Merge tag 'pxa-dt-4.21' of https://github.com/rjarzmik/linux into next/dt
[muen/linux.git] / samples / seccomp / bpf-direct.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Seccomp filter example for x86 (32-bit and 64-bit) with BPF macros
4  *
5  * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
6  * Author: Will Drewry <wad@chromium.org>
7  *
8  * The code may be used by anyone for any purpose,
9  * and can serve as a starting point for developing
10  * applications using prctl(PR_SET_SECCOMP, 2, ...).
11  */
12 #if defined(__i386__) || defined(__x86_64__)
13 #define SUPPORTED_ARCH 1
14 #endif
15
16 #if defined(SUPPORTED_ARCH)
17 #define __USE_GNU 1
18 #define _GNU_SOURCE 1
19
20 #include <linux/types.h>
21 #include <linux/filter.h>
22 #include <linux/seccomp.h>
23 #include <linux/unistd.h>
24 #include <signal.h>
25 #include <stdio.h>
26 #include <stddef.h>
27 #include <string.h>
28 #include <sys/prctl.h>
29 #include <unistd.h>
30
31 #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
32 #define syscall_nr (offsetof(struct seccomp_data, nr))
33
34 #if defined(__i386__)
35 #define REG_RESULT      REG_EAX
36 #define REG_SYSCALL     REG_EAX
37 #define REG_ARG0        REG_EBX
38 #define REG_ARG1        REG_ECX
39 #define REG_ARG2        REG_EDX
40 #define REG_ARG3        REG_ESI
41 #define REG_ARG4        REG_EDI
42 #define REG_ARG5        REG_EBP
43 #elif defined(__x86_64__)
44 #define REG_RESULT      REG_RAX
45 #define REG_SYSCALL     REG_RAX
46 #define REG_ARG0        REG_RDI
47 #define REG_ARG1        REG_RSI
48 #define REG_ARG2        REG_RDX
49 #define REG_ARG3        REG_R10
50 #define REG_ARG4        REG_R8
51 #define REG_ARG5        REG_R9
52 #endif
53
54 #ifndef PR_SET_NO_NEW_PRIVS
55 #define PR_SET_NO_NEW_PRIVS 38
56 #endif
57
58 #ifndef SYS_SECCOMP
59 #define SYS_SECCOMP 1
60 #endif
61
62 static void emulator(int nr, siginfo_t *info, void *void_context)
63 {
64         ucontext_t *ctx = (ucontext_t *)(void_context);
65         int syscall;
66         char *buf;
67         ssize_t bytes;
68         size_t len;
69         if (info->si_code != SYS_SECCOMP)
70                 return;
71         if (!ctx)
72                 return;
73         syscall = ctx->uc_mcontext.gregs[REG_SYSCALL];
74         buf = (char *) ctx->uc_mcontext.gregs[REG_ARG1];
75         len = (size_t) ctx->uc_mcontext.gregs[REG_ARG2];
76
77         if (syscall != __NR_write)
78                 return;
79         if (ctx->uc_mcontext.gregs[REG_ARG0] != STDERR_FILENO)
80                 return;
81         /* Redirect stderr messages to stdout. Doesn't handle EINTR, etc */
82         ctx->uc_mcontext.gregs[REG_RESULT] = -1;
83         if (write(STDOUT_FILENO, "[ERR] ", 6) > 0) {
84                 bytes = write(STDOUT_FILENO, buf, len);
85                 ctx->uc_mcontext.gregs[REG_RESULT] = bytes;
86         }
87         return;
88 }
89
90 static int install_emulator(void)
91 {
92         struct sigaction act;
93         sigset_t mask;
94         memset(&act, 0, sizeof(act));
95         sigemptyset(&mask);
96         sigaddset(&mask, SIGSYS);
97
98         act.sa_sigaction = &emulator;
99         act.sa_flags = SA_SIGINFO;
100         if (sigaction(SIGSYS, &act, NULL) < 0) {
101                 perror("sigaction");
102                 return -1;
103         }
104         if (sigprocmask(SIG_UNBLOCK, &mask, NULL)) {
105                 perror("sigprocmask");
106                 return -1;
107         }
108         return 0;
109 }
110
111 static int install_filter(void)
112 {
113         struct sock_filter filter[] = {
114                 /* Grab the system call number */
115                 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_nr),
116                 /* Jump table for the allowed syscalls */
117                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 0, 1),
118                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
119 #ifdef __NR_sigreturn
120                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 0, 1),
121                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
122 #endif
123                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 0, 1),
124                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
125                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 0, 1),
126                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
127                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0),
128                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 3, 2),
129
130                 /* Check that read is only using stdin. */
131                 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
132                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 4, 0),
133                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
134
135                 /* Check that write is only using stdout */
136                 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
137                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0),
138                 /* Trap attempts to write to stderr */
139                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 1, 2),
140
141                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
142                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP),
143                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
144         };
145         struct sock_fprog prog = {
146                 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
147                 .filter = filter,
148         };
149
150         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
151                 perror("prctl(NO_NEW_PRIVS)");
152                 return 1;
153         }
154
155
156         if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
157                 perror("prctl");
158                 return 1;
159         }
160         return 0;
161 }
162
163 #define payload(_c) (_c), sizeof((_c))
164 int main(int argc, char **argv)
165 {
166         char buf[4096];
167         ssize_t bytes = 0;
168         if (install_emulator())
169                 return 1;
170         if (install_filter())
171                 return 1;
172         syscall(__NR_write, STDOUT_FILENO,
173                 payload("OHAI! WHAT IS YOUR NAME? "));
174         bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf));
175         syscall(__NR_write, STDOUT_FILENO, payload("HELLO, "));
176         syscall(__NR_write, STDOUT_FILENO, buf, bytes);
177         syscall(__NR_write, STDERR_FILENO,
178                 payload("Error message going to STDERR\n"));
179         return 0;
180 }
181 #else   /* SUPPORTED_ARCH */
182 /*
183  * This sample is x86-only.  Since kernel samples are compiled with the
184  * host toolchain, a non-x86 host will result in using only the main()
185  * below.
186  */
187 int main(void)
188 {
189         return 1;
190 }
191 #endif  /* SUPPORTED_ARCH */