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