[edk2-devel] [RFC] MemoryProtectionLib for Dynamic Memory Guard Settings

Fri Jul 30 18:42:23 UTC 2021

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 at taylorbeebe.com>
>> Sent: Friday, July 30, 2021 10:07 AM
>> To: Yao, Jiewen <jiewen.yao at intel.com>; Wang, Jian J <jian.j.wang at intel.com>;
>> devel at edk2.groups.io
>> Cc: spbrogan at outlook.com; Dong, Eric <eric.dong at intel.com>; Ni, Ray
>> <ray.ni at intel.com>; Kumar, Rahul1 <rahul1.kumar at intel.com>;
>> mikuback at linux.microsoft.com; Wu, Hao A <hao.a.wu at intel.com>; Bi, Dandan
>> <dandan.bi at intel.com>; gaoliming at byosoft.com.cn; Dong, Guo
>> <guo.dong at intel.com>; Ma, Maurice <maurice.ma at intel.com>; You, Benjamin
>> <benjamin.you at 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 at taylorbeebe.com>
>>>> Sent: Friday, July 30, 2021 9:55 AM
>>>> To: Wang, Jian J <jian.j.wang at intel.com>; devel at edk2.groups.io
>>>> Cc: spbrogan at outlook.com; Dong, Eric <eric.dong at intel.com>; Ni, Ray
>>>> <ray.ni at intel.com>; Kumar, Rahul1 <rahul1.kumar at intel.com>;
>>>> mikuback at linux.microsoft.com; Wu, Hao A <hao.a.wu at intel.com>; Bi,
>> Dandan
>>>> <dandan.bi at intel.com>; gaoliming at byosoft.com.cn; Dong, Guo
>>>> <guo.dong at intel.com>; Ma, Maurice <maurice.ma at intel.com>; You,
>> Benjamin
>>>> <benjamin.you at intel.com>; Yao, Jiewen <jiewen.yao at 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 at taylorbeebe.com>
>>>>>> Sent: Friday, July 23, 2021 8:33 AM
>>>>>> To: devel at edk2.groups.io
>>>>>> Cc: spbrogan at outlook.com; Dong, Eric <eric.dong at intel.com>; Ni, Ray
>>>>>> <ray.ni at intel.com>; Kumar, Rahul1 <Rahul1.Kumar at intel.com>;
>>>>>> mikuback at linux.microsoft.com; Wang, Jian J <jian.j.wang at intel.com>;
>> Wu,
>>>>>> Hao A <hao.a.wu at intel.com>; Bi, Dandan <dandan.bi at intel.com>;
>>>>>> gaoliming at byosoft.com.cn; Dong, Guo <guo.dong at intel.com>; Ma,
>>>> Maurice
>>>>>> <maurice.ma at intel.com>; You, Benjamin <benjamin.you at 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
> 
> 
> 
> 
> 

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