[PATCH 6/7] implement utrace-ptrace

[Oleg Nesterov <oleg@redhat.com>]

The patch adds the new file, kernel/ptrace-utrace.c, which contains
the new implementation of ptrace over utrace.

This file is not compiled until we have CONFIG_UTRACE option, will be
added by the next "utrace core" patch.

It's supposed to be an invisible implementation change, nothing should
change to userland when CONFIG_UTRACE is enabled.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

 include/linux/ptrace.h |    2 
 kernel/Makefile        |    1 
 kernel/ptrace.c        |    2 
 kernel/ptrace-utrace.c | 1080 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 1084 insertions(+), 1 deletion(-)

--- V1/include/linux/ptrace.h~6_UTRACE_PTRACE	2009-12-18 00:53:58.000000000 +0100
+++ V1/include/linux/ptrace.h	2009-12-18 01:04:56.000000000 +0100
@@ -79,7 +79,7 @@
 #include <linux/compiler.h>		/* For unlikely.  */
 #include <linux/sched.h>		/* For struct task_struct.  */
 
-
+extern void ptrace_notify_stop(struct task_struct *tracee);
 extern long arch_ptrace(struct task_struct *child, long request, long addr, long data);
 extern int ptrace_traceme(void);
 extern int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len);
--- V1/kernel/Makefile~6_UTRACE_PTRACE	2009-12-18 00:20:50.000000000 +0100
+++ V1/kernel/Makefile	2009-12-18 01:57:41.000000000 +0100
@@ -69,6 +69,7 @@ obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
 obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
 obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
+obj-$(CONFIG_UTRACE) += ptrace-utrace.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o audit_watch.o
 obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
 obj-$(CONFIG_GCOV_KERNEL) += gcov/
--- V1/kernel/ptrace.c~6_UTRACE_PTRACE	2009-12-18 01:00:26.000000000 +0100
+++ V1/kernel/ptrace.c	2009-12-18 01:04:56.000000000 +0100
@@ -302,6 +302,7 @@ asmlinkage long compat_sys_ptrace(compat
 }
 #endif	/* CONFIG_COMPAT */
 
+#ifndef CONFIG_UTRACE
 /*
  * ptrace a task: make the debugger its new parent and
  * move it to the ptrace list.
@@ -762,3 +763,4 @@ int compat_ptrace_request(struct task_st
 	return ret;
 }
 #endif	/* CONFIG_COMPAT */
+#endif	/* CONFIG_UTRACE */
--- /dev/null	2009-12-15 18:13:27.615265787 +0100
+++ V1/kernel/ptrace-utrace.c	2009-12-18 01:09:36.000000000 +0100
@@ -0,0 +1,1080 @@
+/*
+ * linux/kernel/ptrace.c
+ *
+ * (C) Copyright 1999 Linus Torvalds
+ *
+ * Common interfaces for "ptrace()" which we do not want
+ * to continually duplicate across every architecture.
+ */
+
+#include <linux/capability.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>
+#include <linux/smp_lock.h>
+#include <linux/ptrace.h>
+#include <linux/utrace.h>
+#include <linux/security.h>
+#include <linux/signal.h>
+#include <linux/audit.h>
+#include <linux/pid_namespace.h>
+#include <linux/syscalls.h>
+#include <linux/uaccess.h>
+
+/*
+ * ptrace a task: make the debugger its new parent and
+ * move it to the ptrace list.
+ *
+ * Must be called with the tasklist lock write-held.
+ */
+void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
+{
+	BUG_ON(!list_empty(&child->ptrace_entry));
+	list_add(&child->ptrace_entry, &new_parent->ptraced);
+	child->parent = new_parent;
+}
+
+/*
+ * unptrace a task: move it back to its original parent and
+ * remove it from the ptrace list.
+ *
+ * Must be called with the tasklist lock write-held.
+ */
+void __ptrace_unlink(struct task_struct *child)
+{
+	BUG_ON(!child->ptrace);
+
+	child->ptrace = 0;
+	child->parent = child->real_parent;
+	list_del_init(&child->ptrace_entry);
+
+	arch_ptrace_untrace(child);
+}
+
+struct ptrace_context {
+	int				options;
+
+	int				signr;
+	siginfo_t			*siginfo;
+
+	int				stop_code;
+	unsigned long			eventmsg;
+
+	enum utrace_resume_action	resume;
+};
+
+#define PT_UTRACED			0x00001000
+
+#define PTRACE_O_SYSEMU			0x100
+
+#define PTRACE_EVENT_SYSCALL		(1 << 16)
+#define PTRACE_EVENT_SIGTRAP		(2 << 16)
+#define PTRACE_EVENT_SIGNAL		(3 << 16)
+/* events visible to user-space */
+#define PTRACE_EVENT_MASK		0xFFFF
+
+static inline bool ptrace_event_pending(struct ptrace_context *ctx)
+{
+	return ctx->stop_code != 0;
+}
+
+static inline int get_stop_event(struct ptrace_context *ctx)
+{
+	return ctx->stop_code >> 8;
+}
+
+static inline void set_stop_code(struct ptrace_context *ctx, int event)
+{
+	ctx->stop_code = (event << 8) | SIGTRAP;
+}
+
+static inline struct ptrace_context *
+ptrace_context(struct utrace_engine *engine)
+{
+	return engine->data;
+}
+
+static const struct utrace_engine_ops ptrace_utrace_ops; /* forward decl */
+
+static struct utrace_engine *ptrace_lookup_engine(struct task_struct *tracee)
+{
+	return utrace_attach_task(tracee, UTRACE_ATTACH_MATCH_OPS,
+					&ptrace_utrace_ops, NULL);
+}
+
+static struct utrace_engine *
+ptrace_reuse_engine(struct task_struct *tracee)
+{
+	struct utrace_engine *engine;
+	struct ptrace_context *ctx;
+	int err = -EPERM;
+
+	engine = ptrace_lookup_engine(tracee);
+	if (IS_ERR(engine))
+		return engine;
+
+	ctx = ptrace_context(engine);
+	if (unlikely(ctx->resume == UTRACE_DETACH)) {
+		/*
+		 * Try to reuse this self-detaching engine.
+		 * The only caller which can hit this case is ptrace_attach(),
+		 * it holds ->cred_guard_mutex.
+		 */
+		ctx->options = 0;
+		ctx->eventmsg = 0;
+
+		/* make sure we don't get unwanted reports */
+		err = utrace_set_events(tracee, engine, UTRACE_EVENT(QUIESCE));
+		if (!err || err == -EINPROGRESS) {
+			ctx->resume = UTRACE_RESUME;
+			/* synchronize with ptrace_report_signal() */
+			err = utrace_barrier(tracee, engine);
+		}
+		WARN_ON(!err != (engine->ops == &ptrace_utrace_ops));
+
+		if (!err)
+			return engine;
+	}
+
+	utrace_engine_put(engine);
+	return ERR_PTR(err);
+}
+
+static struct utrace_engine *
+ptrace_attach_engine(struct task_struct *tracee)
+{
+	struct utrace_engine *engine;
+	struct ptrace_context *ctx;
+
+	if (unlikely(task_utrace_flags(tracee))) {
+		engine = ptrace_reuse_engine(tracee);
+		if (!IS_ERR(engine) || IS_ERR(engine) == -EPERM)
+			return engine;
+	}
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (unlikely(!ctx))
+		return ERR_PTR(-ENOMEM);
+
+	ctx->resume = UTRACE_RESUME;
+
+	engine = utrace_attach_task(tracee, UTRACE_ATTACH_CREATE |
+						UTRACE_ATTACH_EXCLUSIVE |
+						UTRACE_ATTACH_MATCH_OPS,
+						&ptrace_utrace_ops, ctx);
+	if (unlikely(IS_ERR(engine))) {
+		if (engine != ERR_PTR(-ESRCH) &&
+		    engine != ERR_PTR(-ERESTARTNOINTR))
+			engine = ERR_PTR(-EPERM);
+		kfree(ctx);
+	}
+
+	return engine;
+}
+
+static inline int ptrace_set_events(struct task_struct *target,
+					struct utrace_engine *engine,
+					unsigned long options)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+	/*
+	 * We need QUIESCE for resume handling, CLONE to check
+	 * for CLONE_PTRACE, other events are always reported.
+	 */
+	unsigned long events = UTRACE_EVENT(QUIESCE) | UTRACE_EVENT(CLONE) |
+			       UTRACE_EVENT(EXEC) | UTRACE_EVENT_SIGNAL_ALL;
+
+	ctx->options = options;
+	if (options & PTRACE_O_TRACEEXIT)
+		events |= UTRACE_EVENT(EXIT);
+
+	return utrace_set_events(target, engine, events);
+}
+
+/*
+ * Attach a utrace engine for ptrace and set up its event mask.
+ * Returns error code or 0 on success.
+ */
+static int ptrace_attach_task(struct task_struct *tracee, int options)
+{
+	struct utrace_engine *engine;
+	int err;
+
+	engine = ptrace_attach_engine(tracee);
+	if (IS_ERR(engine))
+		return PTR_ERR(engine);
+	/*
+	 * It can fail only if the tracee is dead, the caller
+	 * must notice this before setting PT_UTRACED.
+	 */
+	err = ptrace_set_events(tracee, engine, options);
+	WARN_ON(err && !tracee->exit_state);
+	utrace_engine_put(engine);
+	return 0;
+}
+
+static int ptrace_wake_up(struct task_struct *tracee,
+				struct utrace_engine *engine,
+				enum utrace_resume_action action,
+				bool force_wakeup)
+{
+	if (force_wakeup) {
+		unsigned long flags;
+		/*
+		 * Preserve the compatibility bug. Historically ptrace
+		 * wakes up the tracee even if it should not. Clear
+		 * SIGNAL_STOP_STOPPED for utrace_wakeup().
+		 */
+		if (lock_task_sighand(tracee, &flags)) {
+			tracee->signal->flags &= ~SIGNAL_STOP_STOPPED;
+			unlock_task_sighand(tracee, &flags);
+		}
+	}
+
+	if (action != UTRACE_REPORT)
+		ptrace_context(engine)->stop_code = 0;
+
+	return utrace_control(tracee, engine, action);
+}
+
+static void ptrace_detach_task(struct task_struct *tracee, int sig)
+{
+	/*
+	 * If true, the caller is PTRACE_DETACH, otherwise
+	 * the tracer detaches implicitly during exit.
+	 */
+	bool voluntary = (sig >= 0);
+	struct utrace_engine *engine = ptrace_lookup_engine(tracee);
+	enum utrace_resume_action action = UTRACE_DETACH;
+
+	if (unlikely(IS_ERR(engine)))
+		return;
+
+	if (sig) {
+		struct ptrace_context *ctx = ptrace_context(engine);
+
+		switch (get_stop_event(ctx)) {
+		case PTRACE_EVENT_SYSCALL:
+			if (voluntary)
+				send_sig_info(sig, SEND_SIG_PRIV, tracee);
+			break;
+
+		case PTRACE_EVENT_SIGNAL:
+			if (voluntary)
+				ctx->signr = sig;
+			ctx->resume = UTRACE_DETACH;
+			action = UTRACE_RESUME;
+			break;
+		}
+	}
+
+	ptrace_wake_up(tracee, engine, action, voluntary);
+	utrace_engine_put(engine);
+}
+
+static void ptrace_abort_attach(struct task_struct *tracee)
+{
+	ptrace_detach_task(tracee, 0);
+}
+
+static u32 ptrace_report_exit(u32 action, struct utrace_engine *engine,
+			      long orig_code, long *code)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+
+	WARN_ON(ptrace_event_pending(ctx) &&
+		!signal_group_exit(current->signal));
+
+	set_stop_code(ctx, PTRACE_EVENT_EXIT);
+	ctx->eventmsg = *code;
+
+	return UTRACE_STOP;
+}
+
+static void ptrace_clone_attach(struct task_struct *child,
+				int options)
+{
+	struct task_struct *parent = current;
+	struct task_struct *tracer;
+	bool abort = true;
+
+	if (unlikely(ptrace_attach_task(child, options))) {
+		WARN_ON(1);
+		return;
+	}
+
+	write_lock_irq(&tasklist_lock);
+	tracer = parent->parent;
+	if (!(tracer->flags & PF_EXITING) && parent->ptrace) {
+		child->ptrace = parent->ptrace;
+		__ptrace_link(child, tracer);
+		abort = false;
+	}
+	write_unlock_irq(&tasklist_lock);
+	if (unlikely(abort)) {
+		ptrace_abort_attach(child);
+		return;
+	}
+
+	sigaddset(&child->pending.signal, SIGSTOP);
+	set_tsk_thread_flag(child, TIF_SIGPENDING);
+}
+
+static u32 ptrace_report_clone(u32 action, struct utrace_engine *engine,
+			       unsigned long clone_flags,
+			       struct task_struct *child)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+	int event = 0;
+
+	WARN_ON(ptrace_event_pending(ctx));
+
+	if (clone_flags & CLONE_UNTRACED) {
+		/* no events reported */
+	} else if (clone_flags & CLONE_VFORK) {
+		if (ctx->options & PTRACE_O_TRACEVFORK)
+			event = PTRACE_EVENT_VFORK;
+		else if (ctx->options & PTRACE_O_TRACEVFORKDONE)
+			event = PTRACE_EVENT_VFORK_DONE;
+	} else if ((clone_flags & CSIGNAL) != SIGCHLD) {
+		if (ctx->options & PTRACE_O_TRACECLONE)
+			event = PTRACE_EVENT_CLONE;
+	} else if (ctx->options & PTRACE_O_TRACEFORK) {
+		event = PTRACE_EVENT_FORK;
+	}
+	/*
+	 * Any of these reports implies auto-attaching the new child.
+	 * So does CLONE_PTRACE, even with no event to report.
+	 */
+	if ((event && event != PTRACE_EVENT_VFORK_DONE) ||
+				(clone_flags & CLONE_PTRACE))
+		ptrace_clone_attach(child, ctx->options);
+
+	if (!event)
+		return UTRACE_RESUME;
+
+	set_stop_code(ctx, event);
+	ctx->eventmsg = child->pid;
+	/*
+	 * We shouldn't stop now, inside the do_fork() path.
+	 * We will stop later, before return to user-mode.
+	 */
+	if (event == PTRACE_EVENT_VFORK_DONE)
+		return UTRACE_REPORT;
+	else
+		return UTRACE_STOP;
+}
+
+static inline void set_syscall_code(struct ptrace_context *ctx)
+{
+	set_stop_code(ctx, PTRACE_EVENT_SYSCALL);
+	if (ctx->options & PTRACE_O_TRACESYSGOOD)
+		ctx->stop_code |= 0x80;
+}
+
+static u32 ptrace_report_syscall_entry(u32 action, struct utrace_engine *engine,
+				       struct pt_regs *regs)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+
+	if (action & UTRACE_SYSCALL_RESUMED) {
+		/*
+		 * We already reported the first time.
+		 * Nothing more to do now.
+		 */
+		if (unlikely(ctx->options & PTRACE_O_SYSEMU))
+			return UTRACE_SYSCALL_ABORT | UTRACE_REPORT;
+		return utrace_syscall_action(action) | UTRACE_RESUME;
+	}
+
+	WARN_ON(ptrace_event_pending(ctx));
+
+	set_syscall_code(ctx);
+
+	if (unlikely(ctx->options & PTRACE_O_SYSEMU))
+		return UTRACE_SYSCALL_ABORT | UTRACE_REPORT;
+	/*
+	 * Stop now to report.  We will get another callback after
+	 * we resume, with the UTRACE_SYSCALL_RESUMED flag set.
+	 */
+	return UTRACE_SYSCALL_RUN | UTRACE_STOP;
+}
+
+static u32 ptrace_report_syscall_exit(u32 action, struct utrace_engine *engine,
+				      struct pt_regs *regs)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+
+	if (ptrace_event_pending(ctx))
+		return UTRACE_STOP;
+
+	if (ctx->resume != UTRACE_RESUME) {
+		WARN_ON(ctx->resume != UTRACE_BLOCKSTEP &&
+			ctx->resume != UTRACE_SINGLESTEP);
+		ctx->resume = UTRACE_RESUME;
+
+		ctx->signr = SIGTRAP;
+		return UTRACE_INTERRUPT;
+	}
+
+	set_syscall_code(ctx);
+	return UTRACE_STOP;
+}
+
+static u32 ptrace_report_exec(u32 action, struct utrace_engine *engine,
+			      const struct linux_binfmt *fmt,
+			      const struct linux_binprm *bprm,
+			      struct pt_regs *regs)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+
+	WARN_ON(ptrace_event_pending(ctx));
+
+	if (!(ctx->options & PTRACE_O_TRACEEXEC)) {
+		/*
+		 * Old-fashioned ptrace'd exec just posts a plain signal.
+		 */
+		send_sig(SIGTRAP, current, 0);
+		return UTRACE_RESUME;
+	}
+
+	set_stop_code(ctx, PTRACE_EVENT_EXEC);
+	return UTRACE_STOP;
+}
+
+static enum utrace_signal_action resume_signal(struct ptrace_context *ctx,
+					       struct k_sigaction *return_ka)
+{
+	siginfo_t *info = ctx->siginfo;
+	int signr = ctx->signr;
+
+	ctx->siginfo = NULL;
+	ctx->signr = 0;
+
+	/* Did the debugger cancel the sig? */
+	if (!signr)
+		return UTRACE_SIGNAL_IGN;
+	/*
+	 * Update the siginfo structure if the signal has changed.
+	 * If the debugger wanted something specific in the siginfo
+	 * then it should have updated *info via PTRACE_SETSIGINFO.
+	 */
+	if (info->si_signo != signr) {
+		info->si_signo = signr;
+		info->si_errno = 0;
+		info->si_code = SI_USER;
+		info->si_pid = task_pid_vnr(current->parent);
+		info->si_uid = task_uid(current->parent);
+	}
+
+	/* If the (new) signal is now blocked, requeue it. */
+	if (sigismember(&current->blocked, signr)) {
+		send_sig_info(signr, info, current);
+		return UTRACE_SIGNAL_IGN;
+	}
+
+	spin_lock_irq(&current->sighand->siglock);
+	*return_ka = current->sighand->action[signr - 1];
+	spin_unlock_irq(&current->sighand->siglock);
+
+	return UTRACE_SIGNAL_DELIVER;
+}
+
+static u32 ptrace_report_signal(u32 action, struct utrace_engine *engine,
+				struct pt_regs *regs,
+				siginfo_t *info,
+				const struct k_sigaction *orig_ka,
+				struct k_sigaction *return_ka)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+	enum utrace_resume_action resume = ctx->resume;
+
+	if (ptrace_event_pending(ctx)) {
+		action = utrace_signal_action(action);
+		WARN_ON(action != UTRACE_SIGNAL_REPORT);
+		return action | UTRACE_STOP;
+	}
+
+	switch (utrace_signal_action(action)) {
+	case UTRACE_SIGNAL_HANDLER:
+		if (WARN_ON(ctx->siginfo))
+			ctx->siginfo = NULL;
+
+		if (resume != UTRACE_RESUME) {
+			WARN_ON(resume != UTRACE_BLOCKSTEP &&
+				resume != UTRACE_SINGLESTEP);
+
+			set_stop_code(ctx, PTRACE_EVENT_SIGTRAP);
+			return UTRACE_STOP | UTRACE_SIGNAL_IGN;
+		}
+
+	case UTRACE_SIGNAL_REPORT:
+		if (!ctx->siginfo) {
+			if (ctx->signr) {
+				/* set by ptrace_resume(SYSCALL_EXIT) */
+				WARN_ON(ctx->signr != SIGTRAP);
+				user_single_step_siginfo(current, regs, info);
+				force_sig_info(SIGTRAP, info, current);
+			}
+
+			return resume | UTRACE_SIGNAL_IGN;
+		}
+
+		if (WARN_ON(ctx->siginfo != info))
+			return resume | UTRACE_SIGNAL_IGN;
+
+		return resume | resume_signal(ctx, return_ka);
+
+	default:
+		break;
+	}
+
+	WARN_ON(ctx->siginfo);
+	ctx->siginfo = info;
+	/*
+	 * ctx->siginfo points to the caller's stack.
+	 * Make sure the subsequent UTRACE_SIGNAL_REPORT clears
+	 * ->siginfo before return from get_signal_to_deliver().
+	 */
+	if (utrace_control(current, engine, UTRACE_INTERRUPT))
+		WARN_ON(1);
+
+	ctx->signr = info->si_signo;
+	ctx->stop_code = (PTRACE_EVENT_SIGNAL << 8) | ctx->signr;
+
+	return UTRACE_STOP | UTRACE_SIGNAL_IGN;
+}
+
+static u32 ptrace_report_quiesce(u32 action, struct utrace_engine *engine,
+				 unsigned long event)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+
+	if (ptrace_event_pending(ctx))
+		return UTRACE_STOP;
+
+	return event ? UTRACE_RESUME : ctx->resume;
+}
+
+static void ptrace_release(void *data)
+{
+	kfree(data);
+}
+
+static const struct utrace_engine_ops ptrace_utrace_ops = {
+	.report_signal = ptrace_report_signal,
+	.report_quiesce = ptrace_report_quiesce,
+	.report_exec = ptrace_report_exec,
+	.report_exit = ptrace_report_exit,
+	.report_clone = ptrace_report_clone,
+	.report_syscall_entry = ptrace_report_syscall_entry,
+	.report_syscall_exit = ptrace_report_syscall_exit,
+	.release = ptrace_release,
+};
+
+int ptrace_check_attach(struct task_struct *child, int kill)
+{
+	struct utrace_engine *engine;
+	struct utrace_examiner exam;
+	int ret = -ESRCH;
+
+	engine = ptrace_lookup_engine(child);
+	if (IS_ERR(engine))
+		return ret;
+
+	if (child->parent != current)
+		goto out;
+
+	if (unlikely(kill))
+		ret = 0;
+
+	if (!task_is_stopped_or_traced(child))
+		goto out;
+	/*
+	 * Make sure our engine has already stopped the child.
+	 * Then wait for it to be off the CPU.
+	 */
+	if (!utrace_control(child, engine, UTRACE_STOP) &&
+	    !utrace_prepare_examine(child, engine, &exam))
+		ret = 0;
+out:
+	utrace_engine_put(engine);
+	return ret;
+}
+
+int ptrace_attach(struct task_struct *task)
+{
+	int retval;
+
+	audit_ptrace(task);
+
+	retval = -EPERM;
+	if (unlikely(task->flags & PF_KTHREAD))
+		goto out;
+	if (same_thread_group(task, current))
+		goto out;
+
+	/*
+	 * Protect exec's credential calculations against our interference;
+	 * interference; SUID, SGID and LSM creds get determined differently
+	 * under ptrace.
+	 */
+	retval = -ERESTARTNOINTR;
+	if (mutex_lock_interruptible(&task->cred_guard_mutex))
+		goto out;
+
+	task_lock(task);
+	retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
+	task_unlock(task);
+	if (retval)
+		goto unlock_creds;
+
+	retval = ptrace_attach_task(task, 0);
+	if (unlikely(retval))
+		goto unlock_creds;
+
+	write_lock_irq(&tasklist_lock);
+	retval = -EPERM;
+	if (unlikely(task->exit_state))
+		goto unlock_tasklist;
+
+	BUG_ON(task->ptrace);
+	task->ptrace = PT_UTRACED;
+	if (capable(CAP_SYS_PTRACE))
+		task->ptrace |= PT_PTRACE_CAP;
+
+	__ptrace_link(task, current);
+	send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
+
+	retval = 0;
+unlock_tasklist:
+	write_unlock_irq(&tasklist_lock);
+unlock_creds:
+	mutex_unlock(&task->cred_guard_mutex);
+out:
+	return retval;
+}
+
+/*
+ * Performs checks and sets PT_UTRACED.
+ * Should be used by all ptrace implementations for PTRACE_TRACEME.
+ */
+int ptrace_traceme(void)
+{
+	bool detach = true;
+	int ret = ptrace_attach_task(current, 0);
+
+	if (unlikely(ret))
+		return ret;
+
+	ret = -EPERM;
+	write_lock_irq(&tasklist_lock);
+	BUG_ON(current->ptrace);
+	ret = security_ptrace_traceme(current->parent);
+	/*
+	 * Check PF_EXITING to ensure ->real_parent has not passed
+	 * exit_ptrace(). Otherwise we don't report the error but
+	 * pretend ->real_parent untraces us right after return.
+	 */
+	if (!ret && !(current->real_parent->flags & PF_EXITING)) {
+		current->ptrace = PT_UTRACED;
+		__ptrace_link(current, current->real_parent);
+		detach = false;
+	}
+	write_unlock_irq(&tasklist_lock);
+
+	if (detach)
+		ptrace_abort_attach(current);
+	return ret;
+}
+
+static void ptrace_do_detach(struct task_struct *tracee, unsigned int data)
+{
+	bool detach, release;
+
+	write_lock_irq(&tasklist_lock);
+	/*
+	 * This tracee can be already killed. Make sure de_thread() or
+	 * our sub-thread doing do_wait() didn't do release_task() yet.
+	 */
+	detach = tracee->ptrace != 0;
+	release = false;
+	if (likely(detach))
+		release = __ptrace_detach(current, tracee);
+	write_unlock_irq(&tasklist_lock);
+
+	if (unlikely(release))
+		release_task(tracee);
+	else if (likely(detach))
+		ptrace_detach_task(tracee, data);
+}
+
+int ptrace_detach(struct task_struct *child, unsigned int data)
+{
+	if (!valid_signal(data))
+		return -EIO;
+
+	ptrace_do_detach(child, data);
+
+	return 0;
+}
+
+/*
+ * Detach all tasks we were using ptrace on.
+ */
+void exit_ptrace(struct task_struct *tracer)
+{
+	for (;;) {
+		struct task_struct *tracee = NULL;
+
+		read_lock(&tasklist_lock);
+		if (!list_empty(&tracer->ptraced)) {
+			tracee = list_first_entry(&tracer->ptraced,
+					struct task_struct, ptrace_entry);
+			get_task_struct(tracee);
+		}
+		read_unlock(&tasklist_lock);
+		if (!tracee)
+			break;
+
+		ptrace_do_detach(tracee, -1);
+		put_task_struct(tracee);
+	}
+}
+
+static int ptrace_set_options(struct task_struct *tracee,
+				struct utrace_engine *engine, long data)
+{
+	BUILD_BUG_ON(PTRACE_O_MASK & PTRACE_O_SYSEMU);
+
+	ptrace_set_events(tracee, engine, data & PTRACE_O_MASK);
+	return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
+}
+
+static int ptrace_rw_siginfo(struct task_struct *tracee,
+				struct ptrace_context *ctx,
+				siginfo_t *info, bool write)
+{
+	unsigned long flags;
+	int err;
+
+	switch (get_stop_event(ctx)) {
+	case 0: /* jctl stop */
+		return -EINVAL;
+
+	case PTRACE_EVENT_SIGNAL:
+		err = -ESRCH;
+		if (lock_task_sighand(tracee, &flags)) {
+			if (likely(task_is_traced(tracee))) {
+				if (write)
+					*ctx->siginfo = *info;
+				else
+					*info = *ctx->siginfo;
+				err = 0;
+			}
+			unlock_task_sighand(tracee, &flags);
+		}
+
+		return err;
+
+	default:
+		if (!write) {
+			memset(info, 0, sizeof(*info));
+			info->si_signo = SIGTRAP;
+			info->si_code = ctx->stop_code & PTRACE_EVENT_MASK;
+			info->si_pid = task_pid_vnr(tracee);
+			info->si_uid = task_uid(tracee);
+		}
+
+		return 0;
+	}
+}
+
+static void do_ptrace_notify_stop(struct ptrace_context *ctx,
+					struct task_struct *tracee)
+{
+	/*
+	 * This can race with SIGKILL, but we borrow this race from
+	 * the old ptrace implementation. ->exit_code is only needed
+	 * for wait_task_stopped()->task_stopped_code(), we should
+	 * change it to use ptrace_context.
+	 */
+	tracee->exit_code = ctx->stop_code & PTRACE_EVENT_MASK;
+	WARN_ON(!tracee->exit_code);
+
+	read_lock(&tasklist_lock);
+	/*
+	 * Don't want to allow preemption here, because
+	 * sys_ptrace() needs this task to be inactive.
+	 */
+	preempt_disable();
+	/*
+	 * It can be killed and then released by our subthread,
+	 * or ptrace_attach() has not completed yet.
+	 */
+	if (task_ptrace(tracee))
+		do_notify_parent_cldstop(tracee, CLD_TRAPPED);
+	read_unlock(&tasklist_lock);
+	preempt_enable_no_resched();
+}
+
+void ptrace_notify_stop(struct task_struct *tracee)
+{
+	struct utrace_engine *engine = ptrace_lookup_engine(tracee);
+
+	if (IS_ERR(engine))
+		return;
+
+	do_ptrace_notify_stop(ptrace_context(engine), tracee);
+	utrace_engine_put(engine);
+}
+
+static int ptrace_resume_action(struct task_struct *tracee,
+				struct utrace_engine *engine, long request)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+	unsigned long events;
+	int action;
+
+	ctx->options &= ~PTRACE_O_SYSEMU;
+	events = engine->flags & ~UTRACE_EVENT_SYSCALL;
+	action = UTRACE_RESUME;
+
+	switch (request) {
+#ifdef PTRACE_SINGLEBLOCK
+	case PTRACE_SINGLEBLOCK:
+		if (unlikely(!arch_has_block_step()))
+			return -EIO;
+		action = UTRACE_BLOCKSTEP;
+		events |= UTRACE_EVENT(SYSCALL_EXIT);
+		break;
+#endif
+
+#ifdef PTRACE_SINGLESTEP
+	case PTRACE_SINGLESTEP:
+		if (unlikely(!arch_has_single_step()))
+			return -EIO;
+		action = UTRACE_SINGLESTEP;
+		events |= UTRACE_EVENT(SYSCALL_EXIT);
+		break;
+#endif
+
+#ifdef PTRACE_SYSEMU
+	case PTRACE_SYSEMU_SINGLESTEP:
+		if (unlikely(!arch_has_single_step()))
+			return -EIO;
+		action = UTRACE_SINGLESTEP;
+	case PTRACE_SYSEMU:
+		ctx->options |= PTRACE_O_SYSEMU;
+		events |= UTRACE_EVENT(SYSCALL_ENTRY);
+		break;
+#endif
+
+	case PTRACE_SYSCALL:
+		events |= UTRACE_EVENT_SYSCALL;
+		break;
+
+	case PTRACE_CONT:
+		break;
+	default:
+		return -EIO;
+	}
+
+	if (events != engine->flags &&
+	    utrace_set_events(tracee, engine, events))
+		return -ESRCH;
+
+	return action;
+}
+
+static int ptrace_resume(struct task_struct *tracee,
+				struct utrace_engine *engine,
+				long request, long data)
+{
+	struct ptrace_context *ctx = ptrace_context(engine);
+	int action;
+
+	if (!valid_signal(data))
+		return -EIO;
+
+	action = ptrace_resume_action(tracee, engine, request);
+	if (action < 0)
+		return action;
+
+	switch (get_stop_event(ctx)) {
+	case PTRACE_EVENT_VFORK:
+		if (ctx->options & PTRACE_O_TRACEVFORKDONE) {
+			set_stop_code(ctx, PTRACE_EVENT_VFORK_DONE);
+			action = UTRACE_REPORT;
+		}
+		break;
+
+	case PTRACE_EVENT_EXEC:
+	case PTRACE_EVENT_FORK:
+	case PTRACE_EVENT_CLONE:
+	case PTRACE_EVENT_VFORK_DONE:
+		if (request == PTRACE_SYSCALL) {
+			set_syscall_code(ctx);
+			do_ptrace_notify_stop(ctx, tracee);
+			return 0;
+		}
+
+		if (action != UTRACE_RESUME) {
+			/*
+			 * single-stepping. UTRACE_SIGNAL_REPORT will
+			 * synthesize a trap to follow the syscall insn.
+			*/
+			ctx->signr = SIGTRAP;
+			action = UTRACE_INTERRUPT;
+		}
+		break;
+
+	case PTRACE_EVENT_SYSCALL:
+		if (data)
+			send_sig_info(data, SEND_SIG_PRIV, tracee);
+		break;
+
+	case PTRACE_EVENT_SIGNAL:
+		ctx->signr = data;
+		break;
+	}
+
+	ctx->resume = action;
+	ptrace_wake_up(tracee, engine, action, true);
+	return 0;
+}
+
+int ptrace_request(struct task_struct *child, long request,
+		   long addr, long data)
+{
+	struct utrace_engine *engine = ptrace_lookup_engine(child);
+	siginfo_t siginfo;
+	int ret;
+
+	if (unlikely(IS_ERR(engine)))
+		return -ESRCH;
+
+	switch (request) {
+	case PTRACE_PEEKTEXT:
+	case PTRACE_PEEKDATA:
+		ret = generic_ptrace_peekdata(child, addr, data);
+		break;
+	case PTRACE_POKETEXT:
+	case PTRACE_POKEDATA:
+		ret = generic_ptrace_pokedata(child, addr, data);
+		break;
+
+#ifdef PTRACE_OLDSETOPTIONS
+	case PTRACE_OLDSETOPTIONS:
+#endif
+	case PTRACE_SETOPTIONS:
+		ret = ptrace_set_options(child, engine, data);
+		break;
+	case PTRACE_GETEVENTMSG:
+		ret = put_user(ptrace_context(engine)->eventmsg,
+				(unsigned long __user *) data);
+		break;
+
+	case PTRACE_GETSIGINFO:
+		ret = ptrace_rw_siginfo(child, ptrace_context(engine),
+					&siginfo, false);
+		if (!ret)
+			ret = copy_siginfo_to_user((siginfo_t __user *) data,
+						   &siginfo);
+		break;
+
+	case PTRACE_SETSIGINFO:
+		if (copy_from_user(&siginfo, (siginfo_t __user *) data,
+				   sizeof siginfo))
+			ret = -EFAULT;
+		else
+			ret = ptrace_rw_siginfo(child, ptrace_context(engine),
+						&siginfo, true);
+		break;
+
+	case PTRACE_DETACH:	 /* detach a process that was attached. */
+		ret = ptrace_detach(child, data);
+		break;
+
+	case PTRACE_KILL:
+		/* Ugly historical behaviour. */
+		if (task_is_traced(child))
+			ptrace_resume(child, engine, PTRACE_CONT, SIGKILL);
+		ret = 0;
+		break;
+
+	default:
+		ret = ptrace_resume(child, engine, request, data);
+		break;
+	}
+
+	utrace_engine_put(engine);
+	return ret;
+}
+
+#if defined CONFIG_COMPAT
+#include <linux/compat.h>
+
+int compat_ptrace_request(struct task_struct *child, compat_long_t request,
+			  compat_ulong_t addr, compat_ulong_t data)
+{
+	struct utrace_engine *engine = ptrace_lookup_engine(child);
+	compat_ulong_t __user *datap = compat_ptr(data);
+	compat_ulong_t word;
+	siginfo_t siginfo;
+	int ret;
+
+	if (unlikely(IS_ERR(engine)))
+		return -ESRCH;
+
+	switch (request) {
+	case PTRACE_PEEKTEXT:
+	case PTRACE_PEEKDATA:
+		ret = access_process_vm(child, addr, &word, sizeof(word), 0);
+		if (ret != sizeof(word))
+			ret = -EIO;
+		else
+			ret = put_user(word, datap);
+		break;
+
+	case PTRACE_POKETEXT:
+	case PTRACE_POKEDATA:
+		ret = access_process_vm(child, addr, &data, sizeof(data), 1);
+		ret = (ret != sizeof(data) ? -EIO : 0);
+		break;
+
+	case PTRACE_GETEVENTMSG:
+		ret = put_user((compat_ulong_t)ptrace_context(engine)->eventmsg,
+				datap);
+		break;
+
+	case PTRACE_GETSIGINFO:
+		ret = ptrace_rw_siginfo(child, ptrace_context(engine),
+					&siginfo, false);
+		if (!ret)
+			ret = copy_siginfo_to_user32(
+				(struct compat_siginfo __user *) datap,
+				&siginfo);
+		break;
+
+	case PTRACE_SETSIGINFO:
+		memset(&siginfo, 0, sizeof siginfo);
+		if (copy_siginfo_from_user32(
+			    &siginfo, (struct compat_siginfo __user *) datap))
+			ret = -EFAULT;
+		else
+			ret = ptrace_rw_siginfo(child, ptrace_context(engine),
+						&siginfo, true);
+		break;
+
+	default:
+		ret = ptrace_request(child, request, addr, data);
+	}
+
+	utrace_engine_put(engine);
+	return ret;
+}
+#endif	/* CONFIG_COMPAT */