148 lines
4.3 KiB
C++
148 lines
4.3 KiB
C++
/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "seccomp_policy.h"
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#include <linux/audit.h>
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#include <linux/filter.h>
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#include <linux/seccomp.h>
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#include <sys/prctl.h>
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#include <vector>
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#include <android-base/logging.h>
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#if defined __arm__ || defined __aarch64__
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extern const struct sock_filter arm_filter[];
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extern const size_t arm_filter_size;
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extern const struct sock_filter arm64_filter[];
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extern const size_t arm64_filter_size;
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#define syscall_nr (offsetof(struct seccomp_data, nr))
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#define arch_nr (offsetof(struct seccomp_data, arch))
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typedef std::vector<sock_filter> filter;
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// We want to keep the below inline functions for debugging and future
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// development even though they are not all sed currently.
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#pragma clang diagnostic push
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#pragma clang diagnostic ignored "-Wunused-function"
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static inline void Kill(filter& f) {
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f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL));
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}
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static inline void Trap(filter& f) {
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f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRAP));
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}
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static inline void Error(filter& f, __u16 retcode) {
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f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ERRNO + retcode));
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}
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inline static void Trace(filter& f) {
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f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE));
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}
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inline static void Allow(filter& f) {
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f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW));
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}
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#pragma clang diagnostic pop
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inline static void ExamineSyscall(filter& f) {
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f.push_back(BPF_STMT(BPF_LD|BPF_W|BPF_ABS, syscall_nr));
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}
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inline static int SetValidateArchitectureJumpTarget(size_t offset, filter& f) {
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size_t jump_length = f.size() - offset - 1;
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auto u8_jump_length = (__u8) jump_length;
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if (u8_jump_length != jump_length) {
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LOG(FATAL)
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<< "Can't set jump greater than 255 - actual jump is " << jump_length;
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return -1;
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}
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f[offset] = BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, AUDIT_ARCH_ARM, u8_jump_length, 0);
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return 0;
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}
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inline static size_t ValidateArchitectureAndJumpIfNeeded(filter& f) {
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f.push_back(BPF_STMT(BPF_LD|BPF_W|BPF_ABS, arch_nr));
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f.push_back(BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, AUDIT_ARCH_AARCH64, 2, 0));
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f.push_back(BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, AUDIT_ARCH_ARM, 1, 0));
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Trap(f);
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return f.size() - 2;
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}
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static bool install_filter(filter const& f) {
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struct sock_fprog prog = {
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static_cast<unsigned short>(f.size()),
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const_cast<struct sock_filter*>(&f[0]),
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};
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if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) < 0) {
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PLOG(FATAL) << "Could not set seccomp filter of size " << f.size();
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return false;
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}
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LOG(INFO) << "Global filter of size " << f.size() << " installed";
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return true;
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}
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bool set_seccomp_filter() {
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filter f;
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// Note that for mixed 64/32 bit architectures, ValidateArchitecture inserts a
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// jump that must be changed to point to the start of the 32-bit policy
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// 32 bit syscalls will not hit the policy between here and the call to SetJump
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auto offset_to_32bit_filter = ValidateArchitectureAndJumpIfNeeded(f);
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// 64-bit filter
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ExamineSyscall(f);
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// arm64-only filter - autogenerated from bionic syscall usage
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for (size_t i = 0; i < arm64_filter_size; ++i) {
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f.push_back(arm64_filter[i]);
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}
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Trap(f);
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if (SetValidateArchitectureJumpTarget(offset_to_32bit_filter, f) != 0) {
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return -1;
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}
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// 32-bit filter
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ExamineSyscall(f);
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// arm32 filter - autogenerated from bionic syscall usage
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for (size_t i = 0; i < arm_filter_size; ++i) {
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f.push_back(arm_filter[i]);
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}
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Trap(f);
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return install_filter(f);
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}
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#else // if defined __arm__ || defined __aarch64__
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bool set_seccomp_filter() {
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LOG(INFO) << "Not setting seccomp filter - wrong architecture";
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return true;
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}
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#endif
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