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> 55struct linux_binprm; 56 57/* 58 * ptrace report for syscall entry and exit looks identical. 59 */ 60static 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 */ 101static 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 */ 124static 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 */ 143static 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 */ 158static 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 */ 179static 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> */ 195