
 *
 *                     init(rseq_cs)
 *                     cpu = TLS->rseq::cpu_id_start
 *   [1]               TLS->rseq::rseq_cs = rseq_cs
 *   [start_ip]        ----------------------------
 *   [2]               if (cpu != TLS->rseq::cpu_id)
 *                             goto abort_ip;
 *   [3]               <last_instruction_in_cs>
 *   [post_commit_ip]  ----------------------------
 *
 *   The address of jump target abort_ip must be outside the critical
 *   region, i.e.:
 *
 *     [abort_ip] < [start_ip]  || [abort_ip] >= [post_commit_ip]
 *
 *   Steps [2]-[3] (inclusive) need to be a sequence of instructions in
 *   userspace that can handle being interrupted between any of those
 *   instructions, and then resumed to the abort_ip.
 *
 *   1.  Userspace stores the address of the struct rseq_cs assembly
 *       block descriptor into the rseq_cs field of the registered
 *       struct rseq TLS area. This update is performed through a single
 *       store within the inline assembly instruction sequence.
 *       [start_ip]
 *
 *   2.  Userspace tests to check whether the current cpu_id field match
 *       the cpu number loaded before start_ip, branching to abort_ip
 *       in case of a mismatch.
 *
 *       If the sequence is preempted or interrupted by a signal
 *       at or after start_ip and before post_commit_ip, then the kernel
 *       clears TLS->__rseq_abi::rseq_cs, and sets the user-space return
 *       ip to abort_ip before returning to user-space, so the preempted
 *       execution resumes at abort_ip.
 *
 *   3.  Userspace critical section final instruction before
 *       post_commit_ip is the commit. The critical section is
 *       self-terminating.
 *       [post_commit_ip]
 *
 *   4.  <success>
 *
 *   On failure at [2], or if interrupted by preempt or signal delivery
 *   between [1] and [3]:
 *
 *       [abort_ip]
 *   F1. <failure>
 */

static int rseq_update_cpu_id(struct task_struct *t)
{
	u32 cpu_id = raw_smp_processor_id();
	struct rseq __user *rseq = t->rseq;

	if (!user_write_access_begin(rseq, sizeof(*rseq)))
		goto efault;
	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
	user_write_access_end();
	trace_rseq_update(t);
	return 0;

efault_end:
	user_write_access_end();
efault:
	return -EFAULT;
}

static int rseq_reset_rseq_cpu_id(struct task_struct *t)
{
	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED;

	/*
	 * Reset cpu_id_start to its initial state (0).
	 */
	if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
		return -EFAULT;
	/*
	 * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming
	 * in after unregistration can figure out that rseq needs to be
	 * registered again.
	 */
	if (put_user(cpu_id, &t->rseq->cpu_id))
		return -EFAULT;
	return 0;
}

static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
{
	struct rseq_cs __user *urseq_cs;
	u64 ptr;
	u32 __user *usig;
	u32 sig;
	int ret;

#ifdef CONFIG_64BIT
	if (get_user(ptr, &t->rseq->rseq_cs))
		return -EFAULT;
#else
	if (copy_from_user(&ptr, &t->rseq->rseq_cs, sizeof(ptr)))
		return -EFAULT;
#endif
	if (!ptr) {
		memset(rseq_cs, 0, sizeof(*rseq_cs));
		return 0;
	}
	if (ptr >= TASK_SIZE)
		return -EINVAL;
	urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
	if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
		return -EFAULT;

	if (rseq_cs->start_ip >= TASK_SIZE ||
	    rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
	    rseq_cs->abort_ip >= TASK_SIZE ||
	    rseq_cs->version > 0)
		return -EINVAL;
	/* Check for overflow. */
	if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)
		return -EINVAL;
	/* Ensure that abort_ip is not in the critical section. */
	if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
		return -EINVAL;

	usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
	ret = get_user(sig, usig);
	if (ret)
		return ret;

	if (current->rseq_sig != sig) {
		printk_ratelimited(KERN_WARNING
			"Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
			sig, current->rseq_sig, current->pid, usig);
		return -EINVAL;
	}
	return 0;
}

static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
{
	u32 flags, event_mask;
	int ret;

	if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS) || cs_flags)
		return -EINVAL;

	/* Get thread flags. */
	ret = get_user(flags, &t->rseq->flags);
	if (ret)
		return ret;

	if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS) || flags)
		return -EINVAL;

	/*
	 * Load and clear event mask atomically with respect to
	 * scheduler preemption.
	 */
	preempt_disable();
	event_mask = t->rseq_event_mask;
	t->rseq_event_mask = 0;
	preempt_enable();

	return !!event_mask;
}

static int clear_rseq_cs(struct task_struct *t)
{
	/*
	 * The rseq_cs field is set to NULL on preemption or signal
	 * delivery on top of rseq assembly block, as well as on top
	 * of code outside of the rseq assembly block. This performs
	 * a lazy clear of the rseq_cs field.
	 *
	 * Set rseq_cs to NULL.
	 */
#ifdef CONFIG_64BIT
	return put_user(0UL, &t->rseq->rseq_cs);
#else
	if (clear_user(&t->rseq->rseq_cs, sizeof(t->rseq->rseq_cs)))
		return -EFAULT;
	return 0;
#endif
}

/*
 * Unsigned comparison will be true when ip >= start_ip, and when
 * ip < start_ip + post_commit_offset.
 */
static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs)
{
	return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset;
}

static int rseq_ip_fixup(struct pt_regs *regs)
{
	unsigned long ip = instruction_pointer(regs);
	struct task_struct *t = current;
	struct rseq_cs rseq_cs;
	int ret;

	ret = rseq_get_rseq_cs(t, &rseq_cs);
	if (ret)
		return ret;

	/*
	 * Handle potentially not being within a critical section.
	 * If not nested over a rseq critical section, restart is useless.
	 * Clear the rseq_cs pointer and return.
	 */
	if (!in_rseq_cs(ip, &rseq_cs))
		return clear_rseq_cs(t);
	ret = rseq_need_restart(t, rseq_cs.flags);
	if (ret <= 0)
		return ret;
	ret = clear_rseq_cs(t);
	if (ret)
		return ret;
	trace_rseq_ip_fixup(ip, rseq_cs.start_ip, rseq_cs.post_commit_offset,
			    rseq_cs.abort_ip);
	instruction_pointer_set(regs, (unsigned long)rseq_cs.abort_ip);
	return 0;
}

/*
 * This resume handler must always be executed between any of:
 * - preemption,
 * - signal delivery,
 * and return to user-space.
 *
 * This is how we can ensure that the entire rseq critical section
 * will issue the commit instruction only if executed atomically with
 * respect to other threads scheduled on the same CPU, and with respect
 * to signal handlers.
 */
void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
{
	struct task_struct *t = current;
	int ret, sig;

	if (unlikely(t->flags & PF_EXITING))
		return;

	/*
	 * regs is NULL if and only if the caller is in a syscall path.  Skip
	 * fixup and leave rseq_cs as is so that rseq_sycall() will detect and
	 * kill a misbehaving userspace on debug kernels.
	 */
	if (regs) {
		ret = rseq_ip_fixup(regs);
		if (unlikely(ret < 0))
			goto error;
	}
	if (unlikely(rseq_update_cpu_id(t)))
		goto error;
	return;

error:
	sig = ksig ? ksig->sig : 0;
	force_sigsegv(sig);
}

#ifdef CONFIG_DEBUG_RSEQ

/*
 * Terminate the process if a syscall is issued within a restartable
 * sequence.
 */
void rseq_syscall(struct pt_regs *regs)
{
	unsigned long ip = instruction_pointer(regs);
	struct task_struct *t = current;
	struct rseq_cs rseq_cs;

	if (!t->rseq)
		return;
	if (rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
		force_sig(SIGSEGV);
}

#endif

/*
 * sys_rseq - setup restartable sequences for caller thread.
 */
SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
		int, flags, u32, sig)
{
	int ret;

	if (flags & RSEQ_FLAG_UNREGISTER) {
		if (flags & ~RSEQ_FLAG_UNREGISTER)
			return -EINVAL;
		/* Unregister rseq for current thread. */
		if (current->rseq != rseq || !current->rseq)
			return -EINVAL;
		if (rseq_len != sizeof(*rseq))
			return -EINVAL;
		if (current->rseq_sig != sig)
			return -EPERM;
		ret = rseq_reset_rseq_cpu_id(current);
		if (ret)
			return ret;
		current->rseq = NULL;
		current->rseq_sig = 0;
		return 0;
	}

	if (unlikely(flags))
		return -EINVAL;

	if (current->rseq) {
		/*
		 * If rseq is already registered, check whether
		 * the provided address differs from the prior
		 * one.
		 */
		if (current->rseq != rseq || rseq_len != sizeof(*rseq))
			return -EINVAL;
		if (current->rseq_sig != sig)
			return -EPERM;
		/* Already registered. */
		return -EBUSY;
	}

	/*
	 * If there was no rseq previously registered,
	 * ensure the provided rseq is properly aligned and valid.
	 */
	if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) ||
	    rseq_len != sizeof(*rseq))
		return -EINVAL;
	if (!access_ok(rseq, rseq_len))
		return -EFAULT;
	current->rseq = rseq;
	current->rseq_sig = sig;
	/*
	 * If rseq was previously inactive, and has just been
	 * registered, ensure the cpu_id_start and cpu_id fields
	 * are updated before returning to user-space.
	 */
	rseq_set_notify_resume(current);

	return 0;
}
Commit	Line	Data
d7822b1e MD	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
0190e419 MD	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)
d7822b1e MD	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
	85	static int rseq_update_cpu_id(struct task_struct *t)
	86	{
	87	u32 cpu_id = raw_smp_processor_id();
60af388d	88	struct rseq __user *rseq = t->rseq;
d7822b1e	89
60af388d ED	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();
d7822b1e MD	95	trace_rseq_update(t);
d7822b1e MD	96	return 0;
60af388d ED	97
	98	efault_end:
	99	user_write_access_end();
	100	efault:
	101	return -EFAULT;
d7822b1e MD	102	}
	103
	104	static 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	*/
8f281770	111	if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
d7822b1e MD	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	*/
8f281770	118	if (put_user(cpu_id, &t->rseq->cpu_id))
d7822b1e MD	119	return -EFAULT;
	120	return 0;
	121	}
	122
	123	static int rseq_get_rseq_cs(struct task_struct t, struct rseq_cs rseq_cs)
	124	{
	125	struct rseq_cs __user *urseq_cs;
ec9c82e0	126	u64 ptr;
d7822b1e MD	127	u32 __user *usig;
	128	u32 sig;
	129	int ret;
	130
5e0ccd4a	131	#ifdef CONFIG_64BIT
bfdf4e62	132	if (get_user(ptr, &t->rseq->rseq_cs))
5e0ccd4a ED	133	return -EFAULT;
5e0ccd4a ED	134	#else
bfdf4e62	135	if (copy_from_user(&ptr, &t->rseq->rseq_cs, sizeof(ptr)))
ec9c82e0	136	return -EFAULT;
5e0ccd4a	137	#endif
d7822b1e MD	138	if (!ptr) {
	139	memset(rseq_cs, 0, sizeof(*rseq_cs));
	140	return 0;
	141	}
ec9c82e0 MD	142	if (ptr >= TASK_SIZE)
	143	return -EINVAL;
	144	urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
d7822b1e MD	145	if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
d7822b1e MD	146	return -EFAULT;
d7822b1e	147
e96d7135 MD	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;
d7822b1e MD	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
e96d7135	160	usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
d7822b1e MD	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);
e96d7135	169	return -EINVAL;
d7822b1e MD	170	}
	171	return 0;
	172	}
	173
	174	static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
	175	{
	176	u32 flags, event_mask;
	177	int ret;
	178
c17a6ff9	179	if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS) \|\| cs_flags)
0190e419 MD	180	return -EINVAL;
0190e419 MD	181
d7822b1e	182	/* Get thread flags. */
8f281770	183	ret = get_user(flags, &t->rseq->flags);
d7822b1e MD	184	if (ret)
	185	return ret;
	186
c17a6ff9	187	if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS) \|\| flags)
d7822b1e MD	188	return -EINVAL;
	189
	190	/*
	191	* Load and clear event mask atomically with respect to
	192	* scheduler preemption.
	193	*/
	194	preempt_disable();
	195	event_mask = t->rseq_event_mask;
	196	t->rseq_event_mask = 0;
	197	preempt_enable();
	198
0190e419	199	return !!event_mask;
d7822b1e MD	200	}
	201
	202	static int clear_rseq_cs(struct task_struct *t)
	203	{
	204	/*
	205	* The rseq_cs field is set to NULL on preemption or signal
	206	* delivery on top of rseq assembly block, as well as on top
	207	* of code outside of the rseq assembly block. This performs
	208	* a lazy clear of the rseq_cs field.
	209	*
0fb9a1ab	210	* Set rseq_cs to NULL.
d7822b1e	211	*/
5e0ccd4a	212	#ifdef CONFIG_64BIT
bfdf4e62	213	return put_user(0UL, &t->rseq->rseq_cs);
5e0ccd4a	214	#else
bfdf4e62	215	if (clear_user(&t->rseq->rseq_cs, sizeof(t->rseq->rseq_cs)))
ec9c82e0 MD	216	return -EFAULT;
ec9c82e0 MD	217	return 0;
5e0ccd4a	218	#endif
d7822b1e MD	219	}
	220
	221	/*
	222	* Unsigned comparison will be true when ip >= start_ip, and when
	223	* ip < start_ip + post_commit_offset.
	224	*/
	225	static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs)
	226	{
	227	return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset;
	228	}
	229
	230	static int rseq_ip_fixup(struct pt_regs *regs)
	231	{
	232	unsigned long ip = instruction_pointer(regs);
	233	struct task_struct *t = current;
	234	struct rseq_cs rseq_cs;
	235	int ret;
	236
	237	ret = rseq_get_rseq_cs(t, &rseq_cs);
	238	if (ret)
	239	return ret;
	240
	241	/*
	242	* Handle potentially not being within a critical section.
	243	* If not nested over a rseq critical section, restart is useless.
	244	* Clear the rseq_cs pointer and return.
	245	*/
	246	if (!in_rseq_cs(ip, &rseq_cs))
	247	return clear_rseq_cs(t);
	248	ret = rseq_need_restart(t, rseq_cs.flags);
	249	if (ret <= 0)
	250	return ret;
	251	ret = clear_rseq_cs(t);
	252	if (ret)
	253	return ret;
	254	trace_rseq_ip_fixup(ip, rseq_cs.start_ip, rseq_cs.post_commit_offset,
	255	rseq_cs.abort_ip);
	256	instruction_pointer_set(regs, (unsigned long)rseq_cs.abort_ip);
	257	return 0;
	258	}
	259
	260	/*
	261	* This resume handler must always be executed between any of:
	262	* - preemption,
	263	* - signal delivery,
	264	* and return to user-space.
	265	*
bff9504b	266	* This is how we can ensure that the entire rseq critical section
d7822b1e MD	267	* will issue the commit instruction only if executed atomically with
	268	* respect to other threads scheduled on the same CPU, and with respect
	269	* to signal handlers.
	270	*/
784e0300	271	void __rseq_handle_notify_resume(struct ksignal ksig, struct pt_regs regs)
d7822b1e MD	272	{
d7822b1e MD	273	struct task_struct *t = current;
784e0300	274	int ret, sig;
d7822b1e MD	275
	276	if (unlikely(t->flags & PF_EXITING))
	277	return;
8646e536 SC	278
	279	/*
	280	* regs is NULL if and only if the caller is in a syscall path. Skip
	281	* fixup and leave rseq_cs as is so that rseq_sycall() will detect and
	282	* kill a misbehaving userspace on debug kernels.
	283	*/
	284	if (regs) {
	285	ret = rseq_ip_fixup(regs);
	286	if (unlikely(ret < 0))
	287	goto error;
	288	}
d7822b1e MD	289	if (unlikely(rseq_update_cpu_id(t)))
	290	goto error;
	291	return;
	292
	293	error:
784e0300	294	sig = ksig ? ksig->sig : 0;
cb44c9a0	295	force_sigsegv(sig);
d7822b1e MD	296	}
	297
	298	#ifdef CONFIG_DEBUG_RSEQ
	299
	300	/*
	301	* Terminate the process if a syscall is issued within a restartable
	302	* sequence.
	303	*/
	304	void rseq_syscall(struct pt_regs *regs)
	305	{
	306	unsigned long ip = instruction_pointer(regs);
	307	struct task_struct *t = current;
	308	struct rseq_cs rseq_cs;
	309
	310	if (!t->rseq)
	311	return;
0ed96051	312	if (rseq_get_rseq_cs(t, &rseq_cs) \|\| in_rseq_cs(ip, &rseq_cs))
3cf5d076	313	force_sig(SIGSEGV);
d7822b1e MD	314	}
	315
	316	#endif
	317
	318	/*
	319	* sys_rseq - setup restartable sequences for caller thread.
	320	*/
	321	SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
	322	int, flags, u32, sig)
	323	{
	324	int ret;
	325
	326	if (flags & RSEQ_FLAG_UNREGISTER) {
66528a45 MD	327	if (flags & ~RSEQ_FLAG_UNREGISTER)
66528a45 MD	328	return -EINVAL;
d7822b1e MD	329	/* Unregister rseq for current thread. */
	330	if (current->rseq != rseq \|\| !current->rseq)
	331	return -EINVAL;
83b0b15b	332	if (rseq_len != sizeof(*rseq))
d7822b1e MD	333	return -EINVAL;
	334	if (current->rseq_sig != sig)
	335	return -EPERM;
	336	ret = rseq_reset_rseq_cpu_id(current);
	337	if (ret)
	338	return ret;
	339	current->rseq = NULL;
d7822b1e MD	340	current->rseq_sig = 0;
	341	return 0;
	342	}
	343
	344	if (unlikely(flags))
	345	return -EINVAL;
	346
	347	if (current->rseq) {
	348	/*
	349	* If rseq is already registered, check whether
	350	* the provided address differs from the prior
	351	* one.
	352	*/
83b0b15b	353	if (current->rseq != rseq \|\| rseq_len != sizeof(*rseq))
d7822b1e MD	354	return -EINVAL;
	355	if (current->rseq_sig != sig)
	356	return -EPERM;
	357	/* Already registered. */
	358	return -EBUSY;
	359	}
	360
	361	/*
	362	* If there was no rseq previously registered,
	363	* ensure the provided rseq is properly aligned and valid.
	364	*/
	365	if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) \|\|
	366	rseq_len != sizeof(*rseq))
	367	return -EINVAL;
96d4f267	368	if (!access_ok(rseq, rseq_len))
d7822b1e MD	369	return -EFAULT;
d7822b1e MD	370	current->rseq = rseq;
d7822b1e MD	371	current->rseq_sig = sig;
	372	/*
	373	* If rseq was previously inactive, and has just been
	374	* registered, ensure the cpu_id_start and cpu_id fields
	375	* are updated before returning to user-space.
	376	*/
	377	rseq_set_notify_resume(current);
	378
	379	return 0;
	380	}