Simplify ptrace emulation and code style fixes
PiperOrigin-RevId: 369862187
Change-Id: Ia0759c320cde1c9e3798f0df5c2a0d50ca20fd71
diff --git a/sandboxed_api/sandbox2/unwind/BUILD.bazel b/sandboxed_api/sandbox2/unwind/BUILD.bazel
index 9ac2e1e..a6c1707 100644
--- a/sandboxed_api/sandbox2/unwind/BUILD.bazel
+++ b/sandboxed_api/sandbox2/unwind/BUILD.bazel
@@ -27,6 +27,7 @@
hdrs = ["ptrace_hook.h"],
copts = sapi_platform_copts(),
visibility = ["@org_gnu_libunwind//:__subpackages__"],
+ deps = ["@com_google_absl//absl/strings"],
)
cc_library(
diff --git a/sandboxed_api/sandbox2/unwind/CMakeLists.txt b/sandboxed_api/sandbox2/unwind/CMakeLists.txt
index 58ac1fc..9107ee0 100644
--- a/sandboxed_api/sandbox2/unwind/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/unwind/CMakeLists.txt
@@ -18,8 +18,9 @@
ptrace_hook.h
)
add_library(sandbox2::ptrace_hook ALIAS sandbox2_ptrace_hook)
-target_link_libraries(sandbox2_ptrace_hook PRIVATE
- sapi::base
+target_link_libraries(sandbox2_ptrace_hook
+ PRIVATE sapi::base
+ PUBLIC absl::strings
)
# sandboxed_api/sandbox2/unwind:unwind
diff --git a/sandboxed_api/sandbox2/unwind/ptrace_hook.cc b/sandboxed_api/sandbox2/unwind/ptrace_hook.cc
index 4a79d22..e9bc80b 100644
--- a/sandboxed_api/sandbox2/unwind/ptrace_hook.cc
+++ b/sandboxed_api/sandbox2/unwind/ptrace_hook.cc
@@ -21,80 +21,75 @@
#include <cstdint>
#include <cstdio>
#include <cstring>
+#include <vector>
-// Maximum register struct size: 128 u64.
-constexpr size_t kRegisterBufferSize = 128 * 8;
-// Contains the register values in a ptrace specified format.
-// This format is pretty opaque which is why we just forward
-// the raw bytes (up to a certain limit).
-static unsigned char register_values[kRegisterBufferSize];
-static size_t n_register_values_bytes_used = 0;
+namespace sandbox2 {
+namespace {
-// It should not be necessary to put this in a thread local storage as we
-// do not support setting up the forkserver when there is more than one thread.
-// However there might be some edge-cases, so we do this just in case.
-thread_local bool emulate_ptrace = false;
+// Register size is `long` for the supported architectures according to the
+// kernel.
+using RegType = long; // NOLINT
+constexpr size_t kRegSize = sizeof(RegType);
-void ArmPtraceEmulation() { emulate_ptrace = true; }
+// Contains the register values in a ptrace specified format. This format is
+// pretty opaque which is why we just forward the raw bytes (up to a certain
+// limit).
+auto* g_registers = new std::vector<RegType>();
-void InstallUserRegs(const char *ptr, size_t size) {
- if (sizeof(register_values) < size) {
- fprintf(stderr, "install_user_regs: Got more bytes than supported (%lu)\n",
- size);
- } else {
- memcpy(®ister_values, ptr, size);
- n_register_values_bytes_used = size;
- }
+// Whether ptrace() emulation is in effect. This can only be enabled (per
+// thread), never disabled.
+thread_local bool g_emulate_ptrace = false;
+
+} // namespace
+
+void EnablePtraceEmulationWithUserRegs(absl::string_view regs) {
+ g_registers->resize((regs.size() + 1) / kRegSize);
+ memcpy(&g_registers->front(), regs.data(), regs.size());
+ g_emulate_ptrace = true;
}
// Replaces the libc version of ptrace.
// This wrapper makes use of process_vm_readv to read process memory instead of
// issuing ptrace syscalls. Accesses to registers will be emulated, for this the
-// register values should be set via install_user_regs().
-// The emulation can be switched on using arm_ptrace_emulation().
+// register values should be set via EnablePtraceEmulationWithUserRegs().
extern "C" long int ptrace_wrapped( // NOLINT
- enum __ptrace_request request, pid_t pid, void *addr, void *data) {
- // Register size is `long` for the supported architectures according to the
- // kernel.
- using reg_type = long; // NOLINT
- constexpr size_t reg_size = sizeof(reg_type);
- if (!emulate_ptrace) {
+ enum __ptrace_request request, pid_t pid, void* addr, void* data) {
+ if (!g_emulate_ptrace) {
return ptrace(request, pid, addr, data);
}
+
switch (request) {
case PTRACE_PEEKDATA: {
long int read_data; // NOLINT
+ struct iovec local = {
+ .iov_base = &read_data,
+ .iov_len = sizeof(long int), // NOLINT
+ };
+ struct iovec remote = {
+ .iov_base = addr,
+ .iov_len = sizeof(long int), // NOLINT
+ };
- struct iovec local, remote;
- local.iov_len = sizeof(long int); // NOLINT
- local.iov_base = &read_data;
-
- remote.iov_len = sizeof(long int); // NOLINT
- remote.iov_base = addr;
-
- if (process_vm_readv(pid, &local, 1, &remote, 1, 0) > 0) {
- return read_data;
- } else {
+ if (process_vm_readv(pid, &local, 1, &remote, 1, 0) <= 0) {
return -1;
}
- } break;
- case PTRACE_PEEKUSER: {
- uintptr_t next_offset = reinterpret_cast<uintptr_t>(addr) + reg_size;
+ return read_data;
+ }
+ case PTRACE_PEEKUSER:
// Make sure read is in-bounds and aligned.
- if (next_offset <= n_register_values_bytes_used &&
- reinterpret_cast<uintptr_t>(addr) % reg_size == 0) {
- return reinterpret_cast<reg_type *>(
- ®ister_values)[reinterpret_cast<uintptr_t>(addr) / reg_size];
- } else {
+ if (uintptr_t offset = reinterpret_cast<uintptr_t>(addr);
+ offset + kRegSize > g_registers->size() * kRegSize ||
+ offset % kRegSize != 0) {
return -1;
+ } else {
+ return (*g_registers)[offset / kRegSize];
}
- } break;
- default: {
- fprintf(stderr, "ptrace-wrapper: forbidden operation invoked: %d\n",
+ default:
+ fprintf(stderr, "ptrace_wrapped(): operation not permitted: %d\n",
request);
_exit(1);
- }
}
-
return 0;
}
+
+} // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/unwind/ptrace_hook.h b/sandboxed_api/sandbox2/unwind/ptrace_hook.h
index 1ba1a6d..773d7ed 100644
--- a/sandboxed_api/sandbox2/unwind/ptrace_hook.h
+++ b/sandboxed_api/sandbox2/unwind/ptrace_hook.h
@@ -15,12 +15,13 @@
#ifndef SANDBOXED_API_SANDBOX2_UNWIND_PTRACE_HOOK_H_
#define SANDBOXED_API_SANDBOX2_UNWIND_PTRACE_HOOK_H_
-#include <cstddef>
+#include "absl/strings/string_view.h"
+
+namespace sandbox2 {
// Sets the register values that the ptrace emulation will return.
-void InstallUserRegs(const char* ptr, size_t size);
+void EnablePtraceEmulationWithUserRegs(absl::string_view regs);
-// Enables the ptrace emulation.
-void ArmPtraceEmulation();
+} // namespace sandbox2
#endif // SANDBOXED_API_SANDBOX2_UNWIND_PTRACE_HOOK_H_
diff --git a/sandboxed_api/sandbox2/unwind/unwind.cc b/sandboxed_api/sandbox2/unwind/unwind.cc
index a8b0a00..f5ae330 100644
--- a/sandboxed_api/sandbox2/unwind/unwind.cc
+++ b/sandboxed_api/sandbox2/unwind/unwind.cc
@@ -123,9 +123,7 @@
return false;
}
- const std::string& data = setup.regs();
- InstallUserRegs(data.c_str(), data.length());
- ArmPtraceEmulation();
+ EnablePtraceEmulationWithUserRegs(setup.regs());
std::vector<uintptr_t> ips;
std::vector<std::string> stack_trace =
