Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths

[Linus Torvalds]

On Tue, Jan 16, 2018 at 8:30 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> I think the access_ok() conversion to return a speculation sanitized
> pointer or NULL is the way to go unless I'm missing something simpler.

No, that's way too big of a conversion.

Just make get_user() and friends (that currently use ASM_STAC) use the
address masking.

The people who use uaccess_begin() can use the lfence there.

Basically, the rule is trivial: find all 'stac' users, and use address
masking if those users already integrate the limit check, and lfence
they don't.

                Linus