xref: /freebsd/sys/kern/subr_syscall.c (revision fdc418f15e92732a3551832bcb625ba9b47242df)
1 /*-
2  * SPDX-License-Identifier: BSD-4-Clause
3  *
4  * Copyright (C) 1994, David Greenman
5  * Copyright (c) 1990, 1993
6  *	The Regents of the University of California.  All rights reserved.
7  * Copyright (C) 2010 Konstantin Belousov <kib@freebsd.org>
8  *
9  * This code is derived from software contributed to Berkeley by
10  * the University of Utah, and William Jolitz.
11  *
12  * Redistribution and use in source and binary forms, with or without
13  * modification, are permitted provided that the following conditions
14  * are met:
15  * 1. Redistributions of source code must retain the above copyright
16  *    notice, this list of conditions and the following disclaimer.
17  * 2. Redistributions in binary form must reproduce the above copyright
18  *    notice, this list of conditions and the following disclaimer in the
19  *    documentation and/or other materials provided with the distribution.
20  * 3. All advertising materials mentioning features or use of this software
21  *    must display the following acknowledgement:
22  *	This product includes software developed by the University of
23  *	California, Berkeley and its contributors.
24  * 4. Neither the name of the University nor the names of its contributors
25  *    may be used to endorse or promote products derived from this software
26  *    without specific prior written permission.
27  *
28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38  * SUCH DAMAGE.
39  *
40  *	from: @(#)trap.c	7.4 (Berkeley) 5/13/91
41  */
42 
43 #include "opt_capsicum.h"
44 #include "opt_ktrace.h"
45 
46 __FBSDID("$FreeBSD$");
47 
48 #include <sys/capsicum.h>
49 #include <sys/ktr.h>
50 #include <sys/vmmeter.h>
51 #ifdef KTRACE
52 #include <sys/uio.h>
53 #include <sys/ktrace.h>
54 #endif
55 #include <security/audit/audit.h>
56 
57 static inline void
58 syscallenter(struct thread *td)
59 {
60 	struct proc *p;
61 	struct syscall_args *sa;
62 	struct sysent *se;
63 	int error, traced;
64 	bool sy_thr_static;
65 
66 	VM_CNT_INC(v_syscall);
67 	p = td->td_proc;
68 	sa = &td->td_sa;
69 
70 	td->td_pticks = 0;
71 	if (__predict_false(td->td_cowgen != atomic_load_int(&p->p_cowgen)))
72 		thread_cow_update(td);
73 	traced = (p->p_flag & P_TRACED) != 0;
74 	if (__predict_false(traced || td->td_dbgflags & TDB_USERWR)) {
75 		PROC_LOCK(p);
76 		td->td_dbgflags &= ~TDB_USERWR;
77 		if (traced)
78 			td->td_dbgflags |= TDB_SCE;
79 		PROC_UNLOCK(p);
80 	}
81 	error = (p->p_sysent->sv_fetch_syscall_args)(td);
82 	se = sa->callp;
83 #ifdef KTRACE
84 	if (KTRPOINT(td, KTR_SYSCALL))
85 		ktrsyscall(sa->code, se->sy_narg, sa->args);
86 #endif
87 	KTR_START4(KTR_SYSC, "syscall", syscallname(p, sa->code),
88 	    (uintptr_t)td, "pid:%d", td->td_proc->p_pid, "arg0:%p", sa->args[0],
89 	    "arg1:%p", sa->args[1], "arg2:%p", sa->args[2]);
90 
91 	if (__predict_false(error != 0)) {
92 		td->td_errno = error;
93 		goto retval;
94 	}
95 
96 	if (__predict_false(traced)) {
97 		PROC_LOCK(p);
98 		if (p->p_ptevents & PTRACE_SCE)
99 			ptracestop((td), SIGTRAP, NULL);
100 		PROC_UNLOCK(p);
101 
102 		if ((td->td_dbgflags & TDB_USERWR) != 0) {
103 			/*
104 			 * Reread syscall number and arguments if debugger
105 			 * modified registers or memory.
106 			 */
107 			error = (p->p_sysent->sv_fetch_syscall_args)(td);
108 			se = sa->callp;
109 #ifdef KTRACE
110 			if (KTRPOINT(td, KTR_SYSCALL))
111 				ktrsyscall(sa->code, se->sy_narg, sa->args);
112 #endif
113 			if (error != 0) {
114 				td->td_errno = error;
115 				goto retval;
116 			}
117 		}
118 	}
119 
120 #ifdef CAPABILITY_MODE
121 	/*
122 	 * In capability mode, we only allow access to system calls
123 	 * flagged with SYF_CAPENABLED.
124 	 */
125 	if (__predict_false(IN_CAPABILITY_MODE(td) &&
126 	    (se->sy_flags & SYF_CAPENABLED) == 0)) {
127 		td->td_errno = error = ECAPMODE;
128 		goto retval;
129 	}
130 #endif
131 
132 	/*
133 	 * Fetch fast sigblock value at the time of syscall entry to
134 	 * handle sleepqueue primitives which might call cursig().
135 	 */
136 	if (__predict_false(sigfastblock_fetch_always))
137 		(void)sigfastblock_fetch(td);
138 
139 	/* Let system calls set td_errno directly. */
140 	KASSERT((td->td_pflags & TDP_NERRNO) == 0,
141 	    ("%s: TDP_NERRNO set", __func__));
142 
143 	sy_thr_static = (se->sy_thrcnt & SY_THR_STATIC) != 0;
144 
145 	if (__predict_false(SYSTRACE_ENABLED() ||
146 	    AUDIT_SYSCALL_ENTER(sa->code, td) ||
147 	    !sy_thr_static)) {
148 		if (!sy_thr_static) {
149 			error = syscall_thread_enter(td, se);
150 			if (error != 0) {
151 				td->td_errno = error;
152 				goto retval;
153 			}
154 		}
155 
156 #ifdef KDTRACE_HOOKS
157 		/* Give the syscall:::entry DTrace probe a chance to fire. */
158 		if (__predict_false(se->sy_entry != 0))
159 			(*systrace_probe_func)(sa, SYSTRACE_ENTRY, 0);
160 #endif
161 		error = (se->sy_call)(td, sa->args);
162 		/* Save the latest error return value. */
163 		if (__predict_false((td->td_pflags & TDP_NERRNO) != 0))
164 			td->td_pflags &= ~TDP_NERRNO;
165 		else
166 			td->td_errno = error;
167 
168 		/*
169 		 * Note that some syscall implementations (e.g., sys_execve)
170 		 * will commit the audit record just before their final return.
171 		 * These were done under the assumption that nothing of interest
172 		 * would happen between their return and here, where we would
173 		 * normally commit the audit record.  These assumptions will
174 		 * need to be revisited should any substantial logic be added
175 		 * above.
176 		 */
177 		AUDIT_SYSCALL_EXIT(error, td);
178 
179 #ifdef KDTRACE_HOOKS
180 		/* Give the syscall:::return DTrace probe a chance to fire. */
181 		if (__predict_false(se->sy_return != 0))
182 			(*systrace_probe_func)(sa, SYSTRACE_RETURN,
183 			    error ? -1 : td->td_retval[0]);
184 #endif
185 
186 		if (!sy_thr_static)
187 			syscall_thread_exit(td, se);
188 	} else {
189 		error = (se->sy_call)(td, sa->args);
190 		/* Save the latest error return value. */
191 		if (__predict_false((td->td_pflags & TDP_NERRNO) != 0))
192 			td->td_pflags &= ~TDP_NERRNO;
193 		else
194 			td->td_errno = error;
195 	}
196 
197  retval:
198 	KTR_STOP4(KTR_SYSC, "syscall", syscallname(p, sa->code),
199 	    (uintptr_t)td, "pid:%d", td->td_proc->p_pid, "error:%d", error,
200 	    "retval0:%#lx", td->td_retval[0], "retval1:%#lx",
201 	    td->td_retval[1]);
202 	if (__predict_false(traced)) {
203 		PROC_LOCK(p);
204 		td->td_dbgflags &= ~TDB_SCE;
205 		PROC_UNLOCK(p);
206 	}
207 	(p->p_sysent->sv_set_syscall_retval)(td, error);
208 }
209 
210 static inline void
211 syscallret(struct thread *td)
212 {
213 	struct proc *p;
214 	struct syscall_args *sa;
215 	ksiginfo_t ksi;
216 	int traced;
217 
218 	KASSERT(td->td_errno != ERELOOKUP,
219 	    ("ERELOOKUP not consumed syscall %d", td->td_sa.code));
220 
221 	p = td->td_proc;
222 	sa = &td->td_sa;
223 	if (__predict_false(td->td_errno == ENOTCAPABLE ||
224 	    td->td_errno == ECAPMODE)) {
225 		if ((trap_enotcap ||
226 		    (p->p_flag2 & P2_TRAPCAP) != 0) && IN_CAPABILITY_MODE(td)) {
227 			ksiginfo_init_trap(&ksi);
228 			ksi.ksi_signo = SIGTRAP;
229 			ksi.ksi_errno = td->td_errno;
230 			ksi.ksi_code = TRAP_CAP;
231 			ksi.ksi_info.si_syscall = sa->original_code;
232 			trapsignal(td, &ksi);
233 		}
234 	}
235 
236 	/*
237 	 * Handle reschedule and other end-of-syscall issues
238 	 */
239 	userret(td, td->td_frame);
240 
241 #ifdef KTRACE
242 	if (KTRPOINT(td, KTR_SYSRET)) {
243 		ktrsysret(sa->code, td->td_errno, td->td_retval[0]);
244 	}
245 #endif
246 
247 	traced = 0;
248 	if (__predict_false(p->p_flag & P_TRACED)) {
249 		traced = 1;
250 		PROC_LOCK(p);
251 		td->td_dbgflags |= TDB_SCX;
252 		PROC_UNLOCK(p);
253 	}
254 	if (__predict_false(traced ||
255 	    (td->td_dbgflags & (TDB_EXEC | TDB_FORK)) != 0)) {
256 		PROC_LOCK(p);
257 		/*
258 		 * Linux debuggers expect an additional stop for exec,
259 		 * between the usual syscall entry and exit.  Raise
260 		 * the exec event now and then clear TDB_EXEC so that
261 		 * the next stop is reported as a syscall exit by
262 		 * linux_ptrace_status().
263 		 *
264 		 * We are accessing p->p_pptr without any additional
265 		 * locks here: it cannot change while p is kept locked;
266 		 * while the debugger could in theory change its ABI
267 		 * while tracing another process, the outcome of such
268 		 * a race wouln't be deterministic anyway.
269 		 */
270 		if (traced && (td->td_dbgflags & TDB_EXEC) != 0 &&
271 		    SV_PROC_ABI(p->p_pptr) == SV_ABI_LINUX) {
272 			ptracestop(td, SIGTRAP, NULL);
273 			td->td_dbgflags &= ~TDB_EXEC;
274 		}
275 		/*
276 		 * If tracing the execed process, trap to the debugger
277 		 * so that breakpoints can be set before the program
278 		 * executes.  If debugger requested tracing of syscall
279 		 * returns, do it now too.
280 		 */
281 		if (traced &&
282 		    ((td->td_dbgflags & (TDB_FORK | TDB_EXEC)) != 0 ||
283 		    (p->p_ptevents & PTRACE_SCX) != 0))
284 			ptracestop(td, SIGTRAP, NULL);
285 		td->td_dbgflags &= ~(TDB_SCX | TDB_EXEC | TDB_FORK);
286 		PROC_UNLOCK(p);
287 	}
288 }
289