On 23/09/2020 22:51, Pavel Machek wrote:

Hi!

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Scenario 2
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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.

FYI, script execution is being addressed (for the kernel part) by this
patch series:
https://lore.kernel.org/lkml/20200924153228.387737-1-mic@digikod.net/ (local)

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 doesn't make sense for a tailored security system to leave all these
tools available to an attacker.

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.

Not all kernel features make sense for a generic/undefined usage,
especially specific security mechanisms (e.g. SELinux, Smack, Tomoyo,
SafeSetID, LoadPin, IMA, IPE, secure/trusted boot, lockdown, etc.), but
they can still be definitely useful.

Best regards,
									Pavel