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> 52struct linux_binprm; 53 54/* 55 * ptrace report for syscall entry and exit looks identical. 56 */ 57static inline int ptrace_report_syscall(struct pt_regs *regs) 58{ 59 int ptrace = current->ptrace; 60 61 if (!(ptrace & PT_PTRACED)) 62 return 0; 63 64 ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0)); 65 66 /* 67 * this isn't the same as continuing with a signal, but it will do 68 * for normal use. strace only continues with a signal if the 69 * stopping signal is not SIGTRAP. -brl 70 */ 71 if (current->exit_code) { 72 send_sig(current->exit_code, current, 1); 73 current->exit_code = 0; 74 } 75 76 return fatal_signal_pending(current); 77} 78 79/** 80 * tracehook_report_syscall_entry - task is about to attempt a system call 81 * @regs: user register state of current task 82 * 83 * This will be called if %TIF_SYSCALL_TRACE or %TIF_SYSCALL_EMU have been set, 84 * when the current task has just entered the kernel for a system call. 85 * Full user register state is available here. Changing the values 86 * in @regs can affect the system call number and arguments to be tried. 87 * It is safe to block here, preventing the system call from beginning. 88 * 89 * Returns zero normally, or nonzero if the calling arch code should abort 90 * the system call. That must prevent normal entry so no system call is 91 * made. If @task ever returns to user mode after this, its register state 92 * is unspecified, but should be something harmless like an %ENOSYS error 93 * return. It should preserve enough information so that syscall_rollback() 94 * can work (see asm-generic/syscall.h). 95 * 96 * Called without locks, just after entering kernel mode. 97 */ 98static inline __must_check int tracehook_report_syscall_entry( 99 struct pt_regs *regs) 100{ 101 return ptrace_report_syscall(regs); 102} 103 104/** 105 * tracehook_report_syscall_exit - task has just finished a system call 106 * @regs: user register state of current task 107 * @step: nonzero if simulating single-step or block-step 108 * 109 * This will be called if %TIF_SYSCALL_TRACE has been set, when the 110 * current task has just finished an attempted system call. Full 111 * user register state is available here. It is safe to block here, 112 * preventing signals from being processed. 113 * 114 * If @step is nonzero, this report is also in lieu of the normal 115 * trap that would follow the system call instruction because 116 * user_enable_block_step() or user_enable_single_step() was used. 117 * In this case, %TIF_SYSCALL_TRACE might not be set. 118 * 119 * Called without locks, just before checking for pending signals. 120 */ 121static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step) 122{ 123 if (step) 124 user_single_step_report(regs); 125 else 126 ptrace_report_syscall(regs); 127} 128 129/** 130 * tracehook_signal_handler - signal handler setup is complete 131 * @stepping: nonzero if debugger single-step or block-step in use 132 * 133 * Called by the arch code after a signal handler has been set up. 134 * Register and stack state reflects the user handler about to run. 135 * Signal mask changes have already been made. 136 * 137 * Called without locks, shortly before returning to user mode 138 * (or handling more signals). 139 */ 140static inline void tracehook_signal_handler(int stepping) 141{ 142 if (stepping) 143 ptrace_notify(SIGTRAP); 144} 145 146/** 147 * set_notify_resume - cause tracehook_notify_resume() to be called 148 * @task: task that will call tracehook_notify_resume() 149 * 150 * Calling this arranges that @task will call tracehook_notify_resume() 151 * before returning to user mode. If it's already running in user mode, 152 * it will enter the kernel and call tracehook_notify_resume() soon. 153 * If it's blocked, it will not be woken. 154 */ 155static inline void set_notify_resume(struct task_struct *task) 156{ 157#ifdef TIF_NOTIFY_RESUME 158 if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME)) 159 kick_process(task); 160#endif 161} 162 163/** 164 * tracehook_notify_resume - report when about to return to user mode 165 * @regs: user-mode registers of @current task 166 * 167 * This is called when %TIF_NOTIFY_RESUME has been set. Now we are 168 * about to return to user mode, and the user state in @regs can be 169 * inspected or adjusted. The caller in arch code has cleared 170 * %TIF_NOTIFY_RESUME before the call. If the flag gets set again 171 * asynchronously, this will be called again before we return to 172 * user mode. 173 * 174 * Called without locks. 175 */ 176static inline void tracehook_notify_resume(struct pt_regs *regs) 177{ 178 /* 179 * The caller just cleared TIF_NOTIFY_RESUME. This barrier 180 * pairs with task_work_add()->set_notify_resume() after 181 * hlist_add_head(task->task_works); 182 */ 183 smp_mb__after_atomic(); 184 if (unlikely(current->task_works)) 185 task_work_run(); 186 187 mem_cgroup_handle_over_high(); 188 blkcg_maybe_throttle_current(); 189} 190 191#endif /* <linux/tracehook.h> */ 192