Re: [PATCH 11/18] maccess: remove strncpy_from_unsafe

[Linus Torvalds]

On Wed, May 13, 2020 at 3:36 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>
> It's used for both.

Daniel, BPF real;ly needs to make up its mind about that.

You *cannot* use ti for both.

Yes, it happens to work on x86 and some other architectures.

But on other architectures, the exact same pointer value can be a
kernel pointer or a user pointer.

> Given this is enabled on pretty much all program types, my
> assumption would be that usage is still more often on kernel memory than user one.

You need to pick one.

If you know it is a user pointer, use strncpy_from_user() (possibly
with disable_pagefault() aka strncpy_from_user_nofault()).

And if you know it is a kernel pointer, use strncpy_from_unsafe() (aka
strncpy_from_kernel_nofault()).

You really can't pick the "randomly one or the other guess what I mean " option.

                  Linus