> On Feb 22, 2019, at 10:28 AM, Linus Torvalds <torva...@linux-foundation.org>
> wrote:
>
>> On Fri, Feb 22, 2019 at 9:48 AM Andy Lutomirski <l...@amacapital.net> wrote:
>>
>>> On Feb 22, 2019, at 9:43 AM, Linus Torvalds <torva...@linux-foundation.org>
>>> wrote:
>>>
>>> Then we should still probably fix up "__probe_kernel_read()" to not
>>> allow user accesses. The easiest way to do that is actually likely to
>>> use the "unsafe_get_user()" functions *without* doing a
>>> uaccess_begin(), which will mean that modern CPU's will simply fault
>>> on a kernel access to user space.
>>>
>>> The nice thing about that is that usually developers will have access
>>> to exactly those modern boxes, so the people who notice that it
>>> doesn't work are the right people.
>>
>> We use probe_kernel_read() from oops code. I’d rather it return -EFAULT than
>> oops harder and kill the first oops.
>
> It would still do that.
>
> Using the unsafe_get_user() macros doesn't remove the exception
> handling, and we wouldn't remove the whole "pagefault_disable()"
> either. So it would work exactly the same way it does now, except on a
> modern CPU it would return -EFAULT for a user space access due to AC
> not being set.
>
>
Hmm. I misunderstood you. I thought you wanted the oops.
We’d have to check that we don’t trip the “SMAP violation, egads!” check.
