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

[Daniel Borkmann]

On 5/14/20 11:44 AM, Masami Hiramatsu wrote:
> On Wed, 13 May 2020 19:43:24 -0700
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > 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..
>
> It seems TASK_SIZE_MAX is defined only on x86 and s390, what about
> comparing STACK_TOP_MAX with PAGE_OFFSET ?
> Anyway, I agree that the best way is introducing a CONFIG.

Agree, CONFIG knob that archs can select feels cleanest. Fwiw, I've cooked
up fixes for bpf side locally here and finishing up testing, will push out
later today.

Thanks,
Daniel