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> 53struct linux_binprm; 54 55/* 56 * ptrace report for syscall entry and exit looks identical. 57 */ 58static 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 */ 99static 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 */ 122static 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 */ 149static 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 */ 166static 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 */ 187static 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> */ 200