Re: [patch 05/16] mm: Allow special mappings with user access cleared

[Linus Torvalds]

On Wed, Dec 13, 2017 at 10:21 AM, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> On 12/13/2017 10:08 AM, Linus Torvalds wrote:
>> On Wed, Dec 13, 2017 at 7:54 AM, Peter Zijlstr <peterz@xxxxxxxxxxxxx> wrote:
>>> Which is why get_user_pages() _should_ enforce this.
>>>
>>> What use are protection keys if you can trivially circumvent them?
>> No, we will *not* worry about protection keys in get_user_pages().
>
> We did introduce some support for it here:
>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=33a709b25a760b91184bb335cf7d7c32b8123013

Ugh. I never realized.

We should revert that, I feel. It's literally extra complexity for no
actual real gain, and there is a real downside: the extra complexity
that will cause people to get things wrong.

This thread about us getting it wrong is just the proof. I vote for
not trying to "fix" this case, let's just remove it.

                  Linus