Future Work: __mwrite()

• on OpenBSD, the GOT and/or PLT indirection tables for dynamic linking are read-only to block a class of attacks

• when a (lazy) binding needs to be updated, ld.so uses mprotect() to make it writable, does the update, then protects it again

        sigprocmask(SIG_BLOCK, &allsigs, &curset);
        spinlock_lock(&bind_lock);              /* libpthread cb */
        mprotect(addr, len, PROT_READ|PROT_WRITE);
        /* update the GOT entry */
        mprotect(addr, len, PROT_READ);
        spinlock_unlock(&bind_lock);            /* libpthread cb */
        sigprocmask(SIG_SETMASK, &curset, NULL);

• mprotect() involves TLB flushing in many cases

• for short lived processes, most their syscalls may be sigprocmask() and mprotect(): 434 of 523 for w