tracehook: syscall

[safe/jmp/linux-2.6] / include / linux / tracehook.h

/*
 * Tracing hooks
 *
 * Copyright (C) 2008 Red Hat, Inc.  All rights reserved.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU General Public License v.2.
 *
 * This file defines hook entry points called by core code where
 * user tracing/debugging support might need to do something.  These
 * entry points are called tracehook_*().  Each hook declared below
 * has a detailed kerneldoc comment giving the context (locking et
 * al) from which it is called, and the meaning of its return value.
 *
 * Each function here typically has only one call site, so it is ok
 * to have some nontrivial tracehook_*() inlines.  In all cases, the
 * fast path when no tracing is enabled should be very short.
 *
 * The purpose of this file and the tracehook_* layer is to consolidate
 * the interface that the kernel core and arch code uses to enable any
 * user debugging or tracing facility (such as ptrace).  The interfaces
 * here are carefully documented so that maintainers of core and arch
 * code do not need to think about the implementation details of the
 * tracing facilities.  Likewise, maintainers of the tracing code do not
 * need to understand all the calling core or arch code in detail, just
 * documented circumstances of each call, such as locking conditions.
 *
 * If the calling core code changes so that locking is different, then
 * it is ok to change the interface documented here.  The maintainer of
 * core code changing should notify the maintainers of the tracing code
 * that they need to work out the change.
 *
 * Some tracehook_*() inlines take arguments that the current tracing
 * implementations might not necessarily use.  These function signatures
 * are chosen to pass in all the information that is on hand in the
 * caller and might conceivably be relevant to a tracer, so that the
 * core code won't have to be updated when tracing adds more features.
 * If a call site changes so that some of those parameters are no longer
 * already on hand without extra work, then the tracehook_* interface
 * can change so there is no make-work burden on the core code.  The
 * maintainer of core code changing should notify the maintainers of the
 * tracing code that they need to work out the change.
 */

#ifndef _LINUX_TRACEHOOK_H
#define _LINUX_TRACEHOOK_H      1

#include <linux/sched.h>
#include <linux/ptrace.h>
#include <linux/security.h>
struct linux_binprm;

/**
 * tracehook_expect_breakpoints - guess if task memory might be touched
 * @task:               current task, making a new mapping
 *
 * Return nonzero if @task is expected to want breakpoint insertion in
 * its memory at some point.  A zero return is no guarantee it won't
 * be done, but this is a hint that it's known to be likely.
 *
 * May be called with @task->mm->mmap_sem held for writing.
 */
static inline int tracehook_expect_breakpoints(struct task_struct *task)
{
        return (task_ptrace(task) & PT_PTRACED) != 0;
}

/*
 * ptrace report for syscall entry and exit looks identical.
 */
static inline void ptrace_report_syscall(struct pt_regs *regs)
{
        int ptrace = task_ptrace(current);

        if (!(ptrace & PT_PTRACED))
                return;

        ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));

        /*
         * this isn't the same as continuing with a signal, but it will do
         * for normal use.  strace only continues with a signal if the
         * stopping signal is not SIGTRAP.  -brl
         */
        if (current->exit_code) {
                send_sig(current->exit_code, current, 1);
                current->exit_code = 0;
        }
}

/**
 * tracehook_report_syscall_entry - task is about to attempt a system call
 * @regs:               user register state of current task
 *
 * This will be called if %TIF_SYSCALL_TRACE has been set, when the
 * current task has just entered the kernel for a system call.
 * Full user register state is available here.  Changing the values
 * in @regs can affect the system call number and arguments to be tried.
 * It is safe to block here, preventing the system call from beginning.
 *
 * Returns zero normally, or nonzero if the calling arch code should abort
 * the system call.  That must prevent normal entry so no system call is
 * made.  If @task ever returns to user mode after this, its register state
 * is unspecified, but should be something harmless like an %ENOSYS error
 * return.
 *
 * Called without locks, just after entering kernel mode.
 */
static inline __must_check int tracehook_report_syscall_entry(
        struct pt_regs *regs)
{
        ptrace_report_syscall(regs);
        return 0;
}

/**
 * tracehook_report_syscall_exit - task has just finished a system call
 * @regs:               user register state of current task
 * @step:               nonzero if simulating single-step or block-step
 *
 * This will be called if %TIF_SYSCALL_TRACE has been set, when the
 * current task has just finished an attempted system call.  Full
 * user register state is available here.  It is safe to block here,
 * preventing signals from being processed.
 *
 * If @step is nonzero, this report is also in lieu of the normal
 * trap that would follow the system call instruction because
 * user_enable_block_step() or user_enable_single_step() was used.
 * In this case, %TIF_SYSCALL_TRACE might not be set.
 *
 * Called without locks, just before checking for pending signals.
 */
static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
{
        ptrace_report_syscall(regs);
}

/**
 * tracehook_unsafe_exec - check for exec declared unsafe due to tracing
 * @task:               current task doing exec
 *
 * Return %LSM_UNSAFE_* bits applied to an exec because of tracing.
 *
 * Called with task_lock() held on @task.
 */
static inline int tracehook_unsafe_exec(struct task_struct *task)
{
        int unsafe = 0;
        int ptrace = task_ptrace(task);
        if (ptrace & PT_PTRACED) {
                if (ptrace & PT_PTRACE_CAP)
                        unsafe |= LSM_UNSAFE_PTRACE_CAP;
                else
                        unsafe |= LSM_UNSAFE_PTRACE;
        }
        return unsafe;
}

/**
 * tracehook_tracer_task - return the task that is tracing the given task
 * @tsk:                task to consider
 *
 * Returns NULL if noone is tracing @task, or the &struct task_struct
 * pointer to its tracer.
 *
 * Must called under rcu_read_lock().  The pointer returned might be kept
 * live only by RCU.  During exec, this may be called with task_lock()
 * held on @task, still held from when tracehook_unsafe_exec() was called.
 */
static inline struct task_struct *tracehook_tracer_task(struct task_struct *tsk)
{
        if (task_ptrace(tsk) & PT_PTRACED)
                return rcu_dereference(tsk->parent);
        return NULL;
}

/**
 * tracehook_report_exec - a successful exec was completed
 * @fmt:                &struct linux_binfmt that performed the exec
 * @bprm:               &struct linux_binprm containing exec details
 * @regs:               user-mode register state
 *
 * An exec just completed, we are shortly going to return to user mode.
 * The freshly initialized register state can be seen and changed in @regs.
 * The name, file and other pointers in @bprm are still on hand to be
 * inspected, but will be freed as soon as this returns.
 *
 * Called with no locks, but with some kernel resources held live
 * and a reference on @fmt->module.
 */
static inline void tracehook_report_exec(struct linux_binfmt *fmt,
                                         struct linux_binprm *bprm,
                                         struct pt_regs *regs)
{
        if (!ptrace_event(PT_TRACE_EXEC, PTRACE_EVENT_EXEC, 0) &&
            unlikely(task_ptrace(current) & PT_PTRACED))
                send_sig(SIGTRAP, current, 0);
}

/**
 * tracehook_report_exit - task has begun to exit
 * @exit_code:          pointer to value destined for @current->exit_code
 *
 * @exit_code points to the value passed to do_exit(), which tracing
 * might change here.  This is almost the first thing in do_exit(),
 * before freeing any resources or setting the %PF_EXITING flag.
 *
 * Called with no locks held.
 */
static inline void tracehook_report_exit(long *exit_code)
{
        ptrace_event(PT_TRACE_EXIT, PTRACE_EVENT_EXIT, *exit_code);
}

/**
 * tracehook_prepare_clone - prepare for new child to be cloned
 * @clone_flags:        %CLONE_* flags from clone/fork/vfork system call
 *
 * This is called before a new user task is to be cloned.
 * Its return value will be passed to tracehook_finish_clone().
 *
 * Called with no locks held.
 */
static inline int tracehook_prepare_clone(unsigned clone_flags)
{
        if (clone_flags & CLONE_UNTRACED)
                return 0;

        if (clone_flags & CLONE_VFORK) {
                if (current->ptrace & PT_TRACE_VFORK)
                        return PTRACE_EVENT_VFORK;
        } else if ((clone_flags & CSIGNAL) != SIGCHLD) {
                if (current->ptrace & PT_TRACE_CLONE)
                        return PTRACE_EVENT_CLONE;
        } else if (current->ptrace & PT_TRACE_FORK)
                return PTRACE_EVENT_FORK;

        return 0;
}

/**
 * tracehook_finish_clone - new child created and being attached
 * @child:              new child task
 * @clone_flags:        %CLONE_* flags from clone/fork/vfork system call
 * @trace:              return value from tracehook_clone_prepare()
 *
 * This is called immediately after adding @child to its parent's children list.
 * The @trace value is that returned by tracehook_prepare_clone().
 *
 * Called with current's siglock and write_lock_irq(&tasklist_lock) held.
 */
static inline void tracehook_finish_clone(struct task_struct *child,
                                          unsigned long clone_flags, int trace)
{
        ptrace_init_task(child, (clone_flags & CLONE_PTRACE) || trace);
}

/**
 * tracehook_report_clone - in parent, new child is about to start running
 * @trace:              return value from tracehook_clone_prepare()
 * @regs:               parent's user register state
 * @clone_flags:        flags from parent's system call
 * @pid:                new child's PID in the parent's namespace
 * @child:              new child task
 *
 * Called after a child is set up, but before it has been started running.
 * The @trace value is that returned by tracehook_clone_prepare().
 * This is not a good place to block, because the child has not started yet.
 * Suspend the child here if desired, and block in tracehook_clone_complete().
 * This must prevent the child from self-reaping if tracehook_clone_complete()
 * uses the @child pointer; otherwise it might have died and been released by
 * the time tracehook_report_clone_complete() is called.
 *
 * Called with no locks held, but the child cannot run until this returns.
 */
static inline void tracehook_report_clone(int trace, struct pt_regs *regs,
                                          unsigned long clone_flags,
                                          pid_t pid, struct task_struct *child)
{
        if (unlikely(trace)) {
                /*
                 * The child starts up with an immediate SIGSTOP.
                 */
                sigaddset(&child->pending.signal, SIGSTOP);
                set_tsk_thread_flag(child, TIF_SIGPENDING);
        }
}

/**
 * tracehook_report_clone_complete - new child is running
 * @trace:              return value from tracehook_clone_prepare()
 * @regs:               parent's user register state
 * @clone_flags:        flags from parent's system call
 * @pid:                new child's PID in the parent's namespace
 * @child:              child task, already running
 *
 * This is called just after the child has started running.  This is
 * just before the clone/fork syscall returns, or blocks for vfork
 * child completion if @clone_flags has the %CLONE_VFORK bit set.
 * The @child pointer may be invalid if a self-reaping child died and
 * tracehook_report_clone() took no action to prevent it from self-reaping.
 *
 * Called with no locks held.
 */
static inline void tracehook_report_clone_complete(int trace,
                                                   struct pt_regs *regs,
                                                   unsigned long clone_flags,
                                                   pid_t pid,
                                                   struct task_struct *child)
{
        if (unlikely(trace))
                ptrace_event(0, trace, pid);
}

/**
 * tracehook_report_vfork_done - vfork parent's child has exited or exec'd
 * @child:              child task, already running
 * @pid:                new child's PID in the parent's namespace
 *
 * Called after a %CLONE_VFORK parent has waited for the child to complete.
 * The clone/vfork system call will return immediately after this.
 * The @child pointer may be invalid if a self-reaping child died and
 * tracehook_report_clone() took no action to prevent it from self-reaping.
 *
 * Called with no locks held.
 */
static inline void tracehook_report_vfork_done(struct task_struct *child,
                                               pid_t pid)
{
        ptrace_event(PT_TRACE_VFORK_DONE, PTRACE_EVENT_VFORK_DONE, pid);
}

/**
 * tracehook_prepare_release_task - task is being reaped, clean up tracing
 * @task:               task in %EXIT_DEAD state
 *
 * This is called in release_task() just before @task gets finally reaped
 * and freed.  This would be the ideal place to remove and clean up any
 * tracing-related state for @task.
 *
 * Called with no locks held.
 */
static inline void tracehook_prepare_release_task(struct task_struct *task)
{
}

/**
 * tracehook_finish_release_task - task is being reaped, clean up tracing
 * @task:               task in %EXIT_DEAD state
 *
 * This is called in release_task() when @task is being in the middle of
 * being reaped.  After this, there must be no tracing entanglements.
 *
 * Called with write_lock_irq(&tasklist_lock) held.
 */
static inline void tracehook_finish_release_task(struct task_struct *task)
{
        ptrace_release_task(task);
}

/**
 * tracehook_signal_handler - signal handler setup is complete
 * @sig:                number of signal being delivered
 * @info:               siginfo_t of signal being delivered
 * @ka:                 sigaction setting that chose the handler
 * @regs:               user register state
 * @stepping:           nonzero if debugger single-step or block-step in use
 *
 * Called by the arch code after a signal handler has been set up.
 * Register and stack state reflects the user handler about to run.
 * Signal mask changes have already been made.
 *
 * Called without locks, shortly before returning to user mode
 * (or handling more signals).
 */
static inline void tracehook_signal_handler(int sig, siginfo_t *info,
                                            const struct k_sigaction *ka,
                                            struct pt_regs *regs, int stepping)
{
        if (stepping)
                ptrace_notify(SIGTRAP);
}

/**
 * tracehook_consider_ignored_signal - suppress short-circuit of ignored signal
 * @task:               task receiving the signal
 * @sig:                signal number being sent
 * @handler:            %SIG_IGN or %SIG_DFL
 *
 * Return zero iff tracing doesn't care to examine this ignored signal,
 * so it can short-circuit normal delivery and never even get queued.
 * Either @handler is %SIG_DFL and @sig's default is ignore, or it's %SIG_IGN.
 *
 * Called with @task->sighand->siglock held.
 */
static inline int tracehook_consider_ignored_signal(struct task_struct *task,
                                                    int sig,
                                                    void __user *handler)
{
        return (task_ptrace(task) & PT_PTRACED) != 0;
}

/**
 * tracehook_consider_fatal_signal - suppress special handling of fatal signal
 * @task:               task receiving the signal
 * @sig:                signal number being sent
 * @handler:            %SIG_DFL or %SIG_IGN
 *
 * Return nonzero to prevent special handling of this termination signal.
 * Normally @handler is %SIG_DFL.  It can be %SIG_IGN if @sig is ignored,
 * in which case force_sig() is about to reset it to %SIG_DFL.
 * When this returns zero, this signal might cause a quick termination
 * that does not give the debugger a chance to intercept the signal.
 *
 * Called with or without @task->sighand->siglock held.
 */
static inline int tracehook_consider_fatal_signal(struct task_struct *task,
                                                  int sig,
                                                  void __user *handler)
{
        return (task_ptrace(task) & PT_PTRACED) != 0;
}

#endif  /* <linux/tracehook.h> */