passt, pasta: Add seccomp support
List of allowed syscalls comes from comments in the form: #syscalls <list> for syscalls needed both in passt and pasta mode, and: #syscalls:pasta <list> #syscalls:passt <list> for syscalls specifically needed in pasta or passt mode only. seccomp.sh builds a list of BPF statements from those comments, prefixed by a binary search tree to keep lookup fast. While at it, clean up a bit the Makefile using wildcards. Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio
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seccomp.sh
Executable file
180
seccomp.sh
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#!/bin/sh -eu
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#
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# SPDX-License-Identifier: AGPL-3.0-or-later
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#
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# PASST - Plug A Simple Socket Transport
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# for qemu/UNIX domain socket mode
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#
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# PASTA - Pack A Subtle Tap Abstraction
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# for network namespace/tap device mode
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#
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# seccomp.sh - Build seccomp profiles from "#syscalls[:PROFILE]" comments in code
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#
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# Copyright (c) 2021 Red Hat GmbH
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# Author: Stefano Brivio <sbrivio@redhat.com>
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TMP="$(mktemp)"
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OUT="seccomp.h"
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HEADER="/* This file was automatically generated by $(basename ${0}) */"
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# Prefix for each profile: check that 'arch' in seccomp_data is matching
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PRE='
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struct sock_filter filter_@PROFILE@[] = {
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BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
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(offsetof(struct seccomp_data, arch))),
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BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, PASST_AUDIT_ARCH, 0, @KILL@),
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BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
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(offsetof(struct seccomp_data, nr))),
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'
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# Suffix for each profile: return actions
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POST=' BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL_PROCESS),
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BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
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};
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'
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# Syscall, @NR@: number, @ALLOW@: offset to RET_ALLOW, @NAME@: syscall name
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CALL=' BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, @NR@, @ALLOW@, 0), /* @NAME@ */'
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# Binary search tree node or leaf, @NR@: value, @R@: right jump, @L@: left jump
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BST=' BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, @NR@, @R@, @L@),'
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# sub() - Substitute in-place file line with processed template line
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# $1: Line number
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# $@: Replacement for @KEY@ in the form KEY:value
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sub() {
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IFS=
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__line_no="${1}"
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__template="$(eval printf '%s' "\${${2}}")"
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shift; shift
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sed -i "${__line_no}s#.*#${__template}#" "${TMP}"
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for __def in ${@}; do
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__key="@${__def%%:*}@"
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__value="${__def#*:}"
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sed -i "${__line_no}s/${__key}/${__value}/" "${TMP}"
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done
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unset IFS
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}
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# finish() - Finalise header file from temporary files with prefix and suffix
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# $1: Variable name of prefix
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# $@: Replacements for prefix variable
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finish() {
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IFS=
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__out="$(eval printf '%s' "\${${1}}")"
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shift
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for __def in ${@}; do
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__key="@${__def%%:*}@"
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__value="${__def#*:}"
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__out="$(printf '%s' "${__out}" | sed "s#${__key}#${__value}#")"
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done
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printf '%s\n' "${__out}" >> "${OUT}"
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cat "${TMP}" >> "${OUT}"
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rm "${TMP}"
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printf '%s' "${POST}" >> "${OUT}"
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unset IFS
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}
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# log2() - Binary logarithm
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# $1: Operand
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log2() {
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__x=-1
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__y=${1}
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while [ ${__y} -gt 0 ]; do : $((__y >>= 1)); __x=$((__x + 1)); done
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echo ${__x}
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}
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# gen_profile() - Build struct sock_filter for a single profile
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# $1: Profile name
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# $@: Names of allowed system calls, amount padded to next power of two
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gen_profile() {
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__profile="${1}"
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shift
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__statements_calls=${#}
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__bst_levels=$(log2 $(( __statements_calls / 4 )) )
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__statements_bst=$(( __statements_calls / 4 - 1 ))
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__statements=$((__statements_calls + __statements_bst))
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for __i in $(seq 1 ${__statements_bst} ); do
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echo -1 >> "${TMP}"
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done
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for __i in $(seq 1 ${__statements_calls} ); do
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ausyscall $(eval echo \${${__i}}) --exact >> "${TMP}"
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done
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sort -go "${TMP}" "${TMP}"
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__distance=$(( __statements_calls / 2 ))
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__level_nodes=1
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__ll=0
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__line=1
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for __level in $(seq 1 $(( __bst_levels - 1 )) ); do
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# Nodes
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__cmp_pos=${__distance}
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for __node in $(seq 1 ${__level_nodes}); do
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__cmp_line=$(( __statements_bst + __cmp_pos ))
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__lr=$(( __ll + 1 ))
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__nr="$(sed -n ${__cmp_line}p "${TMP}")"
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sub ${__line} BST "NR:${__nr}" "L:${__ll}" "R:${__lr}"
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__ll=${__lr}
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__line=$(( __line + 1 ))
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__cmp_pos=$(( __cmp_pos + __distance * 2 ))
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done
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__distance=$(( __distance / 2 ))
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__level_nodes=$(( __level_nodes * 2 ))
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done
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# Leaves
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__ll=$(( __level_nodes - 1 ))
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__lr=$(( __ll + __distance - 1 ))
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__cmp_pos=${__distance}
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for __leaf in $(seq 1 ${__level_nodes}); do
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__cmp_line=$(( __statements_bst + __cmp_pos ))
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__nr="$(sed -n ${__cmp_line}p "${TMP}")"
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sub ${__line} BST "NR:${__nr}" "L:${__ll}" "R:${__lr}"
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__ll=$(( __lr + __distance - 1 ))
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__lr=$(( __ll + __distance))
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__line=$(( __line + 1 ))
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__cmp_pos=$(( __cmp_pos + __distance * 2 ))
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done
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# Calls
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for __i in $(seq $(( __statements_bst + 1 )) ${__statements}); do
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__nr="$(sed -n ${__i}p "${TMP}")"
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__name=$(ausyscall ${__nr})
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__allow=$(( __statements - __i + 1 ))
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sub ${__i} CALL "NR:${__nr}" "NAME:${__name}" "ALLOW:${__allow}"
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done
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finish PRE "PROFILE:${__profile}" "KILL:$(( __statements + 1))"
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}
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printf '%s\n' "${HEADER}" > "${OUT}"
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__profiles="$(sed -n 's/[\t ]*\*[\t ]*#syscalls:\([^ ]*\).*/\1/p' *.[ch] | sort -u)"
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for __p in ${__profiles}; do
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__calls="$(sed -n 's/[\t ]*\*[\t ]*#syscalls\(:'"${__p}"'\|\)[\t ]\{1,\}\(.*\)/\2/p' *.[ch] | tr ' ' '\n' | sort -u)"
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echo "seccomp profile ${__p} allows: ${__calls}" | tr '\n' ' ' | fmt -t
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# Pad here to keep gen_profile() "simple"
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__count=0
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for __c in ${__calls}; do __count=$(( __count + 1 )); done
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__padded=$(( 1 << (( $(log2 ${__count}) + 1 )) ))
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for __i in $( seq ${__count} $(( __padded - 1 )) ); do
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__calls="${__calls} tuxcall"
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done
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gen_profile "${__p}" ${__calls}
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done
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