c++中的Meltdown POC

Question

我听说了Meltdown漏洞并阅读了paper，这有点困难，因为我不是以英语为母语的人，但我决定做一个小的概念证明c++程序，如下所示，我想知道代码不工作的原因。我已经在AMD FX8350八核和英特尔I3处理器上进行了测试

/*In this code I wanted to make a PoC for the Meltdown flaw (https://meltdownattack.com/)*/
#include "stdafx.h"
#include <stdlib.h>
#include <iostream>
#include <chrono>

int secretvar = 15;     //This is our "unreadable" var wich we "cannot" read but we will have the value exposed via cache attack
int x = rand() % 100;   //Used later, importent that it's random

int main()
{   
    int arr[1000];                  //We setup our array
    for (int i = 0; i < 100; ++i) { //Fill it with random values
        arr[i] = rand() % 10 + 1;
    };

    if (x == 4) {                       //Here I want to trigger the Out-of-Order execution so that the cpu executes the code below th if case
        int c = arr[secretvar];         //before it really checks if x is actually 4. And with this, the CPU would put the cached variable "c" into
                                        //its cache.
    };

/*At this point we dont know th value of secretvar but we know that the CPU has cached some index with the
exact value of secretvar.Therefore we can now iterate over the array and how long it takes the cpu to acess the
diffrent array indexes.The cpu will be faster at acessing one specific element because it is taken from cache 
and not from the memory.This index is the value of secretvar.*/

    double lowest_val = 500;
    int    lowest_index = 0;

    for (int i = 0; i < 100; i++) {
        auto start = std::chrono::high_resolution_clock::now(); //start timer
        arr[i];                                                 //acess array
        auto finish = std::chrono::high_resolution_clock::now();//end timer
        std::chrono::duration<double> elapsed = finish - start;//calculate needed time
        double e = elapsed.count();
        if (e < lowest_val) {
            lowest_val = e;
            lowest_index = i;
        }
        std::cout << i << " : " << e << " s\n"; //show it to the screen
    }
    std::cout <<  lowest_index << "Was acessed fastest "<< " with a time of  "<< lowest_val << "ms" << std::endl;
    system("pause");
    return 0;
}

Answer 1

好的，所以我意识到如果我用汇编语言编程，这个测试会更准确。接下来我将尝试这样做，但在此之前，我必须学习一些东西。我认为这个问题已经回答了，但是仍然欢迎关于c++项目的建议。谢谢你的帮助