Re: [PATCH v9 3/3] x86/sgx: Fine grained SGX MCA behavior for virtualization

[Dave Hansen <dave.hansen@intel.com>]

On 10/13/22 07:40, Zhiquan Li wrote:
>>>> What happens if a hypervisor *DOES* fork()?  What's the fallout?
>>> This part originates from below discussion:
>>>
>>> https://lore.kernel.org/linux-sgx/52dc7f50b68c99cecb9e1c3383d9c6d88734cd67.camel@intel.com/#t
>>>
>>> It intents to answer the question:
>>>
>>>     Do you think the processes sharing the same enclave need to be
>>>     killed, even they had not touched the EPC page with hardware error?
>>>
>>> Dave, do you mean it's not appropriate to be put here?
>> It's actually a pretty important point, but it's still out of the blue.
>>
>> You also didn't answer my question.
> Oh, sorry, I focused on answering "Why is this here?" but forgot to
> answer "What's the fallout?"
> 
> It's a very good question.
> 
> Looks like Kai had answered it before:
> 
> 	For instance, an application can open /dev/sgx_vepc, mmap(), and
> 	fork().  Then if the child does mmap() against the fd opened by
> 	the parent, the child will share the same vepc with the parent.
> 
> 	...
> 
> 	Sharing virtual EPC instance will very likely unexpectedly break
> 	enclaves in all VMs.

How, though?  This basically says, "I think things will break."  I want
to know a few more specifics than that before we merge this.  There are
ABI implications.

> https://lore.kernel.org/linux-sgx/52dc7f50b68c99cecb9e1c3383d9c6d88734cd67.camel@intel.com/#t
> 
> Moreover, I checked the code in below scenario while child sharing the
> virtual EPC instance with parent:
> - child closes /dev/sgx_vepc earlier than parent.
> - child re-mmap() /dev/sgx_vepc to the same memory region as parent.
> - child mmap() /dev/sgx_vepc to different memory region.
> - child accesses the memory region of mmap() inherited from parent.
> 
> It's just that the app messes itself up, the vepc instance is protected
> very well.
> Maybe there are other corner cases I've not considered?

... and what happens when *THIS* patch is in play?  What if there is a
machine check in SGX memory?