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 struct linux_binprm;
53
54 /*
55 * ptrace report for syscall entry and exit looks identical.
56 */
ptrace_report_syscall(struct pt_regs * regs)57 static 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 has been set, when the
84 * 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 */
tracehook_report_syscall_entry(struct pt_regs * regs)98 static 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 */
tracehook_report_syscall_exit(struct pt_regs * regs,int step)121 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
122 {
123 if (step) {
124 siginfo_t info;
125 user_single_step_siginfo(current, regs, &info);
126 force_sig_info(SIGTRAP, &info, current);
127 return;
128 }
129
130 ptrace_report_syscall(regs);
131 }
132
133 /**
134 * tracehook_signal_handler - signal handler setup is complete
135 * @sig: number of signal being delivered
136 * @info: siginfo_t of signal being delivered
137 * @ka: sigaction setting that chose the handler
138 * @regs: user register state
139 * @stepping: nonzero if debugger single-step or block-step in use
140 *
141 * Called by the arch code after a signal handler has been set up.
142 * Register and stack state reflects the user handler about to run.
143 * Signal mask changes have already been made.
144 *
145 * Called without locks, shortly before returning to user mode
146 * (or handling more signals).
147 */
tracehook_signal_handler(int sig,siginfo_t * info,const struct k_sigaction * ka,struct pt_regs * regs,int stepping)148 static inline void tracehook_signal_handler(int sig, siginfo_t *info,
149 const struct k_sigaction *ka,
150 struct pt_regs *regs, int stepping)
151 {
152 if (stepping)
153 ptrace_notify(SIGTRAP);
154 }
155
156 #ifdef TIF_NOTIFY_RESUME
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 */
set_notify_resume(struct task_struct * task)166 static inline void set_notify_resume(struct task_struct *task)
167 {
168 if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
169 kick_process(task);
170 }
171
172 /**
173 * tracehook_notify_resume - report when about to return to user mode
174 * @regs: user-mode registers of @current task
175 *
176 * This is called when %TIF_NOTIFY_RESUME has been set. Now we are
177 * about to return to user mode, and the user state in @regs can be
178 * inspected or adjusted. The caller in arch code has cleared
179 * %TIF_NOTIFY_RESUME before the call. If the flag gets set again
180 * asynchronously, this will be called again before we return to
181 * user mode.
182 *
183 * Called without locks.
184 */
tracehook_notify_resume(struct pt_regs * regs)185 static inline void tracehook_notify_resume(struct pt_regs *regs)
186 {
187 }
188 #endif /* TIF_NOTIFY_RESUME */
189
190 #endif /* <linux/tracehook.h> */
191