[deliverable/linux.git] / arch / x86 / entry / common.c

/*
 * common.c - C code for kernel entry and exit
 * Copyright (c) 2015 Andrew Lutomirski
 * GPL v2
 *
 * Based on asm and ptrace code by many authors.  The code here originated
 * in ptrace.c and signal.c.
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
#include <linux/audit.h>
#include <linux/seccomp.h>
#include <linux/signal.h>
#include <linux/export.h>
#include <linux/context_tracking.h>
#include <linux/user-return-notifier.h>
#include <linux/uprobes.h>

#include <asm/desc.h>
#include <asm/traps.h>
#include <asm/vdso.h>
#include <asm/uaccess.h>
#include <asm/cpufeature.h>

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

static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
{
	unsigned long top_of_stack =
		(unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
	return (struct thread_info *)(top_of_stack - THREAD_SIZE);
}

#ifdef CONFIG_CONTEXT_TRACKING
/* Called on entry from user mode with IRQs off. */
__visible inline void enter_from_user_mode(void)
{
	CT_WARN_ON(ct_state() != CONTEXT_USER);
	user_exit_irqoff();
}
#else
static inline void enter_from_user_mode(void) {}
#endif

static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
{
#ifdef CONFIG_X86_64
	if (arch == AUDIT_ARCH_X86_64) {
		audit_syscall_entry(regs->orig_ax, regs->di,
				    regs->si, regs->dx, regs->r10);
	} else
#endif
	{
		audit_syscall_entry(regs->orig_ax, regs->bx,
				    regs->cx, regs->dx, regs->si);
	}
}

/*
 * Returns the syscall nr to run (which should match regs->orig_ax) or -1
 * to skip the syscall.
 */
static long syscall_trace_enter(struct pt_regs *regs)
{
	u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;

	struct thread_info *ti = pt_regs_to_thread_info(regs);
	unsigned long ret = 0;
	bool emulated = false;
	u32 work;

	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
		BUG_ON(regs != task_pt_regs(current));

	work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;

	if (unlikely(work & _TIF_SYSCALL_EMU))
		emulated = true;

	if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
	    tracehook_report_syscall_entry(regs))
		return -1L;

	if (emulated)
		return -1L;

#ifdef CONFIG_SECCOMP
	/*
	 * Do seccomp after ptrace, to catch any tracer changes.
	 */
	if (work & _TIF_SECCOMP) {
		struct seccomp_data sd;

		sd.arch = arch;
		sd.nr = regs->orig_ax;
		sd.instruction_pointer = regs->ip;
#ifdef CONFIG_X86_64
		if (arch == AUDIT_ARCH_X86_64) {
			sd.args[0] = regs->di;
			sd.args[1] = regs->si;
			sd.args[2] = regs->dx;
			sd.args[3] = regs->r10;
			sd.args[4] = regs->r8;
			sd.args[5] = regs->r9;
		} else
#endif
		{
			sd.args[0] = regs->bx;
			sd.args[1] = regs->cx;
			sd.args[2] = regs->dx;
			sd.args[3] = regs->si;
			sd.args[4] = regs->di;
			sd.args[5] = regs->bp;
		}

		ret = __secure_computing(&sd);
		if (ret == -1)
			return ret;
	}
#endif

	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
		trace_sys_enter(regs, regs->orig_ax);

	do_audit_syscall_entry(regs, arch);

	return ret ?: regs->orig_ax;
}

#define EXIT_TO_USERMODE_LOOP_FLAGS				\
	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)

static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
{
	/*
	 * In order to return to user mode, we need to have IRQs off with
	 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
	 * _TIF_UPROBE, or _TIF_NEED_RESCHED set.  Several of these flags
	 * can be set at any time on preemptable kernels if we have IRQs on,
	 * so we need to loop.  Disabling preemption wouldn't help: doing the
	 * work to clear some of the flags can sleep.
	 */
	while (true) {
		/* We have work to do. */
		local_irq_enable();

		if (cached_flags & _TIF_NEED_RESCHED)
			schedule();

		if (cached_flags & _TIF_UPROBE)
			uprobe_notify_resume(regs);

		/* deal with pending signal delivery */
		if (cached_flags & _TIF_SIGPENDING)
			do_signal(regs);

		if (cached_flags & _TIF_NOTIFY_RESUME) {
			clear_thread_flag(TIF_NOTIFY_RESUME);
			tracehook_notify_resume(regs);
			rseq_handle_notify_resume(regs);
		}

		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
			fire_user_return_notifiers();

		/* Disable IRQs and retry */
		local_irq_disable();

		cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);

		if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
			break;

	}
}

/* Called with IRQs disabled. */
__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
{
	struct thread_info *ti = pt_regs_to_thread_info(regs);
	u32 cached_flags;

	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
		local_irq_disable();

	lockdep_sys_exit();

	cached_flags = READ_ONCE(ti->flags);

	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
		exit_to_usermode_loop(regs, cached_flags);

#ifdef CONFIG_COMPAT
	/*
	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
	 * returning to user mode.  We need to clear it *after* signal
	 * handling, because syscall restart has a fixup for compat
	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
	 * selftest.
	 *
	 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
	 * special case only applies after poking regs and before the
	 * very next return to user mode.
	 */
	ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
#endif

	user_enter_irqoff();
}

#define SYSCALL_EXIT_WORK_FLAGS				\
	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |	\
	 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)

static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
{
	bool step;

	audit_syscall_exit(regs);

	if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
		trace_sys_exit(regs, regs->ax);

	/*
	 * If TIF_SYSCALL_EMU is set, we only get here because of
	 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
	 * We already reported this syscall instruction in
	 * syscall_trace_enter().
	 */
	step = unlikely(
		(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
		== _TIF_SINGLESTEP);
	if (step || cached_flags & _TIF_SYSCALL_TRACE)
		tracehook_report_syscall_exit(regs, step);
}

/*
 * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 * state such that we can immediately switch to user mode.
 */
__visible inline void syscall_return_slowpath(struct pt_regs *regs)
{
	struct thread_info *ti = pt_regs_to_thread_info(regs);
	u32 cached_flags = READ_ONCE(ti->flags);

	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);

	if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
	    WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
		local_irq_enable();

	/*
	 * First do one-time work.  If these work items are enabled, we
	 * want to run them exactly once per syscall exit with IRQs on.
	 */
	if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
		syscall_slow_exit_work(regs, cached_flags);

	local_irq_disable();
	prepare_exit_to_usermode(regs);
}

#ifdef CONFIG_X86_64
__visible void do_syscall_64(struct pt_regs *regs)
{
	struct thread_info *ti = pt_regs_to_thread_info(regs);
	unsigned long nr = regs->orig_ax;

	enter_from_user_mode();
	local_irq_enable();

	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
		nr = syscall_trace_enter(regs);

	/*
	 * NB: Native and x32 syscalls are dispatched from the same
	 * table.  The only functional difference is the x32 bit in
	 * regs->orig_ax, which changes the behavior of some syscalls.
	 */
	if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
		regs->ax = sys_call_table[nr & __SYSCALL_MASK](
			regs->di, regs->si, regs->dx,
			regs->r10, regs->r8, regs->r9);
	}

	syscall_return_slowpath(regs);
}
#endif

#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
/*
 * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
 * all entry and exit work and returns with IRQs off.  This function is
 * extremely hot in workloads that use it, and it's usually called from
 * do_fast_syscall_32, so forcibly inline it to improve performance.
 */
static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
{
	struct thread_info *ti = pt_regs_to_thread_info(regs);
	unsigned int nr = (unsigned int)regs->orig_ax;

#ifdef CONFIG_IA32_EMULATION
	ti->status |= TS_COMPAT;
#endif

	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
		/*
		 * Subtlety here: if ptrace pokes something larger than
		 * 2^32-1 into orig_ax, this truncates it.  This may or
		 * may not be necessary, but it matches the old asm
		 * behavior.
		 */
		nr = syscall_trace_enter(regs);
	}

	if (likely(nr < IA32_NR_syscalls)) {
		/*
		 * It's possible that a 32-bit syscall implementation
		 * takes a 64-bit parameter but nonetheless assumes that
		 * the high bits are zero.  Make sure we zero-extend all
		 * of the args.
		 */
		regs->ax = ia32_sys_call_table[nr](
			(unsigned int)regs->bx, (unsigned int)regs->cx,
			(unsigned int)regs->dx, (unsigned int)regs->si,
			(unsigned int)regs->di, (unsigned int)regs->bp);
	}

	syscall_return_slowpath(regs);
}

/* Handles int $0x80 */
__visible void do_int80_syscall_32(struct pt_regs *regs)
{
	enter_from_user_mode();
	local_irq_enable();
	do_syscall_32_irqs_on(regs);
}

/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible long do_fast_syscall_32(struct pt_regs *regs)
{
	/*
	 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
	 * convention.  Adjust regs so it looks like we entered using int80.
	 */

	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
		vdso_image_32.sym_int80_landing_pad;

	/*
	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
	 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
	 * Fix it up.
	 */
	regs->ip = landing_pad;

	enter_from_user_mode();

	local_irq_enable();

	/* Fetch EBP from where the vDSO stashed it. */
	if (
#ifdef CONFIG_X86_64
		/*
		 * Micro-optimization: the pointer we're following is explicitly
		 * 32 bits, so it can't be out of range.
		 */
		__get_user(*(u32 *)&regs->bp,
			    (u32 __user __force *)(unsigned long)(u32)regs->sp)
#else
		get_user(*(u32 *)&regs->bp,
			 (u32 __user __force *)(unsigned long)(u32)regs->sp)
#endif
		) {

		/* User code screwed up. */
		local_irq_disable();
		regs->ax = -EFAULT;
		prepare_exit_to_usermode(regs);
		return 0;	/* Keep it simple: use IRET. */
	}

	/* Now this is just like a normal syscall. */
	do_syscall_32_irqs_on(regs);

#ifdef CONFIG_X86_64
	/*
	 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
	 * SYSRETL is available on all 64-bit CPUs, so we don't need to
	 * bother with SYSEXIT.
	 *
	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
	 * because the ECX fixup above will ensure that this is essentially
	 * never the case.
	 */
	return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
		regs->ip == landing_pad &&
		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
#else
	/*
	 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
	 *
	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
	 * because the ECX fixup above will ensure that this is essentially
	 * never the case.
	 *
	 * We don't allow syscalls at all from VM86 mode, but we still
	 * need to check VM, because we might be returning from sys_vm86.
	 */
	return static_cpu_has(X86_FEATURE_SEP) &&
		regs->cs == __USER_CS && regs->ss == __USER_DS &&
		regs->ip == landing_pad &&
		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
#endif
}
#endif
Commit	Line	Data
1f484aa6 AL	1	/*
	2	* common.c - C code for kernel entry and exit
	3	* Copyright (c) 2015 Andrew Lutomirski
	4	* GPL v2
	5	*
	6	* Based on asm and ptrace code by many authors. The code here originated
	7	* in ptrace.c and signal.c.
	8	*/
	9
	10	#include <linux/kernel.h>
	11	#include <linux/sched.h>
	12	#include <linux/mm.h>
	13	#include <linux/smp.h>
	14	#include <linux/errno.h>
	15	#include <linux/ptrace.h>
	16	#include <linux/tracehook.h>
	17	#include <linux/audit.h>
	18	#include <linux/seccomp.h>
	19	#include <linux/signal.h>
	20	#include <linux/export.h>
	21	#include <linux/context_tracking.h>
	22	#include <linux/user-return-notifier.h>
	23	#include <linux/uprobes.h>
	24
	25	#include <asm/desc.h>
	26	#include <asm/traps.h>
710246df AL	27	#include <asm/vdso.h>
710246df AL	28	#include <asm/uaccess.h>
cd4d09ec	29	#include <asm/cpufeature.h>
1f484aa6 AL	30
	31	#define CREATE_TRACE_POINTS
	32	#include <trace/events/syscalls.h>
	33
dd636071 AL	34	static struct thread_info pt_regs_to_thread_info(struct pt_regs regs)
	35	{
	36	unsigned long top_of_stack =
	37	(unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
	38	return (struct thread_info *)(top_of_stack - THREAD_SIZE);
	39	}
	40
feed36cd AL	41	#ifdef CONFIG_CONTEXT_TRACKING
feed36cd AL	42	/* Called on entry from user mode with IRQs off. */
be8a18e2	43	__visible inline void enter_from_user_mode(void)
feed36cd AL	44	{
feed36cd AL	45	CT_WARN_ON(ct_state() != CONTEXT_USER);
2e9d1e15	46	user_exit_irqoff();
feed36cd	47	}
9999c8c0 AL	48	#else
9999c8c0 AL	49	static inline void enter_from_user_mode(void) {}
feed36cd AL	50	#endif
feed36cd AL	51
1f484aa6 AL	52	static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
	53	{
	54	#ifdef CONFIG_X86_64
	55	if (arch == AUDIT_ARCH_X86_64) {
	56	audit_syscall_entry(regs->orig_ax, regs->di,
	57	regs->si, regs->dx, regs->r10);
	58	} else
	59	#endif
	60	{
	61	audit_syscall_entry(regs->orig_ax, regs->bx,
	62	regs->cx, regs->dx, regs->si);
	63	}
	64	}
	65
	66	/*
c87a8517 AL	67	* Returns the syscall nr to run (which should match regs->orig_ax) or -1
c87a8517 AL	68	* to skip the syscall.
1f484aa6	69	*/
c87a8517	70	static long syscall_trace_enter(struct pt_regs *regs)
1f484aa6	71	{
c87a8517 AL	72	u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
c87a8517 AL	73
dd636071	74	struct thread_info *ti = pt_regs_to_thread_info(regs);
1f484aa6	75	unsigned long ret = 0;
93e35efb	76	bool emulated = false;
1f484aa6 AL	77	u32 work;
1f484aa6 AL	78
4aabd140 AL	79	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
4aabd140 AL	80	BUG_ON(regs != task_pt_regs(current));
1f484aa6	81
dd636071	82	work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
1f484aa6	83
93e35efb KC	84	if (unlikely(work & _TIF_SYSCALL_EMU))
	85	emulated = true;
	86
	87	if ((emulated \|\| (work & _TIF_SYSCALL_TRACE)) &&
	88	tracehook_report_syscall_entry(regs))
	89	return -1L;
	90
	91	if (emulated)
	92	return -1L;
	93
1f484aa6 AL	94	#ifdef CONFIG_SECCOMP
1f484aa6 AL	95	/*
93e35efb	96	* Do seccomp after ptrace, to catch any tracer changes.
1f484aa6 AL	97	*/
	98	if (work & _TIF_SECCOMP) {
	99	struct seccomp_data sd;
	100
	101	sd.arch = arch;
	102	sd.nr = regs->orig_ax;
	103	sd.instruction_pointer = regs->ip;
	104	#ifdef CONFIG_X86_64
	105	if (arch == AUDIT_ARCH_X86_64) {
	106	sd.args[0] = regs->di;
	107	sd.args[1] = regs->si;
	108	sd.args[2] = regs->dx;
	109	sd.args[3] = regs->r10;
	110	sd.args[4] = regs->r8;
	111	sd.args[5] = regs->r9;
	112	} else
	113	#endif
	114	{
	115	sd.args[0] = regs->bx;
	116	sd.args[1] = regs->cx;
	117	sd.args[2] = regs->dx;
	118	sd.args[3] = regs->si;
	119	sd.args[4] = regs->di;
	120	sd.args[5] = regs->bp;
	121	}
	122
c87a8517 AL	123	ret = __secure_computing(&sd);
	124	if (ret == -1)
	125	return ret;
1f484aa6 AL	126	}
	127	#endif
	128
1f484aa6 AL	129	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
	130	trace_sys_enter(regs, regs->orig_ax);
	131
	132	do_audit_syscall_entry(regs, arch);
	133
	134	return ret ?: regs->orig_ax;
	135	}
	136
39b48e57 AL	137	#define EXIT_TO_USERMODE_LOOP_FLAGS \
	138	(_TIF_SIGPENDING \| _TIF_NOTIFY_RESUME \| _TIF_UPROBE \| \
	139	_TIF_NEED_RESCHED \| _TIF_USER_RETURN_NOTIFY)
72f92478	140
39b48e57 AL	141	static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
39b48e57 AL	142	{
c5c46f59 AL	143	/*
	144	* In order to return to user mode, we need to have IRQs off with
	145	* none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
	146	* _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags
	147	* can be set at any time on preemptable kernels if we have IRQs on,
	148	* so we need to loop. Disabling preemption wouldn't help: doing the
	149	* work to clear some of the flags can sleep.
	150	*/
	151	while (true) {
c5c46f59 AL	152	/* We have work to do. */
	153	local_irq_enable();
	154
	155	if (cached_flags & _TIF_NEED_RESCHED)
	156	schedule();
	157
	158	if (cached_flags & _TIF_UPROBE)
	159	uprobe_notify_resume(regs);
	160
	161	/* deal with pending signal delivery */
	162	if (cached_flags & _TIF_SIGPENDING)
	163	do_signal(regs);
	164
	165	if (cached_flags & _TIF_NOTIFY_RESUME) {
	166	clear_thread_flag(TIF_NOTIFY_RESUME);
	167	tracehook_notify_resume(regs);
5bd6bfc2	168	rseq_handle_notify_resume(regs);
c5c46f59 AL	169	}
	170
	171	if (cached_flags & _TIF_USER_RETURN_NOTIFY)
	172	fire_user_return_notifiers();
	173
	174	/* Disable IRQs and retry */
	175	local_irq_disable();
39b48e57 AL	176
	177	cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
	178
	179	if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
	180	break;
	181
c5c46f59	182	}
39b48e57 AL	183	}
	184
	185	/* Called with IRQs disabled. */
	186	__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
	187	{
4e79e182	188	struct thread_info *ti = pt_regs_to_thread_info(regs);
39b48e57 AL	189	u32 cached_flags;
	190
	191	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
	192	local_irq_disable();
	193
	194	lockdep_sys_exit();
	195
4e79e182	196	cached_flags = READ_ONCE(ti->flags);
39b48e57 AL	197
	198	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
	199	exit_to_usermode_loop(regs, cached_flags);
c5c46f59	200
4e79e182 AL	201	#ifdef CONFIG_COMPAT
	202	/*
	203	* Compat syscalls set TS_COMPAT. Make sure we clear it before
	204	* returning to user mode. We need to clear it after signal
	205	* handling, because syscall restart has a fixup for compat
	206	* syscalls. The fixup is exercised by the ptrace_syscall_32
	207	* selftest.
609c19a3 AL	208	*
	209	* We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
	210	* special case only applies after poking regs and before the
	211	* very next return to user mode.
4e79e182	212	*/
609c19a3	213	ti->status &= ~(TS_COMPAT\|TS_I386_REGS_POKED);
4e79e182 AL	214	#endif
4e79e182 AL	215
2e9d1e15	216	user_enter_irqoff();
c5c46f59 AL	217	}
c5c46f59 AL	218
f5e6a975 AL	219	#define SYSCALL_EXIT_WORK_FLAGS \
	220	(_TIF_SYSCALL_TRACE \| _TIF_SYSCALL_AUDIT \| \
	221	_TIF_SINGLESTEP \| _TIF_SYSCALL_TRACEPOINT)
	222
	223	static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
	224	{
	225	bool step;
	226
	227	audit_syscall_exit(regs);
	228
	229	if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
	230	trace_sys_exit(regs, regs->ax);
	231
	232	/*
	233	* If TIF_SYSCALL_EMU is set, we only get here because of
	234	* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
	235	* We already reported this syscall instruction in
	236	* syscall_trace_enter().
	237	*/
	238	step = unlikely(
	239	(cached_flags & (_TIF_SINGLESTEP \| _TIF_SYSCALL_EMU))
	240	== _TIF_SINGLESTEP);
	241	if (step \|\| cached_flags & _TIF_SYSCALL_TRACE)
	242	tracehook_report_syscall_exit(regs, step);
	243	}
	244
c5c46f59 AL	245	/*
	246	* Called with IRQs on and fully valid regs. Returns with IRQs off in a
	247	* state such that we can immediately switch to user mode.
	248	*/
f5e6a975	249	__visible inline void syscall_return_slowpath(struct pt_regs *regs)
c5c46f59 AL	250	{
	251	struct thread_info *ti = pt_regs_to_thread_info(regs);
	252	u32 cached_flags = READ_ONCE(ti->flags);
c5c46f59 AL	253
	254	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
	255
460d1245 AL	256	if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
460d1245 AL	257	WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
c5c46f59 AL	258	local_irq_enable();
	259
	260	/*
	261	* First do one-time work. If these work items are enabled, we
	262	* want to run them exactly once per syscall exit with IRQs on.
	263	*/
f5e6a975 AL	264	if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
f5e6a975 AL	265	syscall_slow_exit_work(regs, cached_flags);
c5c46f59	266
c5c46f59 AL	267	local_irq_disable();
	268	prepare_exit_to_usermode(regs);
	269	}
bd2d3a3b	270
1e423bff AL	271	#ifdef CONFIG_X86_64
	272	__visible void do_syscall_64(struct pt_regs *regs)
	273	{
	274	struct thread_info *ti = pt_regs_to_thread_info(regs);
	275	unsigned long nr = regs->orig_ax;
	276
9999c8c0	277	enter_from_user_mode();
1e423bff AL	278	local_irq_enable();
	279
	280	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
	281	nr = syscall_trace_enter(regs);
	282
	283	/*
	284	* NB: Native and x32 syscalls are dispatched from the same
	285	* table. The only functional difference is the x32 bit in
	286	* regs->orig_ax, which changes the behavior of some syscalls.
	287	*/
	288	if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
	289	regs->ax = sys_call_table[nr & __SYSCALL_MASK](
	290	regs->di, regs->si, regs->dx,
	291	regs->r10, regs->r8, regs->r9);
	292	}
	293
	294	syscall_return_slowpath(regs);
	295	}
	296	#endif
	297
bd2d3a3b AL	298	#if defined(CONFIG_X86_32) \|\| defined(CONFIG_IA32_EMULATION)
bd2d3a3b AL	299	/*
9999c8c0 AL	300	* Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
	301	* all entry and exit work and returns with IRQs off. This function is
	302	* extremely hot in workloads that use it, and it's usually called from
33c52129	303	* do_fast_syscall_32, so forcibly inline it to improve performance.
bd2d3a3b	304	*/
a798f091	305	static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
bd2d3a3b AL	306	{
	307	struct thread_info *ti = pt_regs_to_thread_info(regs);
	308	unsigned int nr = (unsigned int)regs->orig_ax;
	309
	310	#ifdef CONFIG_IA32_EMULATION
	311	ti->status \|= TS_COMPAT;
	312	#endif
	313
bd2d3a3b AL	314	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
	315	/*
	316	* Subtlety here: if ptrace pokes something larger than
	317	* 2^32-1 into orig_ax, this truncates it. This may or
	318	* may not be necessary, but it matches the old asm
	319	* behavior.
	320	*/
	321	nr = syscall_trace_enter(regs);
	322	}
	323
33c52129	324	if (likely(nr < IA32_NR_syscalls)) {
bd2d3a3b AL	325	/*
	326	* It's possible that a 32-bit syscall implementation
	327	* takes a 64-bit parameter but nonetheless assumes that
	328	* the high bits are zero. Make sure we zero-extend all
	329	* of the args.
	330	*/
	331	regs->ax = ia32_sys_call_table[nr](
	332	(unsigned int)regs->bx, (unsigned int)regs->cx,
	333	(unsigned int)regs->dx, (unsigned int)regs->si,
	334	(unsigned int)regs->di, (unsigned int)regs->bp);
	335	}
	336
	337	syscall_return_slowpath(regs);
	338	}
710246df	339
a798f091 AL	340	/* Handles int $0x80 */
a798f091 AL	341	__visible void do_int80_syscall_32(struct pt_regs *regs)
8b13c255	342	{
9999c8c0	343	enter_from_user_mode();
8b13c255 AL	344	local_irq_enable();
	345	do_syscall_32_irqs_on(regs);
	346	}
	347
5f310f73	348	/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
7841b408	349	__visible long do_fast_syscall_32(struct pt_regs *regs)
710246df AL	350	{
	351	/*
	352	* Called using the internal vDSO SYSENTER/SYSCALL32 calling
	353	* convention. Adjust regs so it looks like we entered using int80.
	354	*/
	355
	356	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
	357	vdso_image_32.sym_int80_landing_pad;
	358
	359	/*
	360	* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
	361	* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
	362	* Fix it up.
	363	*/
	364	regs->ip = landing_pad;
	365
9999c8c0 AL	366	enter_from_user_mode();
9999c8c0 AL	367
710246df	368	local_irq_enable();
9999c8c0 AL	369
9999c8c0 AL	370	/* Fetch EBP from where the vDSO stashed it. */
c68ca678 AL	371	if (
	372	#ifdef CONFIG_X86_64
	373	/*
	374	* Micro-optimization: the pointer we're following is explicitly
	375	* 32 bits, so it can't be out of range.
	376	*/
30bfa7b3	377	__get_user((u32 )&regs->bp,
c68ca678 AL	378	(u32 __user __force *)(unsigned long)(u32)regs->sp)
c68ca678 AL	379	#else
30bfa7b3	380	get_user((u32 )&regs->bp,
c68ca678 AL	381	(u32 __user __force *)(unsigned long)(u32)regs->sp)
	382	#endif
	383	) {
	384
710246df AL	385	/* User code screwed up. */
	386	local_irq_disable();
	387	regs->ax = -EFAULT;
710246df	388	prepare_exit_to_usermode(regs);
7841b408	389	return 0; /* Keep it simple: use IRET. */
710246df	390	}
710246df AL	391
710246df AL	392	/* Now this is just like a normal syscall. */
8b13c255	393	do_syscall_32_irqs_on(regs);
7841b408 AL	394
	395	#ifdef CONFIG_X86_64
	396	/*
	397	* Opportunistic SYSRETL: if possible, try to return using SYSRETL.
	398	* SYSRETL is available on all 64-bit CPUs, so we don't need to
	399	* bother with SYSEXIT.
	400	*
	401	* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
	402	* because the ECX fixup above will ensure that this is essentially
	403	* never the case.
	404	*/
	405	return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
	406	regs->ip == landing_pad &&
	407	(regs->flags & (X86_EFLAGS_RF \| X86_EFLAGS_TF)) == 0;
	408	#else
5f310f73 AL	409	/*
	410	* Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
	411	*
	412	* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
	413	* because the ECX fixup above will ensure that this is essentially
	414	* never the case.
	415	*
	416	* We don't allow syscalls at all from VM86 mode, but we still
	417	* need to check VM, because we might be returning from sys_vm86.
	418	*/
	419	return static_cpu_has(X86_FEATURE_SEP) &&
	420	regs->cs == __USER_CS && regs->ss == __USER_DS &&
	421	regs->ip == landing_pad &&
	422	(regs->flags & (X86_EFLAGS_RF \| X86_EFLAGS_TF \| X86_EFLAGS_VM)) == 0;
7841b408	423	#endif
710246df	424	}
bd2d3a3b	425	#endif