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sandboxed-api/sandboxed_api/sandbox2/policybuilder.cc
Christian Blichmann e8cadf8f7d Allow mprotect(_, _, PROT_READ) for all static binaries 
Newer toolchains/libcs will use this syscall on x86-64 as well.

PiperOrigin-RevId: 428705078
Change-Id: I705efe37db9ebdd922036b39e4fb3c22dc749a1a
2022-02-15 00:14:25 -08:00

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// Copyright 2019 Google LLC
//
// 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
//
// https://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 "sandboxed_api/sandbox2/policybuilder.h"
#include <asm/ioctls.h> // For TCGETS
#include <fcntl.h> // For the fcntl flags
#include <linux/filter.h>
#include <linux/futex.h>
#include <linux/net.h> // For SYS_CONNECT
#include <linux/random.h> // For GRND_NONBLOCK
#include <sys/mman.h> // For mmap arguments
#include <sys/socket.h>
#include <syscall.h>
#include <array>
#include <csignal>
#include <cstdint>
#include <deque>
#include <utility>
#include "absl/memory/memory.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/escaping.h"
#include "absl/strings/match.h"
#include "absl/strings/string_view.h"
#include "sandboxed_api/config.h"
#include "sandboxed_api/sandbox2/namespace.h"
#include "sandboxed_api/sandbox2/util/bpf_helper.h"
#include "sandboxed_api/util/path.h"
#include "sandboxed_api/util/status_macros.h"
#if defined(SAPI_X86_64)
#include <asm/prctl.h>
#elif defined(SAPI_PPC64_LE)
#include <asm/termbits.h> // On PPC, TCGETS macro needs termios
#endif
namespace sandbox2 {
namespace {
namespace file = ::sapi::file;
constexpr std::array<uint32_t, 2> kMmapSyscalls = {
#ifdef __NR_mmap2
__NR_mmap2,
#endif
#ifdef __NR_mmap
__NR_mmap,
#endif
};
bool CheckBpfBounds(const sock_filter& filter, size_t max_jmp) {
if (BPF_CLASS(filter.code) == BPF_JMP) {
if (BPF_OP(filter.code) == BPF_JA) {
return filter.k <= max_jmp;
}
return filter.jt <= max_jmp && filter.jf <= max_jmp;
}
return true;
}
} // namespace
PolicyBuilder& PolicyBuilder::AllowSyscall(uint32_t num) {
if (handled_syscalls_.insert(num).second) {
user_policy_.insert(user_policy_.end(), {SYSCALL(num, ALLOW)});
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowSyscalls(absl::Span<const uint32_t> nums) {
for (auto num : nums) {
AllowSyscall(num);
}
return *this;
}
PolicyBuilder& PolicyBuilder::BlockSyscallsWithErrno(
absl::Span<const uint32_t> nums, int error) {
for (auto num : nums) {
AllowSyscall(num);
}
return *this;
}
PolicyBuilder& PolicyBuilder::BlockSyscallWithErrno(uint32_t num, int error) {
if (handled_syscalls_.insert(num).second) {
user_policy_.insert(user_policy_.end(), {SYSCALL(num, ERRNO(error))});
if (num == __NR_bpf) {
user_policy_handles_bpf_ = true;
}
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowExit() {
return AllowSyscalls({__NR_exit, __NR_exit_group});
}
PolicyBuilder& PolicyBuilder::AllowScudoMalloc() {
AllowTime();
AllowSyscalls({__NR_munmap, __NR_nanosleep});
AllowFutexOp(FUTEX_WAKE);
AllowLimitedMadvise();
AllowGetRandom();
AllowWipeOnFork();
return AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(2), // prot
JEQ32(PROT_NONE, JUMP(&labels, prot_none)),
JNE32(PROT_READ | PROT_WRITE, JUMP(&labels, mmap_end)),
// PROT_READ | PROT_WRITE
ARG_32(3), // flags
BPF_STMT(BPF_ALU | BPF_AND | BPF_K,
~uint32_t{MAP_FIXED | MAP_NORESERVE}),
JEQ32(MAP_PRIVATE | MAP_ANONYMOUS, ALLOW),
JUMP(&labels, mmap_end),
// PROT_NONE
LABEL(&labels, prot_none),
ARG_32(3), // flags
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, ALLOW),
LABEL(&labels, mmap_end),
};
});
}
PolicyBuilder& PolicyBuilder::AllowTcMalloc() {
AllowTime();
AllowRestartableSequences(kRequireFastFences);
AllowSyscalls(
{__NR_munmap, __NR_nanosleep, __NR_brk, __NR_mincore, __NR_membarrier});
AllowLimitedMadvise();
AddPolicyOnSyscall(__NR_mprotect, {
ARG_32(2),
JEQ32(PROT_READ | PROT_WRITE, ALLOW),
JEQ32(PROT_NONE, ALLOW),
});
return AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(2), // prot
JEQ32(PROT_NONE, JUMP(&labels, prot_none)),
JNE32(PROT_READ | PROT_WRITE, JUMP(&labels, mmap_end)),
// PROT_READ | PROT_WRITE
ARG_32(3), // flags
JNE32(MAP_ANONYMOUS | MAP_PRIVATE, JUMP(&labels, mmap_end)),
ALLOW,
// PROT_NONE
LABEL(&labels, prot_none),
ARG_32(3), // flags
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, ALLOW),
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE, ALLOW),
LABEL(&labels, mmap_end),
};
});
}
PolicyBuilder& PolicyBuilder::AllowSystemMalloc() {
AllowSyscalls({__NR_munmap, __NR_brk});
AllowFutexOp(FUTEX_WAKE);
AddPolicyOnSyscall(__NR_mremap, {
ARG_32(3),
JEQ32(MREMAP_MAYMOVE, ALLOW),
});
return AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(2), // prot
JEQ32(PROT_NONE, JUMP(&labels, prot_none)),
JNE32(PROT_READ | PROT_WRITE, JUMP(&labels, mmap_end)),
// PROT_READ | PROT_WRITE
ARG_32(3), // flags
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE, ALLOW),
// PROT_NONE
LABEL(&labels, prot_none),
ARG_32(3), // flags
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, ALLOW),
LABEL(&labels, mmap_end),
};
});
return *this;
}
PolicyBuilder& PolicyBuilder::AllowLlvmSanitizers() {
if constexpr (sapi::sanitizers::IsAny()) {
// *san use a custom allocator that runs mmap under the hood. For example:
// https://github.com/llvm/llvm-project/blob/596d534ac3524052df210be8d3c01a33b2260a42/compiler-rt/lib/asan/asan_allocator.cpp#L980
// https://github.com/llvm/llvm-project/blob/62ec4ac90738a5f2d209ed28c822223e58aaaeb7/compiler-rt/lib/sanitizer_common/sanitizer_allocator_secondary.h#L98
AllowMmap();
AddPolicyOnSyscall(__NR_madvise, {
ARG_32(2),
JEQ32(MADV_DONTDUMP, ALLOW),
JEQ32(MADV_NOHUGEPAGE, ALLOW),
});
// Sanitizers read from /proc. For example:
// https://github.com/llvm-mirror/compiler-rt/blob/69445f095c22aac2388f939bedebf224a6efcdaf/lib/sanitizer_common/sanitizer_linux.cpp#L1101
AddDirectory("/proc");
}
if constexpr (sapi::sanitizers::IsASan()) {
AllowSyscall(__NR_sigaltstack);
}
if constexpr (sapi::sanitizers::IsTSan()) {
AllowSyscall(__NR_munmap);
AddPolicyOnSyscall(__NR_mprotect,
{
ARG_32(2),
BPF_STMT(BPF_AND | BPF_ALU | BPF_K,
~uint32_t{PROT_READ | PROT_WRITE}),
JEQ32(0, ALLOW),
});
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowLimitedMadvise() {
return AddPolicyOnSyscall(__NR_madvise, {
ARG_32(2),
JEQ32(MADV_DONTNEED, ALLOW),
JEQ32(MADV_REMOVE, ALLOW),
JEQ32(MADV_NOHUGEPAGE, ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowMmap() {
return AllowSyscalls(kMmapSyscalls);
}
PolicyBuilder& PolicyBuilder::AllowOpen() {
#ifdef __NR_open
AllowSyscall(__NR_open);
#endif
#ifdef __NR_openat
AllowSyscall(__NR_openat);
#endif
return *this;
}
PolicyBuilder& PolicyBuilder::AllowStat() {
#ifdef __NR_fstat
AllowSyscall(__NR_fstat);
#endif
#ifdef __NR_fstat64
AllowSyscall(__NR_fstat64);
#endif
#ifdef __NR_fstatat
AllowSyscall(__NR_fstatat);
#endif
#ifdef __NR_fstatat64
AllowSyscall(__NR_fstatat64);
#endif
#ifdef __NR_lstat
AllowSyscall(__NR_lstat);
#endif
#ifdef __NR_lstat64
AllowSyscall(__NR_lstat64);
#endif
#ifdef __NR_newfstatat
AllowSyscall(__NR_newfstatat);
#endif
#ifdef __NR_oldfstat
AllowSyscall(__NR_oldfstat);
#endif
#ifdef __NR_oldlstat
AllowSyscall(__NR_oldlstat);
#endif
#ifdef __NR_oldstat
AllowSyscall(__NR_oldstat);
#endif
#ifdef __NR_stat
AllowSyscall(__NR_stat);
#endif
#ifdef __NR_stat64
AllowSyscall(__NR_stat64);
#endif
#ifdef __NR_statfs
AllowSyscall(__NR_statfs);
#endif
#ifdef __NR_statfs64
AllowSyscall(__NR_statfs64);
#endif
return *this;
}
PolicyBuilder& PolicyBuilder::AllowAccess() {
#ifdef __NR_access
AllowSyscall(__NR_access);
#endif
#ifdef __NR_faccessat
AllowSyscall(__NR_faccessat);
#endif
return *this;
}
PolicyBuilder& PolicyBuilder::AllowRead() {
return AllowSyscalls({
__NR_read,
__NR_readv,
__NR_preadv,
__NR_pread64,
});
}
PolicyBuilder& PolicyBuilder::AllowWrite() {
return AllowSyscalls({
__NR_write,
__NR_writev,
__NR_pwritev,
__NR_pwrite64,
});
}
PolicyBuilder& PolicyBuilder::AllowReaddir() {
return AllowSyscalls({
#ifdef __NR_getdents
__NR_getdents,
#endif
#ifdef __NR_getdents64
__NR_getdents64,
#endif
});
}
PolicyBuilder& PolicyBuilder::AllowSafeFcntl() {
return AddPolicyOnSyscalls({__NR_fcntl,
#ifdef __NR_fcntl64
__NR_fcntl64
#endif
},
{
ARG_32(1),
JEQ32(F_GETFD, ALLOW),
JEQ32(F_SETFD, ALLOW),
JEQ32(F_GETFL, ALLOW),
JEQ32(F_SETFL, ALLOW),
JEQ32(F_GETLK, ALLOW),
JEQ32(F_SETLK, ALLOW),
JEQ32(F_SETLKW, ALLOW),
JEQ32(F_DUPFD, ALLOW),
JEQ32(F_DUPFD_CLOEXEC, ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowFork() {
return AllowSyscalls({
#ifdef __NR_fork
__NR_fork,
#endif
#ifdef __NR_vfork
__NR_vfork,
#endif
__NR_clone});
}
PolicyBuilder& PolicyBuilder::AllowWait() {
return AllowSyscalls({
#ifdef __NR_waitpid
__NR_waitpid,
#endif
__NR_wait4});
}
PolicyBuilder& PolicyBuilder::AllowHandleSignals() {
return AllowSyscalls({
__NR_rt_sigaction,
__NR_rt_sigreturn,
__NR_rt_sigprocmask,
#ifdef __NR_signal
__NR_signal,
#endif
#ifdef __NR_sigaction
__NR_sigaction,
#endif
#ifdef __NR_sigreturn
__NR_sigreturn,
#endif
#ifdef __NR_sigprocmask
__NR_sigprocmask,
#endif
#ifdef __NR_sigaltstack
__NR_sigaltstack,
#endif
});
}
PolicyBuilder& PolicyBuilder::AllowTCGETS() {
return AddPolicyOnSyscall(__NR_ioctl, {
ARG_32(1),
JEQ32(TCGETS, ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowTime() {
return AllowSyscalls({
#ifdef __NR_time
__NR_time,
#endif
__NR_gettimeofday, __NR_clock_gettime});
}
PolicyBuilder& PolicyBuilder::AllowSleep() {
return AllowSyscalls({
__NR_clock_nanosleep,
__NR_nanosleep,
});
}
PolicyBuilder& PolicyBuilder::AllowGetIDs() {
return AllowSyscalls({
__NR_getuid,
__NR_geteuid,
__NR_getresuid,
__NR_getgid,
__NR_getegid,
__NR_getresgid,
#ifdef __NR_getuid32
__NR_getuid32,
__NR_geteuid32,
__NR_getresuid32,
__NR_getgid32,
__NR_getegid32,
__NR_getresgid32,
#endif
__NR_getgroups,
});
}
PolicyBuilder& PolicyBuilder::AllowRestartableSequencesWithProcFiles(
CpuFenceMode cpu_fence_mode) {
AllowRestartableSequences(cpu_fence_mode);
AddFile("/proc/cpuinfo");
AddFile("/proc/stat");
if (cpu_fence_mode == kAllowSlowFences) {
AddFile("/proc/self/cpuset");
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowRestartableSequences(
CpuFenceMode cpu_fence_mode) {
#ifdef __NR_rseq
AllowSyscall(__NR_rseq);
#endif
AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(2), // prot
JNE32(PROT_READ | PROT_WRITE, JUMP(&labels, mmap_end)),
ARG_32(3), // flags
JNE32(MAP_PRIVATE | MAP_ANONYMOUS, JUMP(&labels, mmap_end)),
ALLOW,
LABEL(&labels, mmap_end),
};
});
AllowSyscall(__NR_getcpu);
AllowSyscall(__NR_membarrier);
AllowFutexOp(FUTEX_WAIT);
AllowFutexOp(FUTEX_WAKE);
AddPolicyOnSyscall(__NR_rt_sigprocmask, {
ARG_32(0),
JEQ32(SIG_SETMASK, ALLOW),
});
if (cpu_fence_mode == kAllowSlowFences) {
AllowSyscall(__NR_sched_getaffinity);
AllowSyscall(__NR_sched_setaffinity);
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowGetPIDs() {
return AllowSyscalls({
__NR_getpid,
__NR_getppid,
__NR_gettid,
});
}
PolicyBuilder& PolicyBuilder::AllowGetRlimit() {
return AllowSyscalls({
#ifdef __NR_getrlimit
__NR_getrlimit,
#endif
#ifdef __NR_ugetrlimit
__NR_ugetrlimit,
#endif
});
}
PolicyBuilder& PolicyBuilder::AllowSetRlimit() {
return AllowSyscalls({
#ifdef __NR_setrlimit
__NR_setrlimit,
#endif
#ifdef __NR_usetrlimit
__NR_usetrlimit,
#endif
});
}
PolicyBuilder& PolicyBuilder::AllowGetRandom() {
return AddPolicyOnSyscall(__NR_getrandom, {
ARG_32(2),
JEQ32(0, ALLOW),
JEQ32(GRND_NONBLOCK, ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowWipeOnFork() {
// System headers may not be recent enough to include MADV_WIPEONFORK.
static constexpr uint32_t kMadv_WipeOnFork = 18;
// The -1 value is used by code to probe that the kernel returns -EINVAL for
// unknown values because some environments, like qemu, ignore madvise
// completely, but code needs to know whether WIPEONFORK took effect.
return AddPolicyOnSyscall(__NR_madvise,
{
ARG_32(2),
JEQ32(kMadv_WipeOnFork, ALLOW),
JEQ32(static_cast<uint32_t>(-1), ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowLogForwarding() {
AllowWrite();
AllowSystemMalloc();
AllowTcMalloc();
// From comms
AllowGetPIDs();
AllowSyscalls({// from logging code
__NR_clock_gettime,
// From comms
__NR_gettid, __NR_close});
// For generating stacktraces in logging (e.g. `LOG(FATAL)`)
AddPolicyOnSyscall(__NR_rt_sigprocmask, {
ARG_32(0),
JEQ32(SIG_BLOCK, ALLOW),
});
AllowSyscall(__NR_prlimit64);
// For LOG(FATAL)
return AddPolicyOnSyscall(__NR_kill,
[](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(0),
JNE32(0, JUMP(&labels, pid_not_null)),
ARG_32(1),
JEQ32(SIGABRT, ALLOW),
LABEL(&labels, pid_not_null),
};
});
}
PolicyBuilder& PolicyBuilder::AllowUnlink() {
AllowSyscalls({
#ifdef __NR_unlink
__NR_unlink,
#endif
__NR_unlinkat,
});
return *this;
}
PolicyBuilder& PolicyBuilder::AllowRename() {
AllowSyscalls({
#ifdef __NR_rename
__NR_rename,
#endif
__NR_renameat,
#ifdef __NR_renameat2
__NR_renameat2,
#endif
});
return *this;
}
PolicyBuilder& PolicyBuilder::AllowFutexOp(int op) {
return AddPolicyOnSyscall(
__NR_futex, {
ARG_32(1),
// a <- a & FUTEX_CMD_MASK
BPF_STMT(BPF_ALU + BPF_AND + BPF_K,
static_cast<uint32_t>(FUTEX_CMD_MASK)),
JEQ32(static_cast<uint32_t>(op) & FUTEX_CMD_MASK, ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowStaticStartup() {
AllowGetRlimit();
AllowSyscalls({
// These syscalls take a pointer, so no restriction.
__NR_uname, __NR_brk, __NR_set_tid_address,
#if defined(__ARM_NR_set_tls)
// libc sets the TLS during startup
__ARM_NR_set_tls,
#endif
// This syscall takes a pointer and a length.
// We could restrict length, but it might change, so not worth it.
__NR_set_robust_list,
});
AllowFutexOp(FUTEX_WAIT_BITSET);
AddPolicyOnSyscall(__NR_rt_sigaction,
{
ARG_32(0),
// This is real-time signals used internally by libc.
JEQ32(__SIGRTMIN + 0, ALLOW),
JEQ32(__SIGRTMIN + 1, ALLOW),
});
AllowSyscall(__NR_rt_sigprocmask);
#ifdef SAPI_X86_64
// The second argument is a pointer.
AddPolicyOnSyscall(__NR_arch_prctl, {
ARG_32(0),
JEQ32(ARCH_SET_FS, ALLOW),
});
#endif
if constexpr (sapi::host_cpu::IsArm64()) {
BlockSyscallWithErrno(__NR_readlinkat, ENOENT);
}
#ifdef __NR_readlink
BlockSyscallWithErrno(__NR_readlink, ENOENT);
#endif
AddPolicyOnSyscall(__NR_mprotect, {
ARG_32(2),
JEQ32(PROT_READ, ALLOW),
});
return *this;
}
PolicyBuilder& PolicyBuilder::AllowDynamicStartup() {
AllowRead();
AllowStat();
AllowSyscalls({__NR_lseek,
#ifdef __NR__llseek
__NR__llseek, // Newer glibc on PPC
#endif
__NR_close, __NR_munmap});
AddPolicyOnSyscall(__NR_mprotect, {
ARG_32(2),
JEQ32(PROT_READ, ALLOW),
JEQ32(PROT_NONE, ALLOW),
JEQ32(PROT_READ | PROT_WRITE, ALLOW),
JEQ32(PROT_READ | PROT_EXEC, ALLOW),
});
AllowStaticStartup();
return AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(2), // prot
JEQ32(PROT_READ | PROT_EXEC, JUMP(&labels, prot_exec)),
JEQ32(PROT_READ | PROT_WRITE, JUMP(&labels, prot_read_write)),
JNE32(PROT_READ, JUMP(&labels, mmap_end)),
// PROT_READ
ARG_32(3), // flags
JEQ32(MAP_PRIVATE, ALLOW),
JUMP(&labels, mmap_end),
// PROT_READ | PROT_WRITE
LABEL(&labels, prot_read_write),
ARG_32(3), // flags
JEQ32(MAP_FILE | MAP_PRIVATE | MAP_FIXED | MAP_DENYWRITE, ALLOW),
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, ALLOW),
JEQ32(MAP_ANONYMOUS | MAP_PRIVATE, ALLOW),
JUMP(&labels, mmap_end),
// PROT_READ | PROT_EXEC
LABEL(&labels, prot_exec),
ARG_32(3), // flags
JEQ32(MAP_FILE | MAP_PRIVATE | MAP_DENYWRITE, ALLOW),
LABEL(&labels, mmap_end),
};
});
}
PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(
uint32_t num, absl::Span<const sock_filter> policy) {
return AddPolicyOnSyscalls({num}, policy);
}
PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(uint32_t num, BpfFunc f) {
return AddPolicyOnSyscalls({num}, f);
}
PolicyBuilder& PolicyBuilder::AddPolicyOnSyscalls(
absl::Span<const uint32_t> nums, absl::Span<const sock_filter> policy) {
std::deque<sock_filter> out;
// Insert and verify the policy.
out.insert(out.end(), policy.begin(), policy.end());
for (size_t i = 0; i < out.size(); ++i) {
sock_filter& filter = out[i];
const size_t max_jump = out.size() - i - 1;
if (!CheckBpfBounds(filter, max_jump)) {
SetError(absl::InvalidArgumentError("bpf jump out of bounds"));
return *this;
}
// Syscall arch is expected as TRACE value
if (filter.code == (BPF_RET | BPF_K) &&
(filter.k & SECCOMP_RET_ACTION) == SECCOMP_RET_TRACE &&
(filter.k & SECCOMP_RET_DATA) != Syscall::GetHostArch()) {
LOG(WARNING) << "SANDBOX2_TRACE should be used in policy instead of "
"TRACE(value)";
filter = SANDBOX2_TRACE;
}
}
// Pre-/Postcondition: Syscall number loaded into A register
out.push_back(LOAD_SYSCALL_NR);
if (out.size() > std::numeric_limits<uint32_t>::max()) {
SetError(absl::InvalidArgumentError("syscall policy is too long"));
return *this;
}
// Create jumps for each syscall.
size_t do_policy_loc = out.size();
// Iterate in reverse order and prepend instruction, so that jumps can be
// calculated easily.
constexpr size_t kMaxShortJump = 255;
bool last = true;
for (auto it = std::rbegin(nums); it != std::rend(nums); ++it) {
// If syscall is not matched try with the next one.
uint8_t jf = 0;
// If last syscall on the list does not match skip the policy by jumping
// over it.
if (last) {
if (out.size() > kMaxShortJump) {
out.push_front(
BPF_STMT(BPF_JMP + BPF_JA, static_cast<uint32_t>(out.size())));
} else {
jf = out.size();
}
last = false;
}
// Add a helper absolute jump if needed - the policy/last helper jump is
// out of reach of a short jump.
if ((out.size() - do_policy_loc) > kMaxShortJump) {
out.push_front(BPF_STMT(
BPF_JMP + BPF_JA, static_cast<uint32_t>(out.size() - policy.size())));
do_policy_loc = out.size();
++jf;
}
uint8_t jt = out.size() - do_policy_loc;
out.push_front(BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, *it, jt, jf));
}
user_policy_.insert(user_policy_.end(), out.begin(), out.end());
return *this;
}
PolicyBuilder& PolicyBuilder::AddPolicyOnSyscalls(
absl::Span<const uint32_t> nums, BpfFunc f) {
return AddPolicyOnSyscalls(nums, ResolveBpfFunc(f));
}
PolicyBuilder& PolicyBuilder::AddPolicyOnMmap(
absl::Span<const sock_filter> policy) {
return AddPolicyOnSyscalls(kMmapSyscalls, policy);
}
PolicyBuilder& PolicyBuilder::AddPolicyOnMmap(BpfFunc f) {
return AddPolicyOnSyscalls(kMmapSyscalls, f);
}
PolicyBuilder& PolicyBuilder::DangerDefaultAllowAll() {
user_policy_.push_back(ALLOW);
return *this;
}
absl::StatusOr<std::string> PolicyBuilder::ValidateAbsolutePath(
absl::string_view path) {
if (!file::IsAbsolutePath(path)) {
return absl::InvalidArgumentError(
absl::StrCat("Path is not absolute: '", path, "'"));
}
return ValidatePath(path);
}
absl::StatusOr<std::string> PolicyBuilder::ValidatePath(
absl::string_view path) {
std::string fixed_path = file::CleanPath(path);
if (fixed_path != path) {
return absl::InvalidArgumentError(absl::StrCat(
"Path was not normalized. '", path, "' != '", fixed_path, "'"));
}
return fixed_path;
}
std::vector<sock_filter> PolicyBuilder::ResolveBpfFunc(BpfFunc f) {
bpf_labels l = {0};
std::vector<sock_filter> policy = f(l);
if (bpf_resolve_jumps(&l, policy.data(), policy.size()) != 0) {
SetError(absl::InternalError("Cannot resolve bpf jumps"));
}
return policy;
}
absl::StatusOr<std::unique_ptr<Policy>> PolicyBuilder::TryBuild() {
auto output = absl::WrapUnique(new Policy());
if (user_policy_.size() > kMaxUserPolicyLength) {
return absl::FailedPreconditionError(
absl::StrCat("User syscall policy is to long (", user_policy_.size(),
" > ", kMaxUserPolicyLength, ")."));
}
if (!last_status_.ok()) {
return last_status_;
}
if (already_built_) {
return absl::FailedPreconditionError("Can only build policy once.");
}
if (use_namespaces_) {
if (allow_unrestricted_networking_ && hostname_ != kDefaultHostname) {
return absl::FailedPreconditionError(
"Cannot set hostname without network namespaces.");
}
output->SetNamespace(absl::make_unique<Namespace>(
allow_unrestricted_networking_, std::move(mounts_), hostname_));
} else {
// Not explicitly disabling them here as this is a technical limitation in
// our stack trace collection functionality.
LOG(WARNING) << "Using policy without namespaces, disabling stack traces on"
<< " crash";
}
output->collect_stacktrace_on_signal_ = collect_stacktrace_on_signal_;
output->collect_stacktrace_on_violation_ = collect_stacktrace_on_violation_;
output->collect_stacktrace_on_timeout_ = collect_stacktrace_on_timeout_;
output->collect_stacktrace_on_kill_ = collect_stacktrace_on_kill_;
output->collect_stacktrace_on_exit_ = collect_stacktrace_on_exit_;
output->user_policy_ = std::move(user_policy_);
output->user_policy_handles_bpf_ = user_policy_handles_bpf_;
auto pb_description = absl::make_unique<PolicyBuilderDescription>();
StoreDescription(pb_description.get());
output->policy_builder_description_ = std::move(pb_description);
output->allowed_hosts_ = std::move(allowed_hosts_);
already_built_ = true;
return std::move(output);
}
PolicyBuilder& PolicyBuilder::AddFile(absl::string_view path, bool is_ro) {
return AddFileAt(path, path, is_ro);
}
PolicyBuilder& PolicyBuilder::AddFileAt(absl::string_view outside,
absl::string_view inside, bool is_ro) {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
auto valid_outside = ValidateAbsolutePath(outside);
if (!valid_outside.ok()) {
SetError(valid_outside.status());
return *this;
}
if (absl::StartsWith(*valid_outside, "/proc/self") &&
*valid_outside != "/proc/self/cpuset") {
SetError(absl::InvalidArgumentError(
absl::StrCat("Cannot add /proc/self mounts, you need to mount the "
"whole /proc instead. You tried to mount ",
outside)));
return *this;
}
if (auto status = mounts_.AddFileAt(*valid_outside, inside, is_ro);
!status.ok()) {
SetError(
absl::InternalError(absl::StrCat("Could not add file ", outside, " => ",
inside, ": ", status.message())));
}
return *this;
}
PolicyBuilder& PolicyBuilder::AddLibrariesForBinary(
absl::string_view path, absl::string_view ld_library_path) {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
auto valid_path = ValidatePath(path);
if (!valid_path.ok()) {
SetError(valid_path.status());
return *this;
}
if (auto status = mounts_.AddMappingsForBinary(*valid_path, ld_library_path);
!status.ok()) {
SetError(absl::InternalError(absl::StrCat(
"Could not add libraries for ", *valid_path, ": ", status.message())));
}
return *this;
}
PolicyBuilder& PolicyBuilder::AddLibrariesForBinary(
int fd, absl::string_view ld_library_path) {
return AddLibrariesForBinary(absl::StrCat("/proc/self/fd/", fd),
ld_library_path);
}
PolicyBuilder& PolicyBuilder::AddDirectory(absl::string_view path, bool is_ro) {
return AddDirectoryAt(path, path, is_ro);
}
PolicyBuilder& PolicyBuilder::AddDirectoryAt(absl::string_view outside,
absl::string_view inside,
bool is_ro) {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
auto valid_outside = ValidateAbsolutePath(outside);
if (!valid_outside.ok()) {
SetError(valid_outside.status());
return *this;
}
if (absl::StartsWith(*valid_outside, "/proc/self")) {
SetError(absl::InvalidArgumentError(
absl::StrCat("Cannot add /proc/self mounts, you need to mount the "
"whole /proc instead. You tried to mount ",
outside)));
return *this;
}
if (absl::Status status =
mounts_.AddDirectoryAt(*valid_outside, inside, is_ro);
!status.ok()) {
SetError(absl::InternalError(absl::StrCat("Could not add directory ",
outside, " => ", inside, ": ",
status.message())));
return *this;
}
return *this;
}
PolicyBuilder& PolicyBuilder::AddTmpfs(absl::string_view inside, size_t size) {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
if (auto status = mounts_.AddTmpfs(inside, size); !status.ok()) {
SetError(absl::InternalError(absl::StrCat("Could not mount tmpfs ", inside,
": ", status.message())));
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowUnrestrictedNetworking() {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
allow_unrestricted_networking_ = true;
return *this;
}
PolicyBuilder& PolicyBuilder::SetHostname(absl::string_view hostname) {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
hostname_ = std::string(hostname);
return *this;
}
PolicyBuilder& PolicyBuilder::CollectStacktracesOnViolation(bool enable) {
collect_stacktrace_on_violation_ = enable;
return *this;
}
PolicyBuilder& PolicyBuilder::CollectStacktracesOnSignal(bool enable) {
collect_stacktrace_on_signal_ = enable;
return *this;
}
PolicyBuilder& PolicyBuilder::CollectStacktracesOnTimeout(bool enable) {
collect_stacktrace_on_timeout_ = enable;
return *this;
}
PolicyBuilder& PolicyBuilder::CollectStacktracesOnKill(bool enable) {
collect_stacktrace_on_kill_ = enable;
return *this;
}
PolicyBuilder& PolicyBuilder::CollectStacktracesOnExit(bool enable) {
collect_stacktrace_on_exit_ = enable;
return *this;
}
PolicyBuilder& PolicyBuilder::AddNetworkProxyPolicy() {
if (allowed_hosts_) {
SetError(absl::FailedPreconditionError(
"AddNetworkProxyPolicy or AddNetworkProxyHandlerPolicy can be called "
"at most once"));
return *this;
}
allowed_hosts_ = AllowedHosts();
AllowFutexOp(FUTEX_WAKE);
AllowFutexOp(FUTEX_WAIT);
AllowFutexOp(FUTEX_WAIT_BITSET);
AllowSyscalls({
#ifdef __NR_dup2
__NR_dup2,
#endif
__NR_recvmsg,
__NR_close,
__NR_gettid,
});
AddPolicyOnSyscall(__NR_socket, {
ARG_32(0),
JEQ32(AF_INET, ALLOW),
JEQ32(AF_INET6, ALLOW),
});
AddPolicyOnSyscall(__NR_getsockopt,
[](bpf_labels& labels) -> std::vector<sock_filter> {
return {
ARG_32(1),
JNE32(SOL_SOCKET, JUMP(&labels, getsockopt_end)),
ARG_32(2),
JEQ32(SO_TYPE, ALLOW),
LABEL(&labels, getsockopt_end),
};
});
#ifdef SAPI_PPC64_LE
AddPolicyOnSyscall(__NR_socketcall, {
ARG_32(0),
JEQ32(SYS_SOCKET, ALLOW),
JEQ32(SYS_GETSOCKOPT, ALLOW),
JEQ32(SYS_RECVMSG, ALLOW),
});
#endif
return *this;
}
PolicyBuilder& PolicyBuilder::AddNetworkProxyHandlerPolicy() {
AddNetworkProxyPolicy();
AllowSyscall(__NR_rt_sigreturn);
AddPolicyOnSyscall(__NR_rt_sigaction, {
ARG_32(0),
JEQ32(SIGSYS, ALLOW),
});
AddPolicyOnSyscall(__NR_rt_sigprocmask, {
ARG_32(0),
JEQ32(SIG_UNBLOCK, ALLOW),
});
AddPolicyOnSyscall(__NR_connect, {TRAP(0)});
#ifdef SAPI_PPC64_LE
AddPolicyOnSyscall(__NR_socketcall, {
ARG_32(0),
JEQ32(SYS_CONNECT, TRAP(0)),
});
#endif
return *this;
}
PolicyBuilder& PolicyBuilder::SetRootWritable() {
EnableNamespaces(); // NOLINT(clang-diagnostic-deprecated-declarations)
mounts_.SetRootWritable();
return *this;
}
void PolicyBuilder::StoreDescription(PolicyBuilderDescription* pb_description) {
for (const auto& handled_syscall : handled_syscalls_) {
pb_description->add_handled_syscalls(handled_syscall);
}
}
PolicyBuilder& PolicyBuilder::AllowIPv4(const std::string& ip_and_mask,
uint32_t port) {
if (!allowed_hosts_) {
SetError(absl::FailedPreconditionError(
"AddNetworkProxyPolicy or AddNetworkProxyHandlerPolicy must be called "
"before adding IP rules"));
return *this;
}
absl::Status status = allowed_hosts_->AllowIPv4(ip_and_mask, port);
if (!status.ok()) {
SetError(status);
}
return *this;
}
PolicyBuilder& PolicyBuilder::AllowIPv6(const std::string& ip_and_mask,
uint32_t port) {
if (!allowed_hosts_) {
SetError(absl::FailedPreconditionError(
"AddNetworkProxyPolicy or AddNetworkProxyHandlerPolicy must be called "
"before adding IP rules"));
return *this;
}
absl::Status status = allowed_hosts_->AllowIPv6(ip_and_mask, port);
if (!status.ok()) {
SetError(status);
}
return *this;
}
PolicyBuilder& PolicyBuilder::SetError(const absl::Status& status) {
LOG(ERROR) << status;
last_status_ = status;
return *this;
}
} // namespace sandbox2
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