199 lines
6.5 KiB
C++
199 lines
6.5 KiB
C++
/*
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* \brief Generate seccomp filter policy for base-linux
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* \author Stefan Thoeni
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* \date 2019-12-13
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*/
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/*
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* Copyright (C) 2019 Genode Labs GmbH
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* Copyright (C) 2019 gapfruit AG
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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#include <stdio.h> /* printf */
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#include <seccomp.h> /* libseccomp */
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#include <asm/signal.h>
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#include <linux/sched.h>
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class Filter
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{
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private:
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scmp_filter_ctx _ctx = seccomp_init(SCMP_ACT_KILL_PROCESS);
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uint32_t _arch;
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void _add_allow_rule(int syscall_number)
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{
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int result = seccomp_rule_add(_ctx, SCMP_ACT_ALLOW, syscall_number, 0);
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if (result != 0) {
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fprintf(stderr, "Add rule failed for number %i\n", syscall_number);
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throw -102;
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}
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}
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void _add_allow_rule(int syscall_number, scmp_arg_cmp c1)
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{
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int result = seccomp_rule_add(_ctx, SCMP_ACT_ALLOW, syscall_number, 1, c1);
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if (result != 0) {
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fprintf(stderr, "Add rule failed for number %i\n", syscall_number);
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throw -102;
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}
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}
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void _add_allow_rule(int syscall_number, scmp_arg_cmp c1, scmp_arg_cmp c2)
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{
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int result = seccomp_rule_add(_ctx, SCMP_ACT_ALLOW, syscall_number, 2, c1, c2);
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if (result != 0) {
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fprintf(stderr, "Add rule failed for number %i\n", syscall_number);
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throw -102;
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}
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}
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public:
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Filter(uint32_t arch)
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: _arch(arch)
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{
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}
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int create()
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{
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/* Kill the process if the filter architecture does not fit. */
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if (seccomp_attr_set(_ctx, SCMP_FLTATR_ACT_BADARCH, SCMP_ACT_KILL_PROCESS) != 0) {
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fprintf(stderr, "Failed to set bad architecture action\n");
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throw -103;
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}
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/* Remove the default architecture (e.g. native architecture) from the filter.*/
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if (seccomp_arch_remove(_ctx, SCMP_ARCH_NATIVE) != 0) {
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fprintf(stderr, "Failed to remove default architecture\n");
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throw -103;
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}
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/* Add the desired architecture to the filter.*/
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if (seccomp_arch_add(_ctx, _arch) != 0) {
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fprintf(stderr, "Failed to add architecture\n");
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throw -103;
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}
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/* This syscall is safe as it create a socket pair in the
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* process */
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_add_allow_rule(SCMP_SYS(socketpair));
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/* These syscalls should be safe as they only access already open sockets. */
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_add_allow_rule(SCMP_SYS(sendmsg));
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_add_allow_rule(SCMP_SYS(recvmsg));
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_add_allow_rule(SCMP_SYS(write));
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_add_allow_rule(SCMP_SYS(poll));
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_add_allow_rule(SCMP_SYS(epoll_create));
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_add_allow_rule(SCMP_SYS(epoll_ctl));
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_add_allow_rule(SCMP_SYS(epoll_wait));
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_add_allow_rule(SCMP_SYS(close));
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_add_allow_rule(SCMP_SYS(munmap));
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_add_allow_rule(SCMP_SYS(dup));
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_add_allow_rule(SCMP_SYS(fstat));
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_add_allow_rule(SCMP_SYS(fstat64));
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/* This syscall is used to wait for a condition. This should be safe. */
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_add_allow_rule(SCMP_SYS(futex));
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/* This syscall ends the program. This should be safe */
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_add_allow_rule(SCMP_SYS(exit));
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/* These syscalls are used to react to signals. They should be safe */
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_add_allow_rule(SCMP_SYS(sigaltstack));
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_add_allow_rule(SCMP_SYS(rt_sigaction));
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/* This syscall is used to sleep. This should be safe */
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_add_allow_rule(SCMP_SYS(nanosleep));
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/* These syscall allow access to global information. We would like
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* to reduced this. */
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_add_allow_rule(SCMP_SYS(getpid));
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_add_allow_rule(SCMP_SYS(gettid));
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_add_allow_rule(SCMP_SYS(gettimeofday));
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_add_allow_rule(SCMP_SYS(getpeername));
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int clone_flags = CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND
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| CLONE_THREAD | CLONE_SYSVSEM;
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switch (_arch)
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{
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case SCMP_ARCH_X86:
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{
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/* The tgkill syscall must be made safe by restricting parameters.
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* Genode uses LX_SIGCANCEL alias SIGRTMIN to cancel threads
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* the 0xCAFEAFFE will be replaced with the process ID to restrict
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* tgkill to the process (= thread group). */
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_add_allow_rule(SCMP_SYS(tgkill), SCMP_CMP32(0, SCMP_CMP_EQ, 0xCAFEAFFE),
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SCMP_CMP32(2, SCMP_CMP_EQ, SIGRTMIN));
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/* The clone syscall must be made safe by restricting parameters
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* The specified flags only allow creation of new threads. */
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_add_allow_rule(SCMP_SYS(clone), SCMP_CMP32(0, SCMP_CMP_EQ, clone_flags));
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/* The nmap syscall has a different name on different architectures
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* but it slould be save as it only uses an already open socket. */
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_add_allow_rule(SCMP_SYS(mmap2));
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}
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break;
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case SCMP_ARCH_X86_64:
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{
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/* The tgkill syscall must be made safe by restricting parameters.
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* Genode uses LX_SIGCANCEL alias SIGRTMIN to cancel threads
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* the 0xCAFEAFFE will be replaced with the process ID to restrict
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* tgkill to the process (= thread group). */
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_add_allow_rule(SCMP_SYS(tgkill), SCMP_CMP64(0, SCMP_CMP_EQ, 0xCAFEAFFE),
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SCMP_CMP64(2, SCMP_CMP_EQ, SIGRTMIN));
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/* The clone syscall must be made safe by restricting parameters
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* The specified flags only allow creation of new threads. */
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_add_allow_rule(SCMP_SYS(clone), SCMP_CMP64(0, SCMP_CMP_EQ, clone_flags));
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/* The nmap syscall has a different name on different architectures
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* but it slould be save as it only uses an already open socket. */
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_add_allow_rule(SCMP_SYS(mmap));
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}
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break;
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case SCMP_ARCH_ARM:
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{
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/* The tgkill syscall must be made safe by restricting parameters.
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* Genode uses LX_SIGCANCEL alias SIGRTMIN to cancel threads
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* the 0xCAFEAFFE will be replaced with the process ID to restrict
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* tgkill to the process (= thread group). */
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_add_allow_rule(SCMP_SYS(tgkill), SCMP_CMP32(0, SCMP_CMP_EQ, 0xCAFEAFFE),
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SCMP_CMP32(2, SCMP_CMP_EQ, SIGRTMIN));
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/* The clone syscall must be made safe by restricting parameters
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* The specified flags only allow creation of new threads. */
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_add_allow_rule(SCMP_SYS(clone), SCMP_CMP32(0, SCMP_CMP_EQ, clone_flags));
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/* The nmap2 syscall has a different name on different architectures
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* but it slould be save as it only uses an already open socket. */
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_add_allow_rule(SCMP_SYS(mmap2));
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/* This syscall is only used on ARM. */
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_add_allow_rule(SCMP_SYS(cacheflush));
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/* This syscall is only used on ARM. */
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_add_allow_rule(SCMP_SYS(sigreturn));
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}
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break;
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default:
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fprintf(stderr, "Unsupported architecture\n");
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throw -104;
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}
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// build and export
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seccomp_export_bpf(_ctx, 1);
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return 0;
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}
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};
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