include/linux/tracehook.h

   1 /*
   2  * Tracing hooks
   3  *
   4  * Copyright (C) 2008 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 struct linux_binprm;
  53
  54 /**
  55  * tracehook_unsafe_exec - check for exec declared unsafe due to tracing
  56  * @task:               current task doing exec
  57  *
  58  * Return %LSM_UNSAFE_* bits applied to an exec because of tracing.
  59  *
  60  * Called with task_lock() held on @task.
  61  */
  62 static inline int tracehook_unsafe_exec(struct task_struct *task)
  63 {
  64         int unsafe = 0;
  65         int ptrace = task_ptrace(task);
  66         if (ptrace & PT_PTRACED) {
  67                 if (ptrace & PT_PTRACE_CAP)
  68                         unsafe |= LSM_UNSAFE_PTRACE_CAP;
  69                 else
  70                         unsafe |= LSM_UNSAFE_PTRACE;
  71         }
  72         return unsafe;
  73 }
  74
  75 /**
  76  * tracehook_report_exec - a successful exec was completed
  77  * @fmt:                &struct linux_binfmt that performed the exec
  78  * @bprm:               &struct linux_binprm containing exec details
  79  * @regs:               user-mode register state
  80  *
  81  * An exec just completed, we are shortly going to return to user mode.
  82  * The freshly initialized register state can be seen and changed in @regs.
  83  * The name, file and other pointers in @bprm are still on hand to be
  84  * inspected, but will be freed as soon as this returns.
  85  *
  86  * Called with no locks, but with some kernel resources held live
  87  * and a reference on @fmt->module.
  88  */
  89 static inline void tracehook_report_exec(struct linux_binfmt *fmt,
  90                                          struct linux_binprm *bprm,
  91                                          struct pt_regs *regs)
  92 {
  93         if (!ptrace_event(PT_TRACE_EXEC, PTRACE_EVENT_EXEC, 0) &&
  94             unlikely(task_ptrace(current) & PT_PTRACED))
  95                 send_sig(SIGTRAP, current, 0);
  96 }
  97
  98 /**
  99  * tracehook_report_exit - task has begun to exit
 100  * @exit_code:          pointer to value destined for @current->exit_code
 101  *
 102  * @exit_code points to the value passed to do_exit(), which tracing
 103  * might change here.  This is almost the first thing in do_exit(),
 104  * before freeing any resources or setting the %PF_EXITING flag.
 105  *
 106  * Called with no locks held.
 107  */
 108 static inline void tracehook_report_exit(long *exit_code)
 109 {
 110         ptrace_event(PT_TRACE_EXIT, PTRACE_EVENT_EXIT, *exit_code);
 111 }
 112
 113 /**
 114  * tracehook_prepare_clone - prepare for new child to be cloned
 115  * @clone_flags:        %CLONE_* flags from clone/fork/vfork system call
 116  *
 117  * This is called before a new user task is to be cloned.
 118  * Its return value will be passed to tracehook_finish_clone().
 119  *
 120  * Called with no locks held.
 121  */
 122 static inline int tracehook_prepare_clone(unsigned clone_flags)
 123 {
 124         if (clone_flags & CLONE_UNTRACED)
 125                 return 0;
 126
 127         if (clone_flags & CLONE_VFORK) {
 128                 if (current->ptrace & PT_TRACE_VFORK)
 129                         return PTRACE_EVENT_VFORK;
 130         } else if ((clone_flags & CSIGNAL) != SIGCHLD) {
 131                 if (current->ptrace & PT_TRACE_CLONE)
 132                         return PTRACE_EVENT_CLONE;
 133         } else if (current->ptrace & PT_TRACE_FORK)
 134                 return PTRACE_EVENT_FORK;
 135
 136         return 0;
 137 }
 138
 139 /**
 140  * tracehook_finish_clone - new child created and being attached
 141  * @child:              new child task
 142  * @clone_flags:        %CLONE_* flags from clone/fork/vfork system call
 143  * @trace:              return value from tracehook_clone_prepare()
 144  *
 145  * This is called immediately after adding @child to its parent's children list.
 146  * The @trace value is that returned by tracehook_prepare_clone().
 147  *
 148  * Called with current's siglock and write_lock_irq(&tasklist_lock) held.
 149  */
 150 static inline void tracehook_finish_clone(struct task_struct *child,
 151                                           unsigned long clone_flags, int trace)
 152 {
 153         ptrace_init_task(child, (clone_flags & CLONE_PTRACE) || trace);
 154 }
 155
 156 /**
 157  * tracehook_report_clone - in parent, new child is about to start running
 158  * @trace:              return value from tracehook_clone_prepare()
 159  * @regs:               parent's user register state
 160  * @clone_flags:        flags from parent's system call
 161  * @pid:                new child's PID in the parent's namespace
 162  * @child:              new child task
 163  *
 164  * Called after a child is set up, but before it has been started running.
 165  * The @trace value is that returned by tracehook_clone_prepare().
 166  * This is not a good place to block, because the child has not started yet.
 167  * Suspend the child here if desired, and block in tracehook_clone_complete().
 168  * This must prevent the child from self-reaping if tracehook_clone_complete()
 169  * uses the @child pointer; otherwise it might have died and been released by
 170  * the time tracehook_report_clone_complete() is called.
 171  *
 172  * Called with no locks held, but the child cannot run until this returns.
 173  */
 174 static inline void tracehook_report_clone(int trace, struct pt_regs *regs,
 175                                           unsigned long clone_flags,
 176                                           pid_t pid, struct task_struct *child)
 177 {
 178         if (unlikely(trace)) {
 179                 /*
 180                  * The child starts up with an immediate SIGSTOP.
 181                  */
 182                 sigaddset(&child->pending.signal, SIGSTOP);
 183                 set_tsk_thread_flag(child, TIF_SIGPENDING);
 184         }
 185 }
 186
 187 /**
 188  * tracehook_report_clone_complete - new child is running
 189  * @trace:              return value from tracehook_clone_prepare()
 190  * @regs:               parent's user register state
 191  * @clone_flags:        flags from parent's system call
 192  * @pid:                new child's PID in the parent's namespace
 193  * @child:              child task, already running
 194  *
 195  * This is called just after the child has started running.  This is
 196  * just before the clone/fork syscall returns, or blocks for vfork
 197  * child completion if @clone_flags has the %CLONE_VFORK bit set.
 198  * The @child pointer may be invalid if a self-reaping child died and
 199  * tracehook_report_clone() took no action to prevent it from self-reaping.
 200  *
 201  * Called with no locks held.
 202  */
 203 static inline void tracehook_report_clone_complete(int trace,
 204                                                    struct pt_regs *regs,
 205                                                    unsigned long clone_flags,
 206                                                    pid_t pid,
 207                                                    struct task_struct *child)
 208 {
 209         if (unlikely(trace))
 210                 ptrace_event(0, trace, pid);
 211 }
 212
 213 /**
 214  * tracehook_report_vfork_done - vfork parent's child has exited or exec'd
 215  * @child:              child task, already running
 216  * @pid:                new child's PID in the parent's namespace
 217  *
 218  * Called after a %CLONE_VFORK parent has waited for the child to complete.
 219  * The clone/vfork system call will return immediately after this.
 220  * The @child pointer may be invalid if a self-reaping child died and
 221  * tracehook_report_clone() took no action to prevent it from self-reaping.
 222  *
 223  * Called with no locks held.
 224  */
 225 static inline void tracehook_report_vfork_done(struct task_struct *child,
 226                                                pid_t pid)
 227 {
 228         ptrace_event(PT_TRACE_VFORK_DONE, PTRACE_EVENT_VFORK_DONE, pid);
 229 }
 230
 231 #endif  /* <linux/tracehook.h> */