Executing machine code in memory

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You need a page with write execute permissions. See mmap(2) and mprotect(2) if you are under unix. You shouldn’t do it using malloc.

Also, read what the others said, you can only run raw machine code using your loader. If you try to run an ELF header it will probably segfault all the same.

Regarding the content of replies and downmods:

1- OP said he was trying to run machine code, so I replied on that rather than executing an executable file.

2- See why you don’t mix malloc and mman functions:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/mman.h>

int main()
{
    char *a=malloc(10);
    char *b=malloc(10);
    char *c=malloc(10);
    memset (a,'a',4095);
    memset (b,'b',4095);
    memset (c,'c',4095);
    puts (a);
    memset (c,0xc3,10); /* return */

    /* c is not alligned to page boundary so this is NOOP.
     Many implementations include a header to malloc'ed data so it's always NOOP. */
    mprotect(c,10,PROT_READ|PROT_EXEC);
    b[0]='H'; /* oops it is still writeable. If you provided an alligned
    address it would segfault */
    char *d=mmap(0,4096,PROT_READ|PROT_WRITE|PROT_EXEC,MAP_PRIVATE|MAP_ANON,-1,0);
    memset (d,0xc3,4096);
    ((void(*)(void))d)();
    ((void(*)(void))c)(); /* oops it isn't executable */
    return 0;
}

It displays exactly this behavior on Linux x86_64 other ugly behavior sure to arise on other implementations.

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