Move seccomp policy to bionic

Test: Built and checked booted
Change-Id: Iaec1265fe5a55c4df90ab9e45b010ef36faf6bba
diff --git a/libc/seccomp/seccomp_policy.cpp b/libc/seccomp/seccomp_policy.cpp
new file mode 100644
index 0000000..7f2cd91
--- /dev/null
+++ b/libc/seccomp/seccomp_policy.cpp
@@ -0,0 +1,147 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "seccomp_policy.h"
+
+#include <linux/audit.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+#include <sys/prctl.h>
+
+#include <vector>
+
+#include <android-base/logging.h>
+
+#if defined __arm__ || defined __aarch64__
+
+extern const struct sock_filter arm_filter[];
+extern const size_t arm_filter_size;
+extern const struct sock_filter arm64_filter[];
+extern const size_t arm64_filter_size;
+
+#define syscall_nr (offsetof(struct seccomp_data, nr))
+#define arch_nr (offsetof(struct seccomp_data, arch))
+
+typedef std::vector<sock_filter> filter;
+
+// We want to keep the below inline functions for debugging and future
+// development even though they are not all sed currently.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-function"
+
+static inline void Kill(filter& f) {
+    f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL));
+}
+
+static inline void Trap(filter& f) {
+    f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRAP));
+}
+
+static inline void Error(filter& f, __u16 retcode) {
+    f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ERRNO + retcode));
+}
+
+inline static void Trace(filter& f) {
+    f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE));
+}
+
+inline static void Allow(filter& f) {
+    f.push_back(BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW));
+}
+
+#pragma clang diagnostic pop
+
+inline static void ExamineSyscall(filter& f) {
+    f.push_back(BPF_STMT(BPF_LD|BPF_W|BPF_ABS, syscall_nr));
+}
+
+inline static int SetValidateArchitectureJumpTarget(size_t offset, filter& f) {
+    size_t jump_length = f.size() - offset - 1;
+    auto u8_jump_length = (__u8) jump_length;
+    if (u8_jump_length != jump_length) {
+        LOG(FATAL)
+            << "Can't set jump greater than 255 - actual jump is " <<  jump_length;
+        return -1;
+    }
+    f[offset] = BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, AUDIT_ARCH_ARM, u8_jump_length, 0);
+    return 0;
+}
+
+inline static size_t ValidateArchitectureAndJumpIfNeeded(filter& f) {
+    f.push_back(BPF_STMT(BPF_LD|BPF_W|BPF_ABS, arch_nr));
+
+    f.push_back(BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, AUDIT_ARCH_AARCH64, 2, 0));
+    f.push_back(BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, AUDIT_ARCH_ARM, 1, 0));
+    Trap(f);
+    return f.size() - 2;
+}
+
+static bool install_filter(filter const& f) {
+    struct sock_fprog prog = {
+        static_cast<unsigned short>(f.size()),
+        const_cast<struct sock_filter*>(&f[0]),
+    };
+
+    if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) < 0) {
+        PLOG(FATAL) << "Could not set seccomp filter of size " << f.size();
+        return false;
+    }
+
+    LOG(INFO) << "Global filter of size " << f.size() << " installed";
+    return true;
+}
+
+bool set_seccomp_filter() {
+    filter f;
+
+    // Note that for mixed 64/32 bit architectures, ValidateArchitecture inserts a
+    // jump that must be changed to point to the start of the 32-bit policy
+    // 32 bit syscalls will not hit the policy between here and the call to SetJump
+    auto offset_to_32bit_filter = ValidateArchitectureAndJumpIfNeeded(f);
+
+    // 64-bit filter
+    ExamineSyscall(f);
+
+    // arm64-only filter - autogenerated from bionic syscall usage
+    for (size_t i = 0; i < arm64_filter_size; ++i) {
+        f.push_back(arm64_filter[i]);
+    }
+    Trap(f);
+
+    if (SetValidateArchitectureJumpTarget(offset_to_32bit_filter, f) != 0) {
+        return -1;
+    }
+
+    // 32-bit filter
+    ExamineSyscall(f);
+
+    // arm32 filter - autogenerated from bionic syscall usage
+    for (size_t i = 0; i < arm_filter_size; ++i) {
+        f.push_back(arm_filter[i]);
+    }
+    Trap(f);
+
+    return install_filter(f);
+}
+
+#else // if defined __arm__ || defined __aarch64__
+
+bool set_seccomp_filter() {
+    LOG(INFO) << "Not setting seccomp filter - wrong architecture";
+    return true;
+}
+
+#endif