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1/*
2 * Seccomp filter example for x86 (32-bit and 64-bit) with BPF macros
3 *
4 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
5 * Author: Will Drewry <wad@chromium.org>
6 *
7 * The code may be used by anyone for any purpose,
8 * and can serve as a starting point for developing
9 * applications using prctl(PR_SET_SECCOMP, 2, ...).
10 */
11#if defined(__i386__) || defined(__x86_64__)
12#define SUPPORTED_ARCH 1
13#endif
14
15#if defined(SUPPORTED_ARCH)
16#define __USE_GNU 1
17#define _GNU_SOURCE 1
18
19#include <linux/types.h>
20#include <linux/filter.h>
21#include <linux/seccomp.h>
22#include <linux/unistd.h>
23#include <signal.h>
24#include <stdio.h>
25#include <stddef.h>
26#include <string.h>
27#include <sys/prctl.h>
28#include <unistd.h>
29
30#define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
31#define syscall_nr (offsetof(struct seccomp_data, nr))
32
33#if defined(__i386__)
34#define REG_RESULT REG_EAX
35#define REG_SYSCALL REG_EAX
36#define REG_ARG0 REG_EBX
37#define REG_ARG1 REG_ECX
38#define REG_ARG2 REG_EDX
39#define REG_ARG3 REG_ESI
40#define REG_ARG4 REG_EDI
41#define REG_ARG5 REG_EBP
42#elif defined(__x86_64__)
43#define REG_RESULT REG_RAX
44#define REG_SYSCALL REG_RAX
45#define REG_ARG0 REG_RDI
46#define REG_ARG1 REG_RSI
47#define REG_ARG2 REG_RDX
48#define REG_ARG3 REG_R10
49#define REG_ARG4 REG_R8
50#define REG_ARG5 REG_R9
51#endif
52
53#ifndef PR_SET_NO_NEW_PRIVS
54#define PR_SET_NO_NEW_PRIVS 38
55#endif
56
57#ifndef SYS_SECCOMP
58#define SYS_SECCOMP 1
59#endif
60
61static void emulator(int nr, siginfo_t *info, void *void_context)
62{
63 ucontext_t *ctx = (ucontext_t *)(void_context);
64 int syscall;
65 char *buf;
66 ssize_t bytes;
67 size_t len;
68 if (info->si_code != SYS_SECCOMP)
69 return;
70 if (!ctx)
71 return;
72 syscall = ctx->uc_mcontext.gregs[REG_SYSCALL];
73 buf = (char *) ctx->uc_mcontext.gregs[REG_ARG1];
74 len = (size_t) ctx->uc_mcontext.gregs[REG_ARG2];
75
76 if (syscall != __NR_write)
77 return;
78 if (ctx->uc_mcontext.gregs[REG_ARG0] != STDERR_FILENO)
79 return;
80 /* Redirect stderr messages to stdout. Doesn't handle EINTR, etc */
81 ctx->uc_mcontext.gregs[REG_RESULT] = -1;
82 if (write(STDOUT_FILENO, "[ERR] ", 6) > 0) {
83 bytes = write(STDOUT_FILENO, buf, len);
84 ctx->uc_mcontext.gregs[REG_RESULT] = bytes;
85 }
86 return;
87}
88
89static int install_emulator(void)
90{
91 struct sigaction act;
92 sigset_t mask;
93 memset(&act, 0, sizeof(act));
94 sigemptyset(&mask);
95 sigaddset(&mask, SIGSYS);
96
97 act.sa_sigaction = &emulator;
98 act.sa_flags = SA_SIGINFO;
99 if (sigaction(SIGSYS, &act, NULL) < 0) {
100 perror("sigaction");
101 return -1;
102 }
103 if (sigprocmask(SIG_UNBLOCK, &mask, NULL)) {
104 perror("sigprocmask");
105 return -1;
106 }
107 return 0;
108}
109
110static int install_filter(void)
111{
112 struct sock_filter filter[] = {
113 /* Grab the system call number */
114 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_nr),
115 /* Jump table for the allowed syscalls */
116 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 0, 1),
117 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
118#ifdef __NR_sigreturn
119 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 0, 1),
120 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
121#endif
122 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 0, 1),
123 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
124 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 0, 1),
125 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
126 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0),
127 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 3, 2),
128
129 /* Check that read is only using stdin. */
130 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
131 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 4, 0),
132 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
133
134 /* Check that write is only using stdout */
135 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
136 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0),
137 /* Trap attempts to write to stderr */
138 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 1, 2),
139
140 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
141 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP),
142 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
143 };
144 struct sock_fprog prog = {
145 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
146 .filter = filter,
147 };
148
149 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
150 perror("prctl(NO_NEW_PRIVS)");
151 return 1;
152 }
153
154
155 if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
156 perror("prctl");
157 return 1;
158 }
159 return 0;
160}
161
162#define payload(_c) (_c), sizeof((_c))
163int main(int argc, char **argv)
164{
165 char buf[4096];
166 ssize_t bytes = 0;
167 if (install_emulator())
168 return 1;
169 if (install_filter())
170 return 1;
171 syscall(__NR_write, STDOUT_FILENO,
172 payload("OHAI! WHAT IS YOUR NAME? "));
173 bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf));
174 syscall(__NR_write, STDOUT_FILENO, payload("HELLO, "));
175 syscall(__NR_write, STDOUT_FILENO, buf, bytes);
176 syscall(__NR_write, STDERR_FILENO,
177 payload("Error message going to STDERR\n"));
178 return 0;
179}
180#else /* SUPPORTED_ARCH */
181/*
182 * This sample is x86-only. Since kernel samples are compiled with the
183 * host toolchain, a non-x86 host will result in using only the main()
184 * below.
185 */
186int main(void)
187{
188 return 1;
189}
190#endif /* SUPPORTED_ARCH */
1/*
2 * Seccomp filter example for x86 (32-bit and 64-bit) with BPF macros
3 *
4 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
5 * Author: Will Drewry <wad@chromium.org>
6 *
7 * The code may be used by anyone for any purpose,
8 * and can serve as a starting point for developing
9 * applications using prctl(PR_SET_SECCOMP, 2, ...).
10 */
11#if defined(__i386__) || defined(__x86_64__)
12#define SUPPORTED_ARCH 1
13#endif
14
15#if defined(SUPPORTED_ARCH)
16#define __USE_GNU 1
17#define _GNU_SOURCE 1
18
19#include <linux/types.h>
20#include <linux/filter.h>
21#include <linux/seccomp.h>
22#include <linux/unistd.h>
23#include <signal.h>
24#include <stdio.h>
25#include <stddef.h>
26#include <string.h>
27#include <sys/prctl.h>
28#include <unistd.h>
29
30#define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
31#define syscall_nr (offsetof(struct seccomp_data, nr))
32
33#if defined(__i386__)
34#define REG_RESULT REG_EAX
35#define REG_SYSCALL REG_EAX
36#define REG_ARG0 REG_EBX
37#define REG_ARG1 REG_ECX
38#define REG_ARG2 REG_EDX
39#define REG_ARG3 REG_ESI
40#define REG_ARG4 REG_EDI
41#define REG_ARG5 REG_EBP
42#elif defined(__x86_64__)
43#define REG_RESULT REG_RAX
44#define REG_SYSCALL REG_RAX
45#define REG_ARG0 REG_RDI
46#define REG_ARG1 REG_RSI
47#define REG_ARG2 REG_RDX
48#define REG_ARG3 REG_R10
49#define REG_ARG4 REG_R8
50#define REG_ARG5 REG_R9
51#endif
52
53#ifndef PR_SET_NO_NEW_PRIVS
54#define PR_SET_NO_NEW_PRIVS 38
55#endif
56
57#ifndef SYS_SECCOMP
58#define SYS_SECCOMP 1
59#endif
60
61static void emulator(int nr, siginfo_t *info, void *void_context)
62{
63 ucontext_t *ctx = (ucontext_t *)(void_context);
64 int syscall;
65 char *buf;
66 ssize_t bytes;
67 size_t len;
68 if (info->si_code != SYS_SECCOMP)
69 return;
70 if (!ctx)
71 return;
72 syscall = ctx->uc_mcontext.gregs[REG_SYSCALL];
73 buf = (char *) ctx->uc_mcontext.gregs[REG_ARG1];
74 len = (size_t) ctx->uc_mcontext.gregs[REG_ARG2];
75
76 if (syscall != __NR_write)
77 return;
78 if (ctx->uc_mcontext.gregs[REG_ARG0] != STDERR_FILENO)
79 return;
80 /* Redirect stderr messages to stdout. Doesn't handle EINTR, etc */
81 ctx->uc_mcontext.gregs[REG_RESULT] = -1;
82 if (write(STDOUT_FILENO, "[ERR] ", 6) > 0) {
83 bytes = write(STDOUT_FILENO, buf, len);
84 ctx->uc_mcontext.gregs[REG_RESULT] = bytes;
85 }
86 return;
87}
88
89static int install_emulator(void)
90{
91 struct sigaction act;
92 sigset_t mask;
93 memset(&act, 0, sizeof(act));
94 sigemptyset(&mask);
95 sigaddset(&mask, SIGSYS);
96
97 act.sa_sigaction = &emulator;
98 act.sa_flags = SA_SIGINFO;
99 if (sigaction(SIGSYS, &act, NULL) < 0) {
100 perror("sigaction");
101 return -1;
102 }
103 if (sigprocmask(SIG_UNBLOCK, &mask, NULL)) {
104 perror("sigprocmask");
105 return -1;
106 }
107 return 0;
108}
109
110static int install_filter(void)
111{
112 struct sock_filter filter[] = {
113 /* Grab the system call number */
114 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_nr),
115 /* Jump table for the allowed syscalls */
116 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 0, 1),
117 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
118#ifdef __NR_sigreturn
119 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 0, 1),
120 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
121#endif
122 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 0, 1),
123 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
124 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 0, 1),
125 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
126 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0),
127 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 3, 2),
128
129 /* Check that read is only using stdin. */
130 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
131 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 4, 0),
132 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
133
134 /* Check that write is only using stdout */
135 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
136 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0),
137 /* Trap attempts to write to stderr */
138 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 1, 2),
139
140 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
141 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP),
142 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
143 };
144 struct sock_fprog prog = {
145 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
146 .filter = filter,
147 };
148
149 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
150 perror("prctl(NO_NEW_PRIVS)");
151 return 1;
152 }
153
154
155 if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
156 perror("prctl");
157 return 1;
158 }
159 return 0;
160}
161
162#define payload(_c) (_c), sizeof((_c))
163int main(int argc, char **argv)
164{
165 char buf[4096];
166 ssize_t bytes = 0;
167 if (install_emulator())
168 return 1;
169 if (install_filter())
170 return 1;
171 syscall(__NR_write, STDOUT_FILENO,
172 payload("OHAI! WHAT IS YOUR NAME? "));
173 bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf));
174 syscall(__NR_write, STDOUT_FILENO, payload("HELLO, "));
175 syscall(__NR_write, STDOUT_FILENO, buf, bytes);
176 syscall(__NR_write, STDERR_FILENO,
177 payload("Error message going to STDERR\n"));
178 return 0;
179}
180#else /* SUPPORTED_ARCH */
181/*
182 * This sample is x86-only. Since kernel samples are compiled with the
183 * host toolchain, a non-x86 host will result in using only the main()
184 * below.
185 */
186int main(void)
187{
188 return 1;
189}
190#endif /* SUPPORTED_ARCH */