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

[Linus Torvalds]

On Wed, May 13, 2020 at 6:00 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> > But we should likely at least disallow it entirely on platforms where
> > we really can't - or pick one hardcoded choice. On sparc, you really
> > _have_ to specify one or the other.
>
> OK. BTW, is there any way to detect the kernel/user space overlap on
> memory layout statically? If there, I can do it. (I don't like
> "if (CONFIG_X86)" thing....)
> Or, maybe we need CONFIG_ARCH_OVERLAP_ADDRESS_SPACE?

I think it would be better to have a CONFIG variable that
architectures can just 'select' to show that they are ok with separate
kernel and user addresses.

Because I don't think we have any way to say that right now as-is. You
can probably come up with hacky ways to approximate it, ie something
like

    if (TASK_SIZE_MAX > PAGE_OFFSET)
        .... they overlap ..

which would almost work, but..

                 Linus