Re: [PATCH v3 0/2] MR5222: kernelbase: Allow WriteProcessMemory to succeed on PAGE_EXECUTE_READ.

[Marc-Aurel Zent (＠mzent)]

On Tue Mar  5 16:46:12 2024 +0000, Marc-Aurel Zent wrote:
> No idea, I assume most of the initialized memory was 0 and some of the
> cache got invalidated when doing the syscall compared to the memcpy case.

This is the code I used to test that (quickly thrown together), maybe it tests differently on different machines, but I get perfect consistency with it for the results above.
```
#include <windows.h>
#include <cstdio>

typedef NTSTATUS(NTAPI* pNtWriteVirtualMemory)(
    HANDLE ProcessHandle,
    PVOID BaseAddress,
    VOID* Buffer,
    ULONG NumberOfBytesToWrite,
    PULONG NumberOfBytesWritten
    );

typedef int (*test_function)();

int main() {
    HMODULE ntdll = GetModuleHandleW(L"ntdll");
    pNtWriteVirtualMemory NtWriteVirtualMemory = (pNtWriteVirtualMemory)GetProcAddress(ntdll, "NtWriteVirtualMemory");

void* execMemory = VirtualAlloc(NULL, 4096, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);

unsigned char code[] = {
        // movz x0, #1, lsl #0
        0x01, 0x00, 0x80, 0xD2,
        // ret
        0xC0, 0x03, 0x5F, 0xD6
    };
    SIZE_T bytesWritten;
    ULONG bytesWritten2;

//memcpy(execMemory, code, sizeof(code));
    NtWriteVirtualMemory(GetCurrentProcess(), (char*)execMemory , code , sizeof(code), &bytesWritten2);
    //WriteProcessMemory(GetCurrentProcess(), (char*)execMemory, code, sizeof(code), &bytesWritten);

//FlushInstructionCache(GetCurrentProcess(), execMemory, sizeof(code));

test_function func = (test_function)execMemory;
    int result = func();
    printf("Function returned: %d\n", result);

VirtualFree(execMemory, 0, MEM_RELEASE);
    return 0;
}
```