include/linux/tracehook.h

   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>
  53 #include <linux/memcontrol.h>
  54 #include <linux/blk-cgroup.h>
  55 struct linux_binprm;
  56
  57 /*
  58  * ptrace report for syscall entry and exit looks identical.
  59  */
  60 static inline int ptrace_report_syscall(struct pt_regs *regs)
  61 {
  62         int ptrace = current->ptrace;
  63
  64         if (!(ptrace & PT_PTRACED))
  65                 return 0;
  66
  67         ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
  68
  69         /*
  70          * this isn't the same as continuing with a signal, but it will do
  71          * for normal use.  strace only continues with a signal if the
  72          * stopping signal is not SIGTRAP.  -brl
  73          */
  74         if (current->exit_code) {
  75                 send_sig(current->exit_code, current, 1);
  76                 current->exit_code = 0;
  77         }
  78
  79         return fatal_signal_pending(current);
  80 }
  81
  82 /**
  83  * tracehook_report_syscall_entry - task is about to attempt a system call
  84  * @regs:               user register state of current task
  85  *
  86  * This will be called if %TIF_SYSCALL_TRACE or %TIF_SYSCALL_EMU have been set,
  87  * when the current task has just entered the kernel for a system call.
  88  * Full user register state is available here.  Changing the values
  89  * in @regs can affect the system call number and arguments to be tried.
  90  * It is safe to block here, preventing the system call from beginning.
  91  *
  92  * Returns zero normally, or nonzero if the calling arch code should abort
  93  * the system call.  That must prevent normal entry so no system call is
  94  * made.  If @task ever returns to user mode after this, its register state
  95  * is unspecified, but should be something harmless like an %ENOSYS error
  96  * return.  It should preserve enough information so that syscall_rollback()
  97  * can work (see asm-generic/syscall.h).
  98  *
  99  * Called without locks, just after entering kernel mode.
 100  */
 101 static inline __must_check int tracehook_report_syscall_entry(
 102         struct pt_regs *regs)
 103 {
 104         return ptrace_report_syscall(regs);
 105 }
 106
 107 /**
 108  * tracehook_report_syscall_exit - task has just finished a system call
 109  * @regs:               user register state of current task
 110  * @step:               nonzero if simulating single-step or block-step
 111  *
 112  * This will be called if %TIF_SYSCALL_TRACE has been set, when the
 113  * current task has just finished an attempted system call.  Full
 114  * user register state is available here.  It is safe to block here,
 115  * preventing signals from being processed.
 116  *
 117  * If @step is nonzero, this report is also in lieu of the normal
 118  * trap that would follow the system call instruction because
 119  * user_enable_block_step() or user_enable_single_step() was used.
 120  * In this case, %TIF_SYSCALL_TRACE might not be set.
 121  *
 122  * Called without locks, just before checking for pending signals.
 123  */
 124 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
 125 {
 126         if (step)
 127                 user_single_step_report(regs);
 128         else
 129                 ptrace_report_syscall(regs);
 130 }
 131
 132 /**
 133  * tracehook_signal_handler - signal handler setup is complete
 134  * @stepping:           nonzero if debugger single-step or block-step in use
 135  *
 136  * Called by the arch code after a signal handler has been set up.
 137  * Register and stack state reflects the user handler about to run.
 138  * Signal mask changes have already been made.
 139  *
 140  * Called without locks, shortly before returning to user mode
 141  * (or handling more signals).
 142  */
 143 static inline void tracehook_signal_handler(int stepping)
 144 {
 145         if (stepping)
 146                 ptrace_notify(SIGTRAP);
 147 }
 148
 149 /**
 150  * set_notify_resume - cause tracehook_notify_resume() to be called
 151  * @task:               task that will call tracehook_notify_resume()
 152  *
 153  * Calling this arranges that @task will call tracehook_notify_resume()
 154  * before returning to user mode.  If it's already running in user mode,
 155  * it will enter the kernel and call tracehook_notify_resume() soon.
 156  * If it's blocked, it will not be woken.
 157  */
 158 static inline void set_notify_resume(struct task_struct *task)
 159 {
 160 #ifdef TIF_NOTIFY_RESUME
 161         if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
 162                 kick_process(task);
 163 #endif
 164 }
 165
 166 /**
 167  * tracehook_notify_resume - report when about to return to user mode
 168  * @regs:               user-mode registers of @current task
 169  *
 170  * This is called when %TIF_NOTIFY_RESUME has been set.  Now we are
 171  * about to return to user mode, and the user state in @regs can be
 172  * inspected or adjusted.  The caller in arch code has cleared
 173  * %TIF_NOTIFY_RESUME before the call.  If the flag gets set again
 174  * asynchronously, this will be called again before we return to
 175  * user mode.
 176  *
 177  * Called without locks.
 178  */
 179 static inline void tracehook_notify_resume(struct pt_regs *regs)
 180 {
 181         /*
 182          * The caller just cleared TIF_NOTIFY_RESUME. This barrier
 183          * pairs with task_work_add()->set_notify_resume() after
 184          * hlist_add_head(task->task_works);
 185          */
 186         smp_mb__after_atomic();
 187         if (unlikely(current->task_works))
 188                 task_work_run();
 189
 190         mem_cgroup_handle_over_high();
 191         blkcg_maybe_throttle_current();
 192 }
 193
 194 #endif  /* <linux/tracehook.h> */