Dynamically finding sys_call_table on Linux x86_64 systems

gistfile1.c

void **find_sys_call_table(void *kernel_addr, int kernel_size)
{
    /*
        Check for the system_call_fastpath() signature, hand-written piece of
        assembly code from arch/x86/kernel/entry_64.S:

            ja      badsys
            mov     rcx, r10
            call    sys_call_table[rax * 8]
            mov     [rsp + 20h], rax
                    
        ret_from_sys_call:

            mov     edi, 1000FEFFh

        This instructions are unchanged for the last 7 years (and maybe even more, haven't 
        older kernels on my test machines), so, looks reliable enough.
    */
    unsigned char *mask = "\xff\xff\x00\x00\x00\x00"
                          "\xff\xff\xff"
                          "\xff\xff\xff\x00\x00\x00\x00"
                          "\xff\xff\xff\xff\xff"
                          "\xff\xff\xff\xff\xff";

    unsigned char *sign = "\x0f\x87\x00\x00\x00\x00"
                          "\x4c\x89\xd1"
                          "\xff\x14\xc5\x00\x00\x00\x00"
                          "\x48\x89\x44\x24\x20"
                          "\xbf\xff\xfe\x00\x10";

    int i = 0, n = 0, sign_len = 26;

    for (i = 0; i < kernel_size; i += 1)
    {
        unsigned char *p = (unsigned char *)kernel_addr + i;
        char matched = 1;

        for (n = 0; n < sign_len; n += 1)
        {
            // match signature byte
            if ((*(p + n) & mask[n]) != sign[n])
            {
                matched = 0;
                break;
            }
        }

        if (matched > 0)
        {
            // get sys_call_table address
            return (void **)(((unsigned long long)kernel_addr & 0xffffffff00000000) + *(unsigned long *)(p + 0x0c));
        }
    }

    return NULL;
}