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 struct linux_binprm;
  54
  55 /*
  56  * ptrace report for syscall entry and exit looks identical.
  57  */
  58 static 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  */
  99 static 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  */
 122 static 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  */
 149 static 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  */
 166 static 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  */
 187 static 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> */