1. It wouldn't segfault, because it's the kernel reading the data. It can read from anywhere. 2. Kernel already checks, whether the buffer is in a mapped memor

1. It wouldn't segfault, because it's the kernel reading the data. It can read from anywhere. 2. Kernel already checks, whether the buffer is in a mapped memory region that your process has access to. If it isn't, the error is signaled with errno=EFAULT.