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>
53 #include <linux/memcontrol.h>
54 #include <linux/blk-cgroup.h>
55 struct linux_binprm;
56 
57 /*
58  * ptrace report for syscall entry and exit looks identical.
59  */
ptrace_report_syscall(struct pt_regs * regs)60 static inline int ptrace_report_syscall(struct pt_regs *regs)
61 {
62 	int ptrace = current->ptrace;
63 
64 	if (!(ptrace & PT_PTRACED))
65 		return 0;
66 
67 	ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
68 
69 	/*
70 	 * this isn't the same as continuing with a signal, but it will do
71 	 * for normal use.  strace only continues with a signal if the
72 	 * stopping signal is not SIGTRAP.  -brl
73 	 */
74 	if (current->exit_code) {
75 		send_sig(current->exit_code, current, 1);
76 		current->exit_code = 0;
77 	}
78 
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 has been set, when the
87  * 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  */
tracehook_report_syscall_entry(struct pt_regs * regs)101 static inline __must_check int tracehook_report_syscall_entry(
102 	struct pt_regs *regs)
103 {
104 	return ptrace_report_syscall(regs);
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  */
tracehook_report_syscall_exit(struct pt_regs * regs,int step)124 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
125 {
126 	if (step) {
127 		siginfo_t info;
128 		clear_siginfo(&info);
129 		user_single_step_siginfo(current, regs, &info);
130 		force_sig_info(SIGTRAP, &info, current);
131 		return;
132 	}
133 
134 	ptrace_report_syscall(regs);
135 }
136 
137 /**
138  * tracehook_signal_handler - signal handler setup is complete
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 stepping)148 static inline void tracehook_signal_handler(int stepping)
149 {
150 	if (stepping)
151 		ptrace_notify(SIGTRAP);
152 }
153 
154 /**
155  * set_notify_resume - cause tracehook_notify_resume() to be called
156  * @task:		task that will call tracehook_notify_resume()
157  *
158  * Calling this arranges that @task will call tracehook_notify_resume()
159  * before returning to user mode.  If it's already running in user mode,
160  * it will enter the kernel and call tracehook_notify_resume() soon.
161  * If it's blocked, it will not be woken.
162  */
set_notify_resume(struct task_struct * task)163 static inline void set_notify_resume(struct task_struct *task)
164 {
165 #ifdef TIF_NOTIFY_RESUME
166 	if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
167 		kick_process(task);
168 #endif
169 }
170 
171 /**
172  * tracehook_notify_resume - report when about to return to user mode
173  * @regs:		user-mode registers of @current task
174  *
175  * This is called when %TIF_NOTIFY_RESUME has been set.  Now we are
176  * about to return to user mode, and the user state in @regs can be
177  * inspected or adjusted.  The caller in arch code has cleared
178  * %TIF_NOTIFY_RESUME before the call.  If the flag gets set again
179  * asynchronously, this will be called again before we return to
180  * user mode.
181  *
182  * Called without locks.
183  */
tracehook_notify_resume(struct pt_regs * regs)184 static inline void tracehook_notify_resume(struct pt_regs *regs)
185 {
186 	/*
187 	 * The caller just cleared TIF_NOTIFY_RESUME. This barrier
188 	 * pairs with task_work_add()->set_notify_resume() after
189 	 * hlist_add_head(task->task_works);
190 	 */
191 	smp_mb__after_atomic();
192 	if (unlikely(current->task_works))
193 		task_work_run();
194 
195 	mem_cgroup_handle_over_high();
196 	blkcg_maybe_throttle_current();
197 }
198 
199 #endif	/* <linux/tracehook.h> */
200