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 %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 */
101 static inline __must_check int tracehook_report_syscall_entry(
102 struct pt_regs *regs)
103 {
104 return ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_ENTRY);
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 */
124 static 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, PTRACE_EVENTMSG_SYSCALL_EXIT);
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 */
143 static 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 */
158 static 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 */
179 static 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 #ifdef CONFIG_KEYS_REQUEST_CACHE
191 if (unlikely(current->cached_requested_key)) {
192 key_put(current->cached_requested_key);
193 current->cached_requested_key = NULL;
194 }
195 #endif
196
197 mem_cgroup_handle_over_high();
198 blkcg_maybe_throttle_current();
199 }
200
201 #endif /* <linux/tracehook.h> */