1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
#!/bin/sh -eu
#
# SPDX-License-Identifier: AGPL-3.0-or-later
#
# PASST - Plug A Simple Socket Transport
# for qemu/UNIX domain socket mode
#
# PASTA - Pack A Subtle Tap Abstraction
# for network namespace/tap device mode
#
# seccomp.sh - Build seccomp profiles from "#syscalls[:PROFILE]" code comments
#
# Copyright (c) 2021 Red Hat GmbH
# Author: Stefano Brivio <sbrivio@redhat.com>
TMP="$(mktemp)"
OUT="seccomp.h"
HEADER="/* This file was automatically generated by $(basename ${0}) */"
# Prefix for each profile: check that 'arch' in seccomp_data is matching
PRE='
struct sock_filter filter_@PROFILE@[] = {
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, arch))),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, PASST_AUDIT_ARCH, 0, @KILL@),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, nr))),
'
# Suffix for each profile: return actions
POST=' BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL_PROCESS),
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
};
'
# Syscall, @NR@: number, @ALLOW@: offset to RET_ALLOW, @NAME@: syscall name
CALL=' BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, @NR@, @ALLOW@, 0), /* @NAME@ */'
# Binary search tree node or leaf, @NR@: value, @R@: right jump, @L@: left jump
BST=' BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, @NR@, @R@, @L@),'
# cleanup() - Remove temporary file if it exists
cleanup() {
rm -f "${TMP}"
}
trap "cleanup" EXIT
# sub() - Substitute in-place file line with processed template line
# $1: Line number
# $2: Template name (variable name)
# $@: Replacement for @KEY@ in the form KEY:value
sub() {
IFS=
__line_no="${1}"
__template="$(eval printf '%s' "\${${2}}")"
shift; shift
sed -i "${__line_no}s#.*#${__template}#" "${TMP}"
for __def in ${@}; do
__key="@${__def%%:*}@"
__value="${__def#*:}"
sed -i "${__line_no}s/${__key}/${__value}/" "${TMP}"
done
unset IFS
}
# finish() - Finalise header file from temporary files with prefix and suffix
# $1: Variable name of prefix
# $@: Replacements for prefix variable
finish() {
IFS=
__out="$(eval printf '%s' "\${${1}}")"
shift
for __def in ${@}; do
__key="@${__def%%:*}@"
__value="${__def#*:}"
__out="$(printf '%s' "${__out}" | sed "s#${__key}#${__value}#")"
done
printf '%s\n' "${__out}" >> "${OUT}"
cat "${TMP}" >> "${OUT}"
rm "${TMP}"
printf '%s' "${POST}" >> "${OUT}"
unset IFS
}
# log2() - Binary logarithm
# $1: Operand
log2() {
__x=-1
__y=${1}
while [ ${__y} -gt 0 ]; do : $((__y >>= 1)); __x=$((__x + 1)); done
echo ${__x}
}
# cc_syscall_nr - Try to get syscall number from compiler
# $1: Name of syscall
cc_syscall_nr() {
__in="$(printf "#include <sys/syscall.h>\n__NR_%s" ${1})"
__out="$(echo "${__in}" | cc -E -xc - -o - | tail -1)"
[ "${__out}" = "__NR_$1" ] && return 1
echo "${__out}"
}
# gen_profile() - Build struct sock_filter for a single profile
# $1: Profile name
# $@: Names of allowed system calls, amount padded to next power of two
gen_profile() {
__profile="${1}"
shift
__statements_calls=${#}
__bst_levels=$(log2 $(( __statements_calls / 4 )) )
__statements_bst=$(( __statements_calls / 4 - 1 ))
__statements=$((__statements_calls + __statements_bst))
for __i in $(seq 1 ${__statements_bst} ); do
echo -1 >> "${TMP}"
done
for __i in $(seq 1 ${__statements_calls} ); do
__syscall_name="$(eval echo \${${__i}})"
if { ! command -V ausyscall >/dev/null 2>&1 || \
! ausyscall "${__syscall_name}" --exact >> "${TMP}"; } && \
! cc_syscall_nr "${__syscall_name}" >> "${TMP}"; then
echo "Cannot get syscall number for ${__syscall_name}"
exit 1
fi
eval __syscall_nr_$(tail -1 "${TMP}")="${__syscall_name}"
done
sort -go "${TMP}" "${TMP}"
__distance=$(( __statements_calls / 2 ))
__level_nodes=1
__ll=0
__line=1
for __level in $(seq 1 $(( __bst_levels - 1 )) ); do
# Nodes
__cmp_pos=${__distance}
for __node in $(seq 1 ${__level_nodes}); do
__cmp_line=$(( __statements_bst + __cmp_pos ))
__lr=$(( __ll + 1 ))
__nr="$(sed -n ${__cmp_line}p "${TMP}")"
sub ${__line} BST "NR:${__nr}" "L:${__ll}" "R:${__lr}"
__ll=${__lr}
__line=$(( __line + 1 ))
__cmp_pos=$(( __cmp_pos + __distance * 2 ))
done
__distance=$(( __distance / 2 ))
__level_nodes=$(( __level_nodes * 2 ))
done
# Leaves
__ll=$(( __level_nodes - 1 ))
__lr=$(( __ll + __distance - 1 ))
__cmp_pos=${__distance}
for __leaf in $(seq 1 ${__level_nodes}); do
__cmp_line=$(( __statements_bst + __cmp_pos ))
__nr="$(sed -n ${__cmp_line}p "${TMP}")"
sub ${__line} BST "NR:${__nr}" "L:${__ll}" "R:${__lr}"
__ll=$(( __lr + __distance - 1 ))
__lr=$(( __ll + __distance))
__line=$(( __line + 1 ))
__cmp_pos=$(( __cmp_pos + __distance * 2 ))
done
# Calls
for __i in $(seq $(( __statements_bst + 1 )) ${__statements}); do
__nr="$(sed -n ${__i}p "${TMP}")"
eval __name="\${__syscall_nr_${__nr}}"
__allow=$(( __statements - __i + 1 ))
sub ${__i} CALL "NR:${__nr}" "NAME:${__name}" "ALLOW:${__allow}"
done
finish PRE "PROFILE:${__profile}" "KILL:$(( __statements + 1))"
}
printf '%s\n' "${HEADER}" > "${OUT}"
__profiles="$(sed -n 's/[\t ]*\*[\t ]*#syscalls:\([^ ]*\).*/\1/p' *.[ch] | sort -u)"
for __p in ${__profiles}; do
__calls="$(sed -n 's/[\t ]*\*[\t ]*#syscalls\(:'"${__p}"'\|\)[\t ]\{1,\}\(.*\)/\2/p' *.[ch] | tr ' ' '\n' | sort -u)"
echo "seccomp profile ${__p} allows: ${__calls}" | tr '\n' ' ' | fmt -t
# Pad here to keep gen_profile() "simple"
__count=0
for __c in ${__calls}; do __count=$(( __count + 1 )); done
__padded=$(( 1 << (( $(log2 ${__count}) + 1 )) ))
for __i in $( seq ${__count} $(( __padded - 1 )) ); do
__calls="${__calls} tuxcall"
done
gen_profile "${__p}" ${__calls}
done
|
