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authorWill Drewry <wad@chromium.org>2012-04-12 17:48:04 -0400
committerJames Morris <james.l.morris@oracle.com>2012-04-13 21:13:22 -0400
commit8ac270d1e29f0428228ab2b9a8ae5e1ed4a5cd84 (patch)
tree6deba4ed83da9ace758004b29d15aa0d2ec875a7 /samples/seccomp
parentc6cfbeb4029610c8c330c312dcf4d514cc067554 (diff)
Documentation: prctl/seccomp_filter
Documents how system call filtering using Berkeley Packet Filter programs works and how it may be used. Includes an example for x86 and a semi-generic example using a macro-based code generator. Acked-by: Eric Paris <eparis@redhat.com> Signed-off-by: Will Drewry <wad@chromium.org> Acked-by: Kees Cook <keescook@chromium.org> v18: - added acked by - update no new privs numbers v17: - remove @compat note and add Pitfalls section for arch checking (keescook@chromium.org) v16: - v15: - v14: - rebase/nochanges v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc v12: - comment on the ptrace_event use - update arch support comment - note the behavior of SECCOMP_RET_DATA when there are multiple filters (keescook@chromium.org) - lots of samples/ clean up incl 64-bit bpf-direct support (markus@chromium.org) - rebase to linux-next v11: - overhaul return value language, updates (keescook@chromium.org) - comment on do_exit(SIGSYS) v10: - update for SIGSYS - update for new seccomp_data layout - update for ptrace option use v9: - updated bpf-direct.c for SIGILL v8: - add PR_SET_NO_NEW_PRIVS to the samples. v7: - updated for all the new stuff in v7: TRAP, TRACE - only talk about PR_SET_SECCOMP now - fixed bad JLE32 check (coreyb@linux.vnet.ibm.com) - adds dropper.c: a simple system call disabler v6: - tweak the language to note the requirement of PR_SET_NO_NEW_PRIVS being called prior to use. (luto@mit.edu) v5: - update sample to use system call arguments - adds a "fancy" example using a macro-based generator - cleaned up bpf in the sample - update docs to mention arguments - fix prctl value (eparis@redhat.com) - language cleanup (rdunlap@xenotime.net) v4: - update for no_new_privs use - minor tweaks v3: - call out BPF <-> Berkeley Packet Filter (rdunlap@xenotime.net) - document use of tentative always-unprivileged - guard sample compilation for i386 and x86_64 v2: - move code to samples (corbet@lwn.net) Signed-off-by: James Morris <james.l.morris@oracle.com>
Diffstat (limited to 'samples/seccomp')
-rw-r--r--samples/seccomp/Makefile38
-rw-r--r--samples/seccomp/bpf-direct.c176
-rw-r--r--samples/seccomp/bpf-fancy.c102
-rw-r--r--samples/seccomp/bpf-helper.c89
-rw-r--r--samples/seccomp/bpf-helper.h238
-rw-r--r--samples/seccomp/dropper.c68
6 files changed, 711 insertions, 0 deletions
diff --git a/samples/seccomp/Makefile b/samples/seccomp/Makefile
new file mode 100644
index 000000000000..e8fe0f57b68f
--- /dev/null
+++ b/samples/seccomp/Makefile
@@ -0,0 +1,38 @@
1# kbuild trick to avoid linker error. Can be omitted if a module is built.
2obj- := dummy.o
3
4hostprogs-$(CONFIG_SECCOMP) := bpf-fancy dropper
5bpf-fancy-objs := bpf-fancy.o bpf-helper.o
6
7HOSTCFLAGS_bpf-fancy.o += -I$(objtree)/usr/include
8HOSTCFLAGS_bpf-fancy.o += -idirafter $(objtree)/include
9HOSTCFLAGS_bpf-helper.o += -I$(objtree)/usr/include
10HOSTCFLAGS_bpf-helper.o += -idirafter $(objtree)/include
11
12HOSTCFLAGS_dropper.o += -I$(objtree)/usr/include
13HOSTCFLAGS_dropper.o += -idirafter $(objtree)/include
14dropper-objs := dropper.o
15
16# bpf-direct.c is x86-only.
17ifeq ($(SRCARCH),x86)
18# List of programs to build
19hostprogs-$(CONFIG_SECCOMP) += bpf-direct
20bpf-direct-objs := bpf-direct.o
21endif
22
23HOSTCFLAGS_bpf-direct.o += -I$(objtree)/usr/include
24HOSTCFLAGS_bpf-direct.o += -idirafter $(objtree)/include
25
26# Try to match the kernel target.
27ifeq ($(CONFIG_64BIT),)
28HOSTCFLAGS_bpf-direct.o += -m32
29HOSTCFLAGS_dropper.o += -m32
30HOSTCFLAGS_bpf-helper.o += -m32
31HOSTCFLAGS_bpf-fancy.o += -m32
32HOSTLOADLIBES_bpf-direct += -m32
33HOSTLOADLIBES_bpf-fancy += -m32
34HOSTLOADLIBES_dropper += -m32
35endif
36
37# Tell kbuild to always build the programs
38always := $(hostprogs-y)
diff --git a/samples/seccomp/bpf-direct.c b/samples/seccomp/bpf-direct.c
new file mode 100644
index 000000000000..26f523e6ed74
--- /dev/null
+++ b/samples/seccomp/bpf-direct.c
@@ -0,0 +1,176 @@
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#define __USE_GNU 1
12#define _GNU_SOURCE 1
13
14#include <linux/types.h>
15#include <linux/filter.h>
16#include <linux/seccomp.h>
17#include <linux/unistd.h>
18#include <signal.h>
19#include <stdio.h>
20#include <stddef.h>
21#include <string.h>
22#include <sys/prctl.h>
23#include <unistd.h>
24
25#define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
26#define syscall_nr (offsetof(struct seccomp_data, nr))
27
28#if defined(__i386__)
29#define REG_RESULT REG_EAX
30#define REG_SYSCALL REG_EAX
31#define REG_ARG0 REG_EBX
32#define REG_ARG1 REG_ECX
33#define REG_ARG2 REG_EDX
34#define REG_ARG3 REG_ESI
35#define REG_ARG4 REG_EDI
36#define REG_ARG5 REG_EBP
37#elif defined(__x86_64__)
38#define REG_RESULT REG_RAX
39#define REG_SYSCALL REG_RAX
40#define REG_ARG0 REG_RDI
41#define REG_ARG1 REG_RSI
42#define REG_ARG2 REG_RDX
43#define REG_ARG3 REG_R10
44#define REG_ARG4 REG_R8
45#define REG_ARG5 REG_R9
46#else
47#error Unsupported platform
48#endif
49
50#ifndef PR_SET_NO_NEW_PRIVS
51#define PR_SET_NO_NEW_PRIVS 38
52#endif
53
54#ifndef SYS_SECCOMP
55#define SYS_SECCOMP 1
56#endif
57
58static void emulator(int nr, siginfo_t *info, void *void_context)
59{
60 ucontext_t *ctx = (ucontext_t *)(void_context);
61 int syscall;
62 char *buf;
63 ssize_t bytes;
64 size_t len;
65 if (info->si_code != SYS_SECCOMP)
66 return;
67 if (!ctx)
68 return;
69 syscall = ctx->uc_mcontext.gregs[REG_SYSCALL];
70 buf = (char *) ctx->uc_mcontext.gregs[REG_ARG1];
71 len = (size_t) ctx->uc_mcontext.gregs[REG_ARG2];
72
73 if (syscall != __NR_write)
74 return;
75 if (ctx->uc_mcontext.gregs[REG_ARG0] != STDERR_FILENO)
76 return;
77 /* Redirect stderr messages to stdout. Doesn't handle EINTR, etc */
78 ctx->uc_mcontext.gregs[REG_RESULT] = -1;
79 if (write(STDOUT_FILENO, "[ERR] ", 6) > 0) {
80 bytes = write(STDOUT_FILENO, buf, len);
81 ctx->uc_mcontext.gregs[REG_RESULT] = bytes;
82 }
83 return;
84}
85
86static int install_emulator(void)
87{
88 struct sigaction act;
89 sigset_t mask;
90 memset(&act, 0, sizeof(act));
91 sigemptyset(&mask);
92 sigaddset(&mask, SIGSYS);
93
94 act.sa_sigaction = &emulator;
95 act.sa_flags = SA_SIGINFO;
96 if (sigaction(SIGSYS, &act, NULL) < 0) {
97 perror("sigaction");
98 return -1;
99 }
100 if (sigprocmask(SIG_UNBLOCK, &mask, NULL)) {
101 perror("sigprocmask");
102 return -1;
103 }
104 return 0;
105}
106
107static int install_filter(void)
108{
109 struct sock_filter filter[] = {
110 /* Grab the system call number */
111 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_nr),
112 /* Jump table for the allowed syscalls */
113 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 0, 1),
114 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
115#ifdef __NR_sigreturn
116 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 0, 1),
117 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
118#endif
119 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 0, 1),
120 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
121 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 0, 1),
122 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
123 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0),
124 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 3, 2),
125
126 /* Check that read is only using stdin. */
127 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
128 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 4, 0),
129 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
130
131 /* Check that write is only using stdout */
132 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
133 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0),
134 /* Trap attempts to write to stderr */
135 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 1, 2),
136
137 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
138 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP),
139 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
140 };
141 struct sock_fprog prog = {
142 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
143 .filter = filter,
144 };
145
146 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
147 perror("prctl(NO_NEW_PRIVS)");
148 return 1;
149 }
150
151
152 if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
153 perror("prctl");
154 return 1;
155 }
156 return 0;
157}
158
159#define payload(_c) (_c), sizeof((_c))
160int main(int argc, char **argv)
161{
162 char buf[4096];
163 ssize_t bytes = 0;
164 if (install_emulator())
165 return 1;
166 if (install_filter())
167 return 1;
168 syscall(__NR_write, STDOUT_FILENO,
169 payload("OHAI! WHAT IS YOUR NAME? "));
170 bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf));
171 syscall(__NR_write, STDOUT_FILENO, payload("HELLO, "));
172 syscall(__NR_write, STDOUT_FILENO, buf, bytes);
173 syscall(__NR_write, STDERR_FILENO,
174 payload("Error message going to STDERR\n"));
175 return 0;
176}
diff --git a/samples/seccomp/bpf-fancy.c b/samples/seccomp/bpf-fancy.c
new file mode 100644
index 000000000000..8eb483aaec46
--- /dev/null
+++ b/samples/seccomp/bpf-fancy.c
@@ -0,0 +1,102 @@
1/*
2 * Seccomp BPF example using a macro-based generator.
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_ATTACH_SECCOMP_FILTER).
10 */
11
12#include <linux/filter.h>
13#include <linux/seccomp.h>
14#include <linux/unistd.h>
15#include <stdio.h>
16#include <string.h>
17#include <sys/prctl.h>
18#include <unistd.h>
19
20#include "bpf-helper.h"
21
22#ifndef PR_SET_NO_NEW_PRIVS
23#define PR_SET_NO_NEW_PRIVS 38
24#endif
25
26int main(int argc, char **argv)
27{
28 struct bpf_labels l;
29 static const char msg1[] = "Please type something: ";
30 static const char msg2[] = "You typed: ";
31 char buf[256];
32 struct sock_filter filter[] = {
33 /* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */
34 LOAD_SYSCALL_NR,
35 SYSCALL(__NR_exit, ALLOW),
36 SYSCALL(__NR_exit_group, ALLOW),
37 SYSCALL(__NR_write, JUMP(&l, write_fd)),
38 SYSCALL(__NR_read, JUMP(&l, read)),
39 DENY, /* Don't passthrough into a label */
40
41 LABEL(&l, read),
42 ARG(0),
43 JNE(STDIN_FILENO, DENY),
44 ARG(1),
45 JNE((unsigned long)buf, DENY),
46 ARG(2),
47 JGE(sizeof(buf), DENY),
48 ALLOW,
49
50 LABEL(&l, write_fd),
51 ARG(0),
52 JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
53 JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
54 DENY,
55
56 LABEL(&l, write_buf),
57 ARG(1),
58 JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
59 JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
60 JEQ((unsigned long)buf, JUMP(&l, buf_len)),
61 DENY,
62
63 LABEL(&l, msg1_len),
64 ARG(2),
65 JLT(sizeof(msg1), ALLOW),
66 DENY,
67
68 LABEL(&l, msg2_len),
69 ARG(2),
70 JLT(sizeof(msg2), ALLOW),
71 DENY,
72
73 LABEL(&l, buf_len),
74 ARG(2),
75 JLT(sizeof(buf), ALLOW),
76 DENY,
77 };
78 struct sock_fprog prog = {
79 .filter = filter,
80 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
81 };
82 ssize_t bytes;
83 bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
84
85 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
86 perror("prctl(NO_NEW_PRIVS)");
87 return 1;
88 }
89
90 if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
91 perror("prctl(SECCOMP)");
92 return 1;
93 }
94 syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
95 bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
96 bytes = (bytes > 0 ? bytes : 0);
97 syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
98 syscall(__NR_write, STDERR_FILENO, buf, bytes);
99 /* Now get killed */
100 syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
101 return 0;
102}
diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
new file mode 100644
index 000000000000..579cfe331886
--- /dev/null
+++ b/samples/seccomp/bpf-helper.c
@@ -0,0 +1,89 @@
1/*
2 * Seccomp BPF helper functions
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_ATTACH_SECCOMP_FILTER).
10 */
11
12#include <stdio.h>
13#include <string.h>
14
15#include "bpf-helper.h"
16
17int bpf_resolve_jumps(struct bpf_labels *labels,
18 struct sock_filter *filter, size_t count)
19{
20 struct sock_filter *begin = filter;
21 __u8 insn = count - 1;
22
23 if (count < 1)
24 return -1;
25 /*
26 * Walk it once, backwards, to build the label table and do fixups.
27 * Since backward jumps are disallowed by BPF, this is easy.
28 */
29 filter += insn;
30 for (; filter >= begin; --insn, --filter) {
31 if (filter->code != (BPF_JMP+BPF_JA))
32 continue;
33 switch ((filter->jt<<8)|filter->jf) {
34 case (JUMP_JT<<8)|JUMP_JF:
35 if (labels->labels[filter->k].location == 0xffffffff) {
36 fprintf(stderr, "Unresolved label: '%s'\n",
37 labels->labels[filter->k].label);
38 return 1;
39 }
40 filter->k = labels->labels[filter->k].location -
41 (insn + 1);
42 filter->jt = 0;
43 filter->jf = 0;
44 continue;
45 case (LABEL_JT<<8)|LABEL_JF:
46 if (labels->labels[filter->k].location != 0xffffffff) {
47 fprintf(stderr, "Duplicate label use: '%s'\n",
48 labels->labels[filter->k].label);
49 return 1;
50 }
51 labels->labels[filter->k].location = insn;
52 filter->k = 0; /* fall through */
53 filter->jt = 0;
54 filter->jf = 0;
55 continue;
56 }
57 }
58 return 0;
59}
60
61/* Simple lookup table for labels. */
62__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
63{
64 struct __bpf_label *begin = labels->labels, *end;
65 int id;
66 if (labels->count == 0) {
67 begin->label = label;
68 begin->location = 0xffffffff;
69 labels->count++;
70 return 0;
71 }
72 end = begin + labels->count;
73 for (id = 0; begin < end; ++begin, ++id) {
74 if (!strcmp(label, begin->label))
75 return id;
76 }
77 begin->label = label;
78 begin->location = 0xffffffff;
79 labels->count++;
80 return id;
81}
82
83void seccomp_bpf_print(struct sock_filter *filter, size_t count)
84{
85 struct sock_filter *end = filter + count;
86 for ( ; filter < end; ++filter)
87 printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
88 filter->code, filter->jt, filter->jf, filter->k);
89}
diff --git a/samples/seccomp/bpf-helper.h b/samples/seccomp/bpf-helper.h
new file mode 100644
index 000000000000..643279dd30fb
--- /dev/null
+++ b/samples/seccomp/bpf-helper.h
@@ -0,0 +1,238 @@
1/*
2 * Example wrapper around 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 * No guarantees are provided with respect to the correctness
12 * or functionality of this code.
13 */
14#ifndef __BPF_HELPER_H__
15#define __BPF_HELPER_H__
16
17#include <asm/bitsperlong.h> /* for __BITS_PER_LONG */
18#include <endian.h>
19#include <linux/filter.h>
20#include <linux/seccomp.h> /* for seccomp_data */
21#include <linux/types.h>
22#include <linux/unistd.h>
23#include <stddef.h>
24
25#define BPF_LABELS_MAX 256
26struct bpf_labels {
27 int count;
28 struct __bpf_label {
29 const char *label;
30 __u32 location;
31 } labels[BPF_LABELS_MAX];
32};
33
34int bpf_resolve_jumps(struct bpf_labels *labels,
35 struct sock_filter *filter, size_t count);
36__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label);
37void seccomp_bpf_print(struct sock_filter *filter, size_t count);
38
39#define JUMP_JT 0xff
40#define JUMP_JF 0xff
41#define LABEL_JT 0xfe
42#define LABEL_JF 0xfe
43
44#define ALLOW \
45 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
46#define DENY \
47 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
48#define JUMP(labels, label) \
49 BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
50 JUMP_JT, JUMP_JF)
51#define LABEL(labels, label) \
52 BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
53 LABEL_JT, LABEL_JF)
54#define SYSCALL(nr, jt) \
55 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (nr), 0, 1), \
56 jt
57
58/* Lame, but just an example */
59#define FIND_LABEL(labels, label) seccomp_bpf_label((labels), #label)
60
61#define EXPAND(...) __VA_ARGS__
62/* Map all width-sensitive operations */
63#if __BITS_PER_LONG == 32
64
65#define JEQ(x, jt) JEQ32(x, EXPAND(jt))
66#define JNE(x, jt) JNE32(x, EXPAND(jt))
67#define JGT(x, jt) JGT32(x, EXPAND(jt))
68#define JLT(x, jt) JLT32(x, EXPAND(jt))
69#define JGE(x, jt) JGE32(x, EXPAND(jt))
70#define JLE(x, jt) JLE32(x, EXPAND(jt))
71#define JA(x, jt) JA32(x, EXPAND(jt))
72#define ARG(i) ARG_32(i)
73#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
74
75#elif __BITS_PER_LONG == 64
76
77/* Ensure that we load the logically correct offset. */
78#if __BYTE_ORDER == __LITTLE_ENDIAN
79#define ENDIAN(_lo, _hi) _lo, _hi
80#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
81#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
82#elif __BYTE_ORDER == __BIG_ENDIAN
83#define ENDIAN(_lo, _hi) _hi, _lo
84#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
85#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
86#else
87#error "Unknown endianness"
88#endif
89
90union arg64 {
91 struct {
92 __u32 ENDIAN(lo32, hi32);
93 };
94 __u64 u64;
95};
96
97#define JEQ(x, jt) \
98 JEQ64(((union arg64){.u64 = (x)}).lo32, \
99 ((union arg64){.u64 = (x)}).hi32, \
100 EXPAND(jt))
101#define JGT(x, jt) \
102 JGT64(((union arg64){.u64 = (x)}).lo32, \
103 ((union arg64){.u64 = (x)}).hi32, \
104 EXPAND(jt))
105#define JGE(x, jt) \
106 JGE64(((union arg64){.u64 = (x)}).lo32, \
107 ((union arg64){.u64 = (x)}).hi32, \
108 EXPAND(jt))
109#define JNE(x, jt) \
110 JNE64(((union arg64){.u64 = (x)}).lo32, \
111 ((union arg64){.u64 = (x)}).hi32, \
112 EXPAND(jt))
113#define JLT(x, jt) \
114 JLT64(((union arg64){.u64 = (x)}).lo32, \
115 ((union arg64){.u64 = (x)}).hi32, \
116 EXPAND(jt))
117#define JLE(x, jt) \
118 JLE64(((union arg64){.u64 = (x)}).lo32, \
119 ((union arg64){.u64 = (x)}).hi32, \
120 EXPAND(jt))
121
122#define JA(x, jt) \
123 JA64(((union arg64){.u64 = (x)}).lo32, \
124 ((union arg64){.u64 = (x)}).hi32, \
125 EXPAND(jt))
126#define ARG(i) ARG_64(i)
127
128#else
129#error __BITS_PER_LONG value unusable.
130#endif
131
132/* Loads the arg into A */
133#define ARG_32(idx) \
134 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx))
135
136/* Loads hi into A and lo in X */
137#define ARG_64(idx) \
138 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)), \
139 BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \
140 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, HI_ARG(idx)), \
141 BPF_STMT(BPF_ST, 1) /* hi -> M[1] */
142
143#define JEQ32(value, jt) \
144 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 0, 1), \
145 jt
146
147#define JNE32(value, jt) \
148 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 1, 0), \
149 jt
150
151/* Checks the lo, then swaps to check the hi. A=lo,X=hi */
152#define JEQ64(lo, hi, jt) \
153 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
154 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
155 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 0, 2), \
156 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
157 jt, \
158 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
159
160#define JNE64(lo, hi, jt) \
161 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 5, 0), \
162 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
163 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 2, 0), \
164 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
165 jt, \
166 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
167
168#define JA32(value, jt) \
169 BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \
170 jt
171
172#define JA64(lo, hi, jt) \
173 BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (hi), 3, 0), \
174 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
175 BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (lo), 0, 2), \
176 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
177 jt, \
178 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
179
180#define JGE32(value, jt) \
181 BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \
182 jt
183
184#define JLT32(value, jt) \
185 BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \
186 jt
187
188/* Shortcut checking if hi > arg.hi. */
189#define JGE64(lo, hi, jt) \
190 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
191 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
192 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
193 BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 0, 2), \
194 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
195 jt, \
196 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
197
198#define JLT64(lo, hi, jt) \
199 BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
200 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
201 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
202 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
203 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
204 jt, \
205 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
206
207#define JGT32(value, jt) \
208 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \
209 jt
210
211#define JLE32(value, jt) \
212 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \
213 jt
214
215/* Check hi > args.hi first, then do the GE checking */
216#define JGT64(lo, hi, jt) \
217 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
218 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
219 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
220 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 0, 2), \
221 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
222 jt, \
223 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
224
225#define JLE64(lo, hi, jt) \
226 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 6, 0), \
227 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \
228 BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
229 BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
230 BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
231 jt, \
232 BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
233
234#define LOAD_SYSCALL_NR \
235 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
236 offsetof(struct seccomp_data, nr))
237
238#endif /* __BPF_HELPER_H__ */
diff --git a/samples/seccomp/dropper.c b/samples/seccomp/dropper.c
new file mode 100644
index 000000000000..c69c347c7011
--- /dev/null
+++ b/samples/seccomp/dropper.c
@@ -0,0 +1,68 @@
1/*
2 * Naive system call dropper built on seccomp_filter.
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 * When run, returns the specified errno for the specified
12 * system call number against the given architecture.
13 *
14 * Run this one as root as PR_SET_NO_NEW_PRIVS is not called.
15 */
16
17#include <errno.h>
18#include <linux/audit.h>
19#include <linux/filter.h>
20#include <linux/seccomp.h>
21#include <linux/unistd.h>
22#include <stdio.h>
23#include <stddef.h>
24#include <stdlib.h>
25#include <sys/prctl.h>
26#include <unistd.h>
27
28static int install_filter(int nr, int arch, int error)
29{
30 struct sock_filter filter[] = {
31 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
32 (offsetof(struct seccomp_data, arch))),
33 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
34 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
35 (offsetof(struct seccomp_data, nr))),
36 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
37 BPF_STMT(BPF_RET+BPF_K,
38 SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
39 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
40 };
41 struct sock_fprog prog = {
42 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
43 .filter = filter,
44 };
45 if (prctl(PR_SET_SECCOMP, 2, &prog)) {
46 perror("prctl");
47 return 1;
48 }
49 return 0;
50}
51
52int main(int argc, char **argv)
53{
54 if (argc < 5) {
55 fprintf(stderr, "Usage:\n"
56 "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
57 "Hint: AUDIT_ARCH_I386: 0x%X\n"
58 " AUDIT_ARCH_X86_64: 0x%X\n"
59 "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
60 return 1;
61 }
62 if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
63 strtol(argv[3], NULL, 0)))
64 return 1;
65 execv(argv[4], &argv[4]);
66 printf("Failed to execv\n");
67 return 255;
68}
generated by cgit v1.2.2 (git 2.25.0) at 2026-05-12 04:39:18 -0400