test(libc): guard timingsafe comparison values and read extents

core/libs/prx/libc/CMakeLists.txt

@@ -482,6 +482,16 @@ if(BUILD_TESTING)
         set_tests_properties(guest_bounds_checking PROPERTIES ENVIRONMENT_MODIFICATION
             "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
     endif()
+    add_test_executable(guest_timingsafe_boundary_tests ${LIBS_INCLUDE_DIR}/tests/GuestTimingsafeBoundary.cpp)
+    target_include_directories(guest_timingsafe_boundary_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(guest_timingsafe_boundary_tests PRIVATE libc)
+    configure_windows_unwind(guest_timingsafe_boundary_tests)
+    add_test(NAME guest_timingsafe_boundary COMMAND guest_timingsafe_boundary_tests)
+    set_tests_properties(guest_timingsafe_boundary PROPERTIES TIMEOUT 20)
+    if(WIN32)
+        set_tests_properties(guest_timingsafe_boundary PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
+    endif()
     add_test_executable(guest_zero_runs_tests ${LIBS_INCLUDE_DIR}/tests/GuestZeroRuns.cpp)
     target_include_directories(guest_zero_runs_tests PRIVATE ${LIBS_INCLUDE_DIR})
     target_link_libraries(guest_zero_runs_tests PRIVATE libc)

core/libs/tests/GuestTimingsafeBoundary.cpp

@@ -0,0 +1,88 @@
+#include "prx/libc/include/Api.hpp"
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <vector>
+
+static void Require(bool condition) {
+    if (!condition) {
+        std::fputs("GuestTimingsafeBoundary check failed\n", stderr);
+        std::abort();
+    }
+}
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <sys/mman.h>
+#include <unistd.h>
+#endif
+
+class Buffer {
+    unsigned char* allocation;
+    std::size_t page;
+public:
+    Buffer() {
+#ifdef _WIN32
+        SYSTEM_INFO info{};
+        GetSystemInfo(&info);
+        page = info.dwPageSize;
+        allocation = static_cast<unsigned char*>(VirtualAlloc(nullptr, page * 3, MEM_RESERVE | MEM_COMMIT, PAGE_NOACCESS));
+        Require(allocation != nullptr);
+        DWORD previous;
+        Require(VirtualProtect(allocation + page, page, PAGE_READWRITE, &previous) != 0);
+#else
+        const long size = sysconf(_SC_PAGESIZE);
+        Require(size > 0);
+        page = static_cast<std::size_t>(size);
+        allocation = static_cast<unsigned char*>(mmap(nullptr, page * 3, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
+        Require(allocation != MAP_FAILED);
+        Require(mprotect(allocation + page, page, PROT_READ | PROT_WRITE) == 0);
+#endif
+        std::memset(allocation + page, 0xa5, page);
+    }
+    ~Buffer() {
+#ifdef _WIN32
+        Require(VirtualFree(allocation, 0, MEM_RELEASE) != 0);
+#else
+        Require(munmap(allocation, page * 3) == 0);
+#endif
+    }
+    Buffer(const Buffer&) = delete;
+    Buffer& operator=(const Buffer&) = delete;
+    template<class T = unsigned char>
+    T* At(std::size_t count) {
+        Require(count <= (page - 32) / sizeof(T));
+        return reinterpret_cast<T*>(allocation + page * 2 - (std::max)(count, std::size_t{1}) * sizeof(T));
+    }
+};
+
+static int Sign(int value) {
+    return (value > 0) - (value < 0);
+}
+
+int main() {
+    Buffer first, second;
+    for (std::size_t length = 0; length <= 128; ++length) {
+        auto* left = first.At(length);
+        auto* right = second.At(length);
+        const auto extent = (std::max)(length, std::size_t{1});
+        for (int mode = 0; mode < 4; ++mode) {
+            for (std::size_t i = 0; i < extent; ++i) left[i] = right[i] = static_cast<unsigned char>(i * 131 + length);
+            if (length && mode < 3) {
+                const auto position = mode == 0 ? 0 : mode == 1 ? length / 2 : length - 1;
+                left[position] = 0xff; right[position] = 1;
+                if (position + 1 < length) { left[position + 1] = 1; right[position + 1] = 0xff; }
+            }
+            int expected = 0;
+            for (std::size_t i = 0; i < length; ++i) if (left[i] != right[i]) { expected = left[i] > right[i] ? 1 : -1; break; }
+            const std::vector<unsigned char> a(left, left + extent), b(right, right + extent);
+            Require(Sign(timingsafe_memcmp_nid_postfix(left, right, length)) == expected);
+            Require(Sign(timingsafe_memcmp_nid_postfix(right, left, length)) == -expected);
+            Require(std::equal(a.begin(), a.end(), left) && std::equal(b.begin(), b.end(), right));
+        }
+    }
+}