Re: [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor

["Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>]

On 9/23/20 3:51 PM, Pavel Machek wrote:
> Hi!
> 
>>>> Scenario 2
>>>> ----------
>>>>
>>>> We know what code we need in advance. User trampolines are a good example of
>>>> this. It is possible to define such code statically with some help from the
>>>> kernel.
>>>>
>>>> This RFC addresses (2). (1) needs a general purpose trusted code generator
>>>> and is out of scope for this RFC.
>>>
>>> This is slightly less crazy talk than introduction talking about holes
>>> in W^X. But it is very, very far from normal Unix system, where you
>>> have selection of interpretters to run your malware on (sh, python,
>>> awk, emacs, ...) and often you can even compile malware from sources. 
>>>
>>> And as you noted, we don't have "a general purpose trusted code
>>> generator" for our systems.
>>>
>>> I believe you should simply delete confusing "introduction" and
>>> provide details of super-secure system where your patches would be
>>> useful, instead.
>>
>> This RFC talks about converting dynamic code (which cannot be authenticated)
>> to static code that can be authenticated using signature verification. That
>> is the scope of this RFC.
>>
>> If I have not been clear before, by dynamic code, I mean machine code that is
>> dynamic in nature. Scripts are beyond the scope of this RFC.
>>
>> Also, malware compiled from sources is not dynamic code. That is orthogonal
>> to this RFC. If such malware has a valid signature that the kernel permits its
>> execution, we have a systemic problem.
>>
>> I am not saying that script authentication or compiled malware are not problems.
>> I am just saying that this RFC is not trying to solve all of the security problems.
>> It is trying to define one way to convert dynamic code to static code to address
>> one class of problems.
> 
> Well, you don't have to solve all problems at once.
> 
> But solutions have to exist, and AFAIK in this case they don't. You
> are armoring doors, but ignoring open windows.
> 

I am afraid I don't agree that the other open security issues must be
addressed for this RFC to make sense. If you think that any of those
issues actually has a bad interaction/intersection with this RFC,
let me know how and I will address it.

> Or very probably you are thinking about something different than
> normal desktop distros (Debian 10). Because on my systems, I have
> python, gdb and gcc...
> 
> It would be nice to specify what other pieces need to be present for
> this to make sense -- because it makes no sense on Debian 10.
> 

Since this RFC pertains to converting dynamic machine code to static
code, it has nothing to do with the other items you have mentioned.
I am not disagreeing that the other items need to be addressed. But
they are orthogonal.

Madhavan