include/linux/tracehook.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Tracing hooks
   4  *
   5  * Copyright (C) 2008-2009 Red Hat, Inc.  All rights reserved.
   6  *
   7  * This file defines hook entry points called by core code where
   8  * user tracing/debugging support might need to do something.  These
   9  * entry points are called tracehook_*().  Each hook declared below
  10  * has a detailed kerneldoc comment giving the context (locking et
  11  * al) from which it is called, and the meaning of its return value.
  12  *
  13  * Each function here typically has only one call site, so it is ok
  14  * to have some nontrivial tracehook_*() inlines.  In all cases, the
  15  * fast path when no tracing is enabled should be very short.
  16  *
  17  * The purpose of this file and the tracehook_* layer is to consolidate
  18  * the interface that the kernel core and arch code uses to enable any
  19  * user debugging or tracing facility (such as ptrace).  The interfaces
  20  * here are carefully documented so that maintainers of core and arch
  21  * code do not need to think about the implementation details of the
  22  * tracing facilities.  Likewise, maintainers of the tracing code do not
  23  * need to understand all the calling core or arch code in detail, just
  24  * documented circumstances of each call, such as locking conditions.
  25  *
  26  * If the calling core code changes so that locking is different, then
  27  * it is ok to change the interface documented here.  The maintainer of
  28  * core code changing should notify the maintainers of the tracing code
  29  * that they need to work out the change.
  30  *
  31  * Some tracehook_*() inlines take arguments that the current tracing
  32  * implementations might not necessarily use.  These function signatures
  33  * are chosen to pass in all the information that is on hand in the
  34  * caller and might conceivably be relevant to a tracer, so that the
  35  * core code won't have to be updated when tracing adds more features.
  36  * If a call site changes so that some of those parameters are no longer
  37  * already on hand without extra work, then the tracehook_* interface
  38  * can change so there is no make-work burden on the core code.  The
  39  * maintainer of core code changing should notify the maintainers of the
  40  * tracing code that they need to work out the change.
  41  */
  42
  43 #ifndef _LINUX_TRACEHOOK_H
  44 #define _LINUX_TRACEHOOK_H      1
  45
  46 #include <linux/sched.h>
  47 #include <linux/ptrace.h>
  48 #include <linux/security.h>
  49 #include <linux/task_work.h>
  50 #include <linux/memcontrol.h>
  51 #include <linux/blk-cgroup.h>
  52 struct linux_binprm;
  53
  54 /*
  55  * ptrace report for syscall entry and exit looks identical.
  56  */
  57 static inline int ptrace_report_syscall(struct pt_regs *regs,
  58                                         unsigned long message)
  59 {
  60         int ptrace = current->ptrace;
  61
  62         if (!(ptrace & PT_PTRACED))
  63                 return 0;
  64
  65         current->ptrace_message = message;
  66         ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
  67
  68         /*
  69          * this isn't the same as continuing with a signal, but it will do
  70          * for normal use.  strace only continues with a signal if the
  71          * stopping signal is not SIGTRAP.  -brl
  72          */
  73         if (current->exit_code) {
  74                 send_sig(current->exit_code, current, 1);
  75                 current->exit_code = 0;
  76         }
  77
  78         current->ptrace_message = 0;
  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 %SYSCALL_WORK_SYSCALL_TRACE or
  87  * %SYSCALL_WORK_SYSCALL_EMU have been set, when the current task has just
  88  * entered the kernel for a system call.  Full user register state is
  89  * available here.  Changing the values in @regs can affect the system
  90  * call number and arguments to be tried.  It is safe to block here,
  91  * preventing the system call from beginning.
  92  *
  93  * Returns zero normally, or nonzero if the calling arch code should abort
  94  * the system call.  That must prevent normal entry so no system call is
  95  * made.  If @task ever returns to user mode after this, its register state
  96  * is unspecified, but should be something harmless like an %ENOSYS error
  97  * return.  It should preserve enough information so that syscall_rollback()
  98  * can work (see asm-generic/syscall.h).
  99  *
 100  * Called without locks, just after entering kernel mode.
 101  */
 102 static inline __must_check int tracehook_report_syscall_entry(
 103         struct pt_regs *regs)
 104 {
 105         return ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_ENTRY);
 106 }
 107
 108 /**
 109  * tracehook_report_syscall_exit - task has just finished a system call
 110  * @regs:               user register state of current task
 111  * @step:               nonzero if simulating single-step or block-step
 112  *
 113  * This will be called if %SYSCALL_WORK_SYSCALL_TRACE has been set, when
 114  * the current task has just finished an attempted system call.  Full
 115  * user register state is available here.  It is safe to block here,
 116  * preventing signals from being processed.
 117  *
 118  * If @step is nonzero, this report is also in lieu of the normal
 119  * trap that would follow the system call instruction because
 120  * user_enable_block_step() or user_enable_single_step() was used.
 121  * In this case, %SYSCALL_WORK_SYSCALL_TRACE might not be set.
 122  *
 123  * Called without locks, just before checking for pending signals.
 124  */
 125 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
 126 {
 127         if (step)
 128                 user_single_step_report(regs);
 129         else
 130                 ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_EXIT);
 131 }
 132
 133 /**
 134  * tracehook_signal_handler - signal handler setup is complete
 135  * @stepping:           nonzero if debugger single-step or block-step in use
 136  *
 137  * Called by the arch code after a signal handler has been set up.
 138  * Register and stack state reflects the user handler about to run.
 139  * Signal mask changes have already been made.
 140  *
 141  * Called without locks, shortly before returning to user mode
 142  * (or handling more signals).
 143  */
 144 static inline void tracehook_signal_handler(int stepping)
 145 {
 146         if (stepping)
 147                 ptrace_notify(SIGTRAP);
 148 }
 149
 150 /**
 151  * set_notify_resume - cause tracehook_notify_resume() to be called
 152  * @task:               task that will call tracehook_notify_resume()
 153  *
 154  * Calling this arranges that @task will call tracehook_notify_resume()
 155  * before returning to user mode.  If it's already running in user mode,
 156  * it will enter the kernel and call tracehook_notify_resume() soon.
 157  * If it's blocked, it will not be woken.
 158  */
 159 static inline void set_notify_resume(struct task_struct *task)
 160 {
 161 #ifdef TIF_NOTIFY_RESUME
 162         if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
 163                 kick_process(task);
 164 #endif
 165 }
 166
 167 /**
 168  * tracehook_notify_resume - report when about to return to user mode
 169  * @regs:               user-mode registers of @current task
 170  *
 171  * This is called when %TIF_NOTIFY_RESUME has been set.  Now we are
 172  * about to return to user mode, and the user state in @regs can be
 173  * inspected or adjusted.  The caller in arch code has cleared
 174  * %TIF_NOTIFY_RESUME before the call.  If the flag gets set again
 175  * asynchronously, this will be called again before we return to
 176  * user mode.
 177  *
 178  * Called without locks.
 179  */
 180 static inline void tracehook_notify_resume(struct pt_regs *regs)
 181 {
 182         clear_thread_flag(TIF_NOTIFY_RESUME);
 183         /*
 184          * This barrier pairs with task_work_add()->set_notify_resume() after
 185          * hlist_add_head(task->task_works);
 186          */
 187         smp_mb__after_atomic();
 188         if (unlikely(current->task_works))
 189                 task_work_run();
 190
 191 #ifdef CONFIG_KEYS_REQUEST_CACHE
 192         if (unlikely(current->cached_requested_key)) {
 193                 key_put(current->cached_requested_key);
 194                 current->cached_requested_key = NULL;
 195         }
 196 #endif
 197
 198         mem_cgroup_handle_over_high();
 199         blkcg_maybe_throttle_current();
 200
 201         rseq_handle_notify_resume(NULL, regs);
 202 }
 203
 204 /*
 205  * called by exit_to_user_mode_loop() if ti_work & _TIF_NOTIFY_SIGNAL. This
 206  * is currently used by TWA_SIGNAL based task_work, which requires breaking
 207  * wait loops to ensure that task_work is noticed and run.
 208  */
 209 static inline void tracehook_notify_signal(void)
 210 {
 211         clear_thread_flag(TIF_NOTIFY_SIGNAL);
 212         smp_mb__after_atomic();
 213         if (current->task_works)
 214                 task_work_run();
 215 }
 216
 217 /*
 218  * Called when we have work to process from exit_to_user_mode_loop()
 219  */
 220 static inline void set_notify_signal(struct task_struct *task)
 221 {
 222         if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_SIGNAL) &&
 223             !wake_up_state(task, TASK_INTERRUPTIBLE))
 224                 kick_process(task);
 225 }
 226
 227 #endif  /* <linux/tracehook.h> */