Re: [RFC] MemoryProtectionLib for Dynamic Memory Guard Settings


Taylor Beebe
 

I am going to extend the opportunity for feedback to the end of Tuesday. I would very much like more community input on this proposal.

On 7/30/2021 11:42 AM, Sean Brogan wrote:
Jiewen,
**Slight rant**
I agree with libraries as an effective abstraction method.  But I think there needs to be a broad discussion about the order of preference for methods of abstraction.  Today the edk2 code base is a mix and often there are numerous methods abstracting the same thing which leads to confusion, misconfiguration, and error.
In the UEFI specification we have PPIs/Protocols/Events for functional abstraction.  We have variables, guided config tables, and HII for data abstraction.
In the PI specification we add HOBs and PCDs for data abstractions.
Finally, in EDKII we add the library class concept and leverage it heavily for arch, phase, and platform/behavioral abstractions.
Without clear guidance for how and when to use the above it is hard to keep code being developed by the larger community consistent.
**End**
I was leaning towards something closer to

>> Option 1:
https://github.com/TaylorBeebe/edk2/tree/memory_protection_lib_2
the HOB method and internally as we develop more code we are preferring HOB and data abstractions more than functional abstraction.  Data abstractions can be used to control functional differences as well if needed.  Data abstractions allow for easier validation and support diverse code environments.  For example standalone MM and payloadpkg/payload concepts.  Finally, data abstractions break the need for a monolithic code base.   But as you can see in option 1 it actually uses a library class abstraction as well because no one wants to write the same code over and over again to get the HOB.  The contract of the library is just data but it still requires library mappings.  Maybe these types of libraries need to be treated differently.
Anyway it would be great to hear from other members of the community around not just the memory protections RFC (this RFC) but around preferences for abstraction techniques (pro/con).  If an actual discussion starts it could move to design meeting.
Thanks
Sean
On 7/29/2021 7:34 PM, Yao, Jiewen wrote:
Thanks. Code talks better.

I prefer option 2, which is a generic way for abstraction.

And you may enable option 1 under the cover of option 2, just create a lib instance to get config from Hob.

Thank you
Yao Jiewen

-----Original Message-----
From: Taylor Beebe <t@taylorbeebe.com>
Sent: Friday, July 30, 2021 10:07 AM
To: Yao, Jiewen <jiewen.yao@intel.com>; Wang, Jian J <jian.j.wang@intel.com>;
devel@edk2.groups.io
Cc: spbrogan@outlook.com; Dong, Eric <eric.dong@intel.com>; Ni, Ray
<ray.ni@intel.com>; Kumar, Rahul1 <rahul1.kumar@intel.com>;
mikuback@linux.microsoft.com; Wu, Hao A <hao.a.wu@intel.com>; Bi, Dandan
<dandan.bi@intel.com>; gaoliming@byosoft.com.cn; Dong, Guo
<guo.dong@intel.com>; Ma, Maurice <maurice.ma@intel.com>; You, Benjamin
<benjamin.you@intel.com>
Subject: Re: [RFC] MemoryProtectionLib for Dynamic Memory Guard Settings

Of course - here are a couple of rough drafts:

Option 1: https://github.com/TaylorBeebe/edk2/tree/memory_protection_lib_2
Option 2: https://github.com/TaylorBeebe/edk2/tree/memory_protection_lib

On 7/29/2021 6:57 PM, Yao, Jiewen wrote:
Hi
Sorry, I am not able to follow the discussion.

Is there any sample or POC code to show the concept?

-----Original Message-----
From: Taylor Beebe <t@taylorbeebe.com>
Sent: Friday, July 30, 2021 9:55 AM
To: Wang, Jian J <jian.j.wang@intel.com>; devel@edk2.groups.io
Cc: spbrogan@outlook.com; Dong, Eric <eric.dong@intel.com>; Ni, Ray
<ray.ni@intel.com>; Kumar, Rahul1 <rahul1.kumar@intel.com>;
mikuback@linux.microsoft.com; Wu, Hao A <hao.a.wu@intel.com>; Bi,
Dandan
<dandan.bi@intel.com>; gaoliming@byosoft.com.cn; Dong, Guo
<guo.dong@intel.com>; Ma, Maurice <maurice.ma@intel.com>; You,
Benjamin
<benjamin.you@intel.com>; Yao, Jiewen <jiewen.yao@intel.com>
Subject: Re: [RFC] MemoryProtectionLib for Dynamic Memory Guard Settings

Thanks for your feedback, Jian.

In option 2, a most basic implementation would returning the current
FixedAtBuild PCDs assuming they are kept. If they aren't, the library
implementer could simply hard-code the return value for each memory
protection setting.

In option 1, the HOB would be published in pre-mem and I'm not an expert
on exploiting the pre-mem environment. Jiewen may have more to say on
this.

-Taylor

On 7/28/2021 7:18 PM, Wang, Jian J wrote:
Thanks for the RFC. I'm not object to this idea. The only concern from me
is the potential security holes introduced by the changes. According to your
description, it allows 3rd party software to violate memory protection
policy.
I'd like to see more explanations on how to avoid it to be exploited.

+Jiewen, what's current process to evaluate the security threat?

Regards,
Jian

-----Original Message-----
From: Taylor Beebe <t@taylorbeebe.com>
Sent: Friday, July 23, 2021 8:33 AM
To: devel@edk2.groups.io
Cc: spbrogan@outlook.com; Dong, Eric <eric.dong@intel.com>; Ni, Ray
<ray.ni@intel.com>; Kumar, Rahul1 <Rahul1.Kumar@intel.com>;
mikuback@linux.microsoft.com; Wang, Jian J <jian.j.wang@intel.com>;
Wu,
Hao A <hao.a.wu@intel.com>; Bi, Dandan <dandan.bi@intel.com>;
gaoliming@byosoft.com.cn; Dong, Guo <guo.dong@intel.com>; Ma,
Maurice
<maurice.ma@intel.com>; You, Benjamin <benjamin.you@intel.com>
Subject: [RFC] MemoryProtectionLib for Dynamic Memory Guard Settings

Current memory protection settings rely on FixedAtBuild PCD values
(minus PcdSetNxForStack). Because of this, the memory protection
configuration interface is fixed in nature. Cases arise in which memory
protections might need to be adjusted between boots (if platform design
allows) to avoid disabling a system. For example, platforms might choose
to allow the user to control their protection policies such as allow
execution of critical 3rd party software that might violate memory
protections.

This RFC seeks your feedback regarding introducing an interface that
allows dynamic configuration of memory protection settings.

I would like to propose two options:
1. Describing the memory protection setting configuration in a HOB that
is produced by the platform.
2. Introducing a library class (e.g. MemoryProtectionLib) that allows
abstraction of the memory protection setting configuration data source.

In addition, I would like to know if the memory protection FixedAtBuild
PCDs currently in MdeModulePkg can be removed so we can move the
configuration interface entirely to an option above.

In any case, I would like the settings to be visible to environments
such as Standalone MM where dynamic PCDs are not accessible.

I am seeking your feedback on this proposal in preparation for sending
an edk2 patch series.

--
Taylor Beebe
Software Engineer @ Microsoft
--
Taylor Beebe
Software Engineer @ Microsoft
--
Taylor Beebe
Software Engineer @ Microsoft


--
Taylor Beebe
Software Engineer @ Microsoft

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