115 lines
3.6 KiB
C++
115 lines
3.6 KiB
C++
// Copyright 2019 Google LLC
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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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// https://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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#include "sandboxed_api/sandbox2/unwind/ptrace_hook.h"
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#include <elf.h> // For NT_PRSTATUS
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#include <sys/ptrace.h>
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#include <sys/uio.h>
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#include <syscall.h>
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#include <unistd.h>
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#include <cstdint>
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#include <cstdio>
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#include <cstdlib>
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#include <cstring>
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#include <vector>
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#include "sandboxed_api/sandbox2/util/syscall_trap.h"
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// Android doesn't use an enum for __ptrace_request, use int instead.
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#if defined(__ANDROID__)
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using PtraceRequest = int;
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#else
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using PtraceRequest = __ptrace_request;
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#endif
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namespace sandbox2 {
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namespace {
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// Register size is `long` for the supported architectures according to the
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// kernel.
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using RegType = long; // NOLINT
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constexpr size_t kRegSize = sizeof(RegType);
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// Contains the register values in a ptrace specified format. This format is
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// pretty opaque which is why we just forward the raw bytes (up to a certain
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// limit).
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auto* g_registers = new std::vector<RegType>();
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// Hooks ptrace.
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// This wrapper makes use of process_vm_readv to read process memory instead of
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// issuing ptrace syscalls. Accesses to registers will be emulated, for this the
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// register values should be set via EnablePtraceEmulationWithUserRegs().
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long int ptrace_hook( // NOLINT
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PtraceRequest request, pid_t pid, void* addr, void* data) {
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switch (request) {
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case PTRACE_PEEKDATA: {
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RegType read_data;
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iovec local = {.iov_base = &read_data, .iov_len = sizeof(read_data)};
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iovec remote = {.iov_base = addr, .iov_len = sizeof(read_data)};
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if (process_vm_readv(pid, &local, 1, &remote, 1, 0) <= 0) {
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return -1;
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}
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*reinterpret_cast<RegType*>(data) = read_data;
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break;
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}
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case PTRACE_PEEKUSER: {
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// Make sure read is in-bounds and aligned.
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auto offset = reinterpret_cast<uintptr_t>(addr);
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if (offset + kRegSize > g_registers->size() * kRegSize ||
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offset % kRegSize != 0) {
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return -1;
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}
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*reinterpret_cast<RegType*>(data) = (*g_registers)[offset / kRegSize];
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break;
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}
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case PTRACE_GETREGSET: {
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// Only return general-purpose registers.
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if (auto kind = reinterpret_cast<uintptr_t>(addr); kind != NT_PRSTATUS) {
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return -1;
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}
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auto reg_set = reinterpret_cast<iovec*>(data);
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if (reg_set->iov_len > g_registers->size() * kRegSize) {
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return -1;
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}
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memcpy(reg_set->iov_base, g_registers->data(), reg_set->iov_len);
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break;
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}
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default:
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fprintf(stderr, "ptrace_hook(): operation not permitted: %d\n", request);
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abort();
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}
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return 0;
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}
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} // namespace
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void EnablePtraceEmulationWithUserRegs(absl::string_view regs) {
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g_registers->resize((regs.size() + 1) / kRegSize);
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memcpy(&g_registers->front(), regs.data(), regs.size());
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SyscallTrap::Install([](int nr, SyscallTrap::Args args, uintptr_t* rv) {
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if (nr != __NR_ptrace) {
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return false;
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}
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*rv = ptrace_hook(
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static_cast<PtraceRequest>(args[0]), static_cast<pid_t>(args[1]),
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reinterpret_cast<void*>(args[2]), reinterpret_cast<void*>(args[3]));
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return true;
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});
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}
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} // namespace sandbox2
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