On Tue, Sep 01, 2020 at 03:02:08PM +0100, Mark Rutland wrote:
> d instead do user pointer
> > masking, throughout the x86 uaccess code. This is similar to what arm64
> > is already doing.
> >
> > barrier_nospec() is now unused, and can be removed.
>
> One thing to consider is whether you need a speculation barrier after
> set_fs(). Otherwise for code like:
>
> | fs = get_fs();
> | if (cond)
> | set_fs(KERNEL_DS);
> | copy_to_user(...)
> | set_fs(fs)
>
> ... the set_fs() can occur speculatively, and may be able to satisfy
> the masking logic if forwarded within the cpu.
>
> See arm64 commit:
>
> c2f0ad4fc089cff8 ("arm64: uaccess: Prevent speculative use of the current
> addr_limit")
Do you have any examples of that conditional set_fs(KERNEL_DS) pattern?
I wasn't able to find any.
--
Josh
