linux/include/linux/tracehook.h
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   1/*
   2 * Tracing hooks
   3 *
   4 * Copyright (C) 2008-2009 Red Hat, Inc.  All rights reserved.
   5 *
   6 * This copyrighted material is made available to anyone wishing to use,
   7 * modify, copy, or redistribute it subject to the terms and conditions
   8 * of the GNU General Public License v.2.
   9 *
  10 * This file defines hook entry points called by core code where
  11 * user tracing/debugging support might need to do something.  These
  12 * entry points are called tracehook_*().  Each hook declared below
  13 * has a detailed kerneldoc comment giving the context (locking et
  14 * al) from which it is called, and the meaning of its return value.
  15 *
  16 * Each function here typically has only one call site, so it is ok
  17 * to have some nontrivial tracehook_*() inlines.  In all cases, the
  18 * fast path when no tracing is enabled should be very short.
  19 *
  20 * The purpose of this file and the tracehook_* layer is to consolidate
  21 * the interface that the kernel core and arch code uses to enable any
  22 * user debugging or tracing facility (such as ptrace).  The interfaces
  23 * here are carefully documented so that maintainers of core and arch
  24 * code do not need to think about the implementation details of the
  25 * tracing facilities.  Likewise, maintainers of the tracing code do not
  26 * need to understand all the calling core or arch code in detail, just
  27 * documented circumstances of each call, such as locking conditions.
  28 *
  29 * If the calling core code changes so that locking is different, then
  30 * it is ok to change the interface documented here.  The maintainer of
  31 * core code changing should notify the maintainers of the tracing code
  32 * that they need to work out the change.
  33 *
  34 * Some tracehook_*() inlines take arguments that the current tracing
  35 * implementations might not necessarily use.  These function signatures
  36 * are chosen to pass in all the information that is on hand in the
  37 * caller and might conceivably be relevant to a tracer, so that the
  38 * core code won't have to be updated when tracing adds more features.
  39 * If a call site changes so that some of those parameters are no longer
  40 * already on hand without extra work, then the tracehook_* interface
  41 * can change so there is no make-work burden on the core code.  The
  42 * maintainer of core code changing should notify the maintainers of the
  43 * tracing code that they need to work out the change.
  44 */
  45
  46#ifndef _LINUX_TRACEHOOK_H
  47#define _LINUX_TRACEHOOK_H      1
  48
  49#include <linux/sched.h>
  50#include <linux/ptrace.h>
  51#include <linux/security.h>
  52#include <linux/task_work.h>
  53struct linux_binprm;
  54
  55/*
  56 * ptrace report for syscall entry and exit looks identical.
  57 */
  58static inline int ptrace_report_syscall(struct pt_regs *regs)
  59{
  60        int ptrace = current->ptrace;
  61
  62        if (!(ptrace & PT_PTRACED))
  63                return 0;
  64
  65        ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
  66
  67        /*
  68         * this isn't the same as continuing with a signal, but it will do
  69         * for normal use.  strace only continues with a signal if the
  70         * stopping signal is not SIGTRAP.  -brl
  71         */
  72        if (current->exit_code) {
  73                send_sig(current->exit_code, current, 1);
  74                current->exit_code = 0;
  75        }
  76
  77        return fatal_signal_pending(current);
  78}
  79
  80/**
  81 * tracehook_report_syscall_entry - task is about to attempt a system call
  82 * @regs:               user register state of current task
  83 *
  84 * This will be called if %TIF_SYSCALL_TRACE has been set, when the
  85 * current task has just entered the kernel for a system call.
  86 * Full user register state is available here.  Changing the values
  87 * in @regs can affect the system call number and arguments to be tried.
  88 * It is safe to block here, preventing the system call from beginning.
  89 *
  90 * Returns zero normally, or nonzero if the calling arch code should abort
  91 * the system call.  That must prevent normal entry so no system call is
  92 * made.  If @task ever returns to user mode after this, its register state
  93 * is unspecified, but should be something harmless like an %ENOSYS error
  94 * return.  It should preserve enough information so that syscall_rollback()
  95 * can work (see asm-generic/syscall.h).
  96 *
  97 * Called without locks, just after entering kernel mode.
  98 */
  99static inline __must_check int tracehook_report_syscall_entry(
 100        struct pt_regs *regs)
 101{
 102        return ptrace_report_syscall(regs);
 103}
 104
 105/**
 106 * tracehook_report_syscall_exit - task has just finished a system call
 107 * @regs:               user register state of current task
 108 * @step:               nonzero if simulating single-step or block-step
 109 *
 110 * This will be called if %TIF_SYSCALL_TRACE has been set, when the
 111 * current task has just finished an attempted system call.  Full
 112 * user register state is available here.  It is safe to block here,
 113 * preventing signals from being processed.
 114 *
 115 * If @step is nonzero, this report is also in lieu of the normal
 116 * trap that would follow the system call instruction because
 117 * user_enable_block_step() or user_enable_single_step() was used.
 118 * In this case, %TIF_SYSCALL_TRACE might not be set.
 119 *
 120 * Called without locks, just before checking for pending signals.
 121 */
 122static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
 123{
 124        if (step) {
 125                siginfo_t info;
 126                user_single_step_siginfo(current, regs, &info);
 127                force_sig_info(SIGTRAP, &info, current);
 128                return;
 129        }
 130
 131        ptrace_report_syscall(regs);
 132}
 133
 134/**
 135 * tracehook_signal_handler - signal handler setup is complete
 136 * @sig:                number of signal being delivered
 137 * @info:               siginfo_t of signal being delivered
 138 * @ka:                 sigaction setting that chose the handler
 139 * @regs:               user register state
 140 * @stepping:           nonzero if debugger single-step or block-step in use
 141 *
 142 * Called by the arch code after a signal handler has been set up.
 143 * Register and stack state reflects the user handler about to run.
 144 * Signal mask changes have already been made.
 145 *
 146 * Called without locks, shortly before returning to user mode
 147 * (or handling more signals).
 148 */
 149static inline void tracehook_signal_handler(int sig, siginfo_t *info,
 150                                            const struct k_sigaction *ka,
 151                                            struct pt_regs *regs, int stepping)
 152{
 153        if (stepping)
 154                ptrace_notify(SIGTRAP);
 155}
 156
 157/**
 158 * set_notify_resume - cause tracehook_notify_resume() to be called
 159 * @task:               task that will call tracehook_notify_resume()
 160 *
 161 * Calling this arranges that @task will call tracehook_notify_resume()
 162 * before returning to user mode.  If it's already running in user mode,
 163 * it will enter the kernel and call tracehook_notify_resume() soon.
 164 * If it's blocked, it will not be woken.
 165 */
 166static inline void set_notify_resume(struct task_struct *task)
 167{
 168#ifdef TIF_NOTIFY_RESUME
 169        if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
 170                kick_process(task);
 171#endif
 172}
 173
 174/**
 175 * tracehook_notify_resume - report when about to return to user mode
 176 * @regs:               user-mode registers of @current task
 177 *
 178 * This is called when %TIF_NOTIFY_RESUME has been set.  Now we are
 179 * about to return to user mode, and the user state in @regs can be
 180 * inspected or adjusted.  The caller in arch code has cleared
 181 * %TIF_NOTIFY_RESUME before the call.  If the flag gets set again
 182 * asynchronously, this will be called again before we return to
 183 * user mode.
 184 *
 185 * Called without locks.
 186 */
 187static inline void tracehook_notify_resume(struct pt_regs *regs)
 188{
 189        /*
 190         * The caller just cleared TIF_NOTIFY_RESUME. This barrier
 191         * pairs with task_work_add()->set_notify_resume() after
 192         * hlist_add_head(task->task_works);
 193         */
 194        smp_mb__after_clear_bit();
 195        if (unlikely(current->task_works))
 196                task_work_run();
 197}
 198
 199#endif  /* <linux/tracehook.h> */
 200
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