Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary

H. Peter Anvin
2011-07-01T16:00:44Z

On 07/01/2011 08:36 AM, Ingo Molnar wrote:
>
> So we could kill multiple birds with the same stone here:
>
> - remove various ugly uses of /dev/mem (including the rootkit usage),
> with or without strict-devmem
>
> - extending it to above-4G for inspection purposes
>
> - allowing to kill /dev/mem access runtime similar to the
> disable_modules lock-down killswitch, for the so inclined.
>
> Would you be interested in modifying your patch-set in such a
> fashion?
>

There is another use that I have looked at, as well: for testing
purposes, it would be extremely good to be able to dirty and/or flush an
arbitrary physical cache line for testing purposes.

This is very very similar to /dev/mem usage -- access to an arbitrary
chunk of memory -- and a fully enabled /dev/mem can of course support
this use (just mmap the page with the relevant cache line). However, it
could also be a separate device which could have looser permissions than
/dev/mem; or a set of ioctls on /dev/mem with a separate kill switch,
because no data would ever be have modified or returned to user space.

Either way, though, we found that it would share a lot of code with the
/dev/mem implementation, and as such fixing up the underlying machinery
is the sanest way to upstream this.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.