arch/x86/entry/common.c - kernel/msm-4.9 - Gitiles

 /*
  * 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>

 #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 void enter_from_user_mode(void)
 {
 	CT_WARN_ON(ct_state() != CONTEXT_USER);
 	user_exit();
 }
 #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);
 	}
 }

 /*
  * We can return 0 to resume the syscall or anything else to go to phase
  * 2.  If we resume the syscall, we need to put something appropriate in
  * regs->orig_ax.
  *
  * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
  * are fully functional.
  *
  * For phase 2's benefit, our return value is:
  * 0:			resume the syscall
  * 1:			go to phase 2; no seccomp phase 2 needed
  * anything else:	go to phase 2; pass return value to seccomp
  */
 unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 {
 	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	unsigned long ret = 0;
 	u32 work;

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

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

 #ifdef CONFIG_CONTEXT_TRACKING
 	/*
 	 * If TIF_NOHZ is set, we are required to call user_exit() before
 	 * doing anything that could touch RCU.
 	 */
 	if (work & _TIF_NOHZ) {
 		enter_from_user_mode();
 		work &= ~_TIF_NOHZ;
 	}
 #endif

 #ifdef CONFIG_SECCOMP
 	/*
 	 * Do seccomp first -- it should minimize exposure of other
 	 * code, and keeping seccomp fast is probably more valuable
 	 * than the rest of this.
 	 */
 	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;
 		}

 		BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
 		BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);

 		ret = seccomp_phase1(&sd);
 		if (ret == SECCOMP_PHASE1_SKIP) {
 			regs->orig_ax = -1;
 			ret = 0;
 		} else if (ret != SECCOMP_PHASE1_OK) {
 			return ret;  /* Go directly to phase 2 */
 		}

 		work &= ~_TIF_SECCOMP;
 	}
 #endif

 	/* Do our best to finish without phase 2. */
 	if (work == 0)
 		return ret;  /* seccomp and/or nohz only (ret == 0 here) */

 #ifdef CONFIG_AUDITSYSCALL
 	if (work == _TIF_SYSCALL_AUDIT) {
 		/*
 		 * If there is no more work to be done except auditing,
 		 * then audit in phase 1.  Phase 2 always audits, so, if
 		 * we audit here, then we can't go on to phase 2.
 		 */
 		do_audit_syscall_entry(regs, arch);
 		return 0;
 	}
 #endif

 	return 1;  /* Something is enabled that we can't handle in phase 1 */
 }

 /* Returns the syscall nr to run (which should match regs->orig_ax). */
 long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
 				unsigned long phase1_result)
 {
 	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	long ret = 0;
 	u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;

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

 	/*
 	 * If we stepped into a sysenter/syscall insn, it trapped in
 	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
 	 * If user-mode had set TF itself, then it's still clear from
 	 * do_debug() and we need to set it again to restore the user
 	 * state.  If we entered on the slow path, TF was already set.
 	 */
 	if (work & _TIF_SINGLESTEP)
 		regs->flags |= X86_EFLAGS_TF;

 #ifdef CONFIG_SECCOMP
 	/*
 	 * Call seccomp_phase2 before running the other hooks so that
 	 * they can see any changes made by a seccomp tracer.
 	 */
 	if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
 		/* seccomp failures shouldn't expose any additional code. */
 		return -1;
 	}
 #endif

 	if (unlikely(work & _TIF_SYSCALL_EMU))
 		ret = -1L;

 	if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
 	    tracehook_report_syscall_entry(regs))
 		ret = -1L;

 	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;
 }

 long syscall_trace_enter(struct pt_regs *regs)
 {
 	u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
 	unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);

 	if (phase1_result == 0)
 		return regs->orig_ax;
 	else
 		return syscall_trace_enter_phase2(regs, arch, phase1_result);
 }

 #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);
 		}

 		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)
 {
 	u32 cached_flags;

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

 	lockdep_sys_exit();

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

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

 	user_enter();
 }

 /*
  * 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 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);
 	bool step;

 	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 (cached_flags & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |
 			    _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)) {
 		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);
 	}

 #ifdef CONFIG_COMPAT
 	/*
 	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 	 * returning to user mode.
 	 */
 	ti->status &= ~TS_COMPAT;
 #endif

 	local_irq_disable();
 	prepare_exit_to_usermode(regs);
 }

 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 /*
  * Does a 32-bit syscall.  Called with IRQs on and 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)
 {
 	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;

 	/*
 	 * Fetch ECX from where the vDSO stashed it.
 	 *
 	 * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
 	 */
 	local_irq_enable();
 	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->cx,
 			    (u32 __user __force *)(unsigned long)(u32)regs->sp)
 #else
 		get_user(*(u32 *)&regs->cx,
 			 (u32 __user __force *)(unsigned long)(u32)regs->sp)
 #endif
 		) {

 		/* User code screwed up. */
 		local_irq_disable();
 		regs->ax = -EFAULT;
 #ifdef CONFIG_CONTEXT_TRACKING
 		enter_from_user_mode();
 #endif
 		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
	/*
	* 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>

	#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 void enter_from_user_mode(void)
	{
	CT_WARN_ON(ct_state() != CONTEXT_USER);
	user_exit();
	}
	#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);
	}
	}

	/*
	* We can return 0 to resume the syscall or anything else to go to phase
	* 2. If we resume the syscall, we need to put something appropriate in
	* regs->orig_ax.
	*
	* NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
	* are fully functional.
	*
	* For phase 2's benefit, our return value is:
	* 0: resume the syscall
	* 1: go to phase 2; no seccomp phase 2 needed
	* anything else: go to phase 2; pass return value to seccomp
	*/
	unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
	{
	struct thread_info *ti = pt_regs_to_thread_info(regs);
	unsigned long ret = 0;
	u32 work;

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

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

	#ifdef CONFIG_CONTEXT_TRACKING
	/*
	* If TIF_NOHZ is set, we are required to call user_exit() before
	* doing anything that could touch RCU.
	*/
	if (work & _TIF_NOHZ) {
	enter_from_user_mode();
	work &= ~_TIF_NOHZ;
	}
	#endif

	#ifdef CONFIG_SECCOMP
	/*
	* Do seccomp first -- it should minimize exposure of other
	* code, and keeping seccomp fast is probably more valuable
	* than the rest of this.
	*/
	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;
	}

	BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
	BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);

	ret = seccomp_phase1(&sd);
	if (ret == SECCOMP_PHASE1_SKIP) {
	regs->orig_ax = -1;
	ret = 0;
	} else if (ret != SECCOMP_PHASE1_OK) {
	return ret; /* Go directly to phase 2 */
	}

	work &= ~_TIF_SECCOMP;
	}
	#endif

	/* Do our best to finish without phase 2. */
	if (work == 0)
	return ret; /* seccomp and/or nohz only (ret == 0 here) */

	#ifdef CONFIG_AUDITSYSCALL
	if (work == _TIF_SYSCALL_AUDIT) {
	/*
	* If there is no more work to be done except auditing,
	* then audit in phase 1. Phase 2 always audits, so, if
	* we audit here, then we can't go on to phase 2.
	*/
	do_audit_syscall_entry(regs, arch);
	return 0;
	}
	#endif

	return 1; /* Something is enabled that we can't handle in phase 1 */
	}

	/* Returns the syscall nr to run (which should match regs->orig_ax). */
	long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
	unsigned long phase1_result)
	{
	struct thread_info *ti = pt_regs_to_thread_info(regs);
	long ret = 0;
	u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;

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

	/*
	* If we stepped into a sysenter/syscall insn, it trapped in
	* kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
	* If user-mode had set TF itself, then it's still clear from
	* do_debug() and we need to set it again to restore the user
	* state. If we entered on the slow path, TF was already set.
	*/
	if (work & _TIF_SINGLESTEP)
	regs->flags \|= X86_EFLAGS_TF;

	#ifdef CONFIG_SECCOMP
	/*
	* Call seccomp_phase2 before running the other hooks so that
	* they can see any changes made by a seccomp tracer.
	*/
	if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
	/* seccomp failures shouldn't expose any additional code. */
	return -1;
	}
	#endif

	if (unlikely(work & _TIF_SYSCALL_EMU))
	ret = -1L;

	if ((ret \|\| test_thread_flag(TIF_SYSCALL_TRACE)) &&
	tracehook_report_syscall_entry(regs))
	ret = -1L;

	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;
	}

	long syscall_trace_enter(struct pt_regs *regs)
	{
	u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
	unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);

	if (phase1_result == 0)
	return regs->orig_ax;
	else
	return syscall_trace_enter_phase2(regs, arch, phase1_result);
	}

	#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);
	}

	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)
	{
	u32 cached_flags;

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

	lockdep_sys_exit();

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

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

	user_enter();
	}

	/*
	* 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 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);
	bool step;

	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 (cached_flags & (_TIF_SYSCALL_TRACE \| _TIF_SYSCALL_AUDIT \|
	_TIF_SINGLESTEP \| _TIF_SYSCALL_TRACEPOINT)) {
	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);
	}

	#ifdef CONFIG_COMPAT
	/*
	* Compat syscalls set TS_COMPAT. Make sure we clear it before
	* returning to user mode.
	*/
	ti->status &= ~TS_COMPAT;
	#endif

	local_irq_disable();
	prepare_exit_to_usermode(regs);
	}

	#if defined(CONFIG_X86_32) \|\| defined(CONFIG_IA32_EMULATION)
	/*
	* Does a 32-bit syscall. Called with IRQs on and 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)
	{
	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;

	/*
	* Fetch ECX from where the vDSO stashed it.
	*
	* WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
	*/
	local_irq_enable();
	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->cx,
	(u32 __user __force *)(unsigned long)(u32)regs->sp)
	#else
	get_user((u32 )&regs->cx,
	(u32 __user __force *)(unsigned long)(u32)regs->sp)
	#endif
	) {

	/* User code screwed up. */
	local_irq_disable();
	regs->ax = -EFAULT;
	#ifdef CONFIG_CONTEXT_TRACKING
	enter_from_user_mode();
	#endif
	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