Re: [PATCH] m68k: Implement "current_stack_pointer"

[Geert Uytterhoeven]

On Thu, Feb 24, 2022 at 10:12 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
> From: Geert Uytterhoeven
> > Sent: 24 February 2022 08:59
> ...
> > > +register unsigned long current_stack_pointer __asm__("sp");
> >
> > I don't know what HARDENED_USERCOPY does, so I don't know if you need
> > "usp" (see rdusp()) or "sp"?
>
> HARDENED_USERCOPY significantly slows down some systems calls
> (especially things like sendmsg()) by trying to run-time verify
> that the kernel buffer doesn't overrun a stack frame or kmalloc()ed

Kernel stack frame of user stack frame?

> buffer.
>
> I've got measurable improvements by either using __copy_to/from_user()
> (which skips the tests) or user_access_begin() and __get_user().
>
> At the moment the code for reading a compat iovec[] is actually
> faster than that for a native one!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds