aboutgitcodebugslistschat
path: root/seccomp.sh
blob: 38aa82651166d8cd9c91e0ca6f73dc24a4860cb2 (plain) (blame)
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
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
#!/bin/sh -eu
#
# SPDX-License-Identifier: GPL-2.0-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="$(mktemp)"
IN="$@"
OUT="$(mktemp)"

[ -z "${ARCH}" ] && ARCH="$(uname -m)"
[ -z "${CC}" ] && CC="cc"

HEADER="/* This file was automatically generated by $(basename ${0}) */

#ifndef AUDIT_ARCH_PPC64LE
#define AUDIT_ARCH_PPC64LE (AUDIT_ARCH_PPC64 | __AUDIT_ARCH_LE)
#endif"

# Prefix for each profile: check that 'arch' in seccomp_data is matching
PRE='
struct sock_filter filter_@PROFILE@[] = {
	/* cppcheck-suppress [badBitmaskCheck, unmatchedSuppression] */
	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@),
	/* cppcheck-suppress [badBitmaskCheck, unmatchedSuppression] */
	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 "${TMP}" "${OUT}"
}
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}"

	IFS=' '
	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

	IFS=' '
	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}
}

# syscall_nr - Get syscall number from compiler
# $1:	Name of syscall
syscall_nr() {
	__in="$(printf "#include <asm-generic/unistd.h>\n#include <sys/syscall.h>\n__NR_%s" ${1})"
	__out="$(echo "${__in}" | ${CC} -E -xc - -o - | tail -1)"
	[ "${__out}" = "__NR_$1" ] && return 1

	# Output might be in the form "(x + y)" (seen on armv6l, armv7l)
	__out="$(eval echo $((${__out})))"
	echo "${__out}"
}

filter() {
	__filtered=
	for __c in ${@}; do
		__arch_match=0
		case ${__c} in
		*:*)
			case ${__c} in
			${ARCH}:*)
				__arch_match=1
				__c=${__c##*:}
				;;
			esac
			;;
		*)
			__arch_match=1
			;;
		esac
		[ ${__arch_match} -eq 0 ] && continue

		IFS='| '
		__found=0
		for __name in ${__c}; do
			syscall_nr "${__name}" >/dev/null && __found=1 && break
		done
		unset IFS

		if [ ${__found} -eq 0 ]; then
			echo
			echo "Warning: no syscall number for ${__c}" >&2
			echo "  none of these syscalls will be allowed" >&2
			continue
		fi

		__filtered="${__filtered} ${__name}"
	done

	echo "${__filtered}" | tr ' ' '\n' | sort -u
}

# 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 ! 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' ${IN} | sort -u)"
for __p in ${__profiles}; do
	__calls="$(sed -n 's/[\t ]*\*[\t ]*#syscalls\(:'"${__p}"'\|\)[\t ]\{1,\}\(.*\)/\2/p' ${IN})"
	__calls="${__calls} ${EXTRA_SYSCALLS:-}"
	__calls="$(filter ${__calls})"

	cols="$(stty -a | sed -n 's/.*columns \([0-9]*\).*/\1/p' || :)" 2>/dev/null
	case $cols in [0-9]*) col_args="-w ${cols}";; *) col_args="";; esac
	echo "seccomp profile ${__p} allows: ${__calls}" | tr '\n' ' ' | fmt -t ${col_args}

	# 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} read"
	done

	gen_profile "${__p}" ${__calls}
done

mv "${OUT}" seccomp.h