Re: [intel-sgx-kernel-dev] [PATCH v4 06/12] fs/pipe.c: export create_pipe_files() and replace_fd()

[Dave Hansen]

On 10/24/2017 06:39 AM, Jarkko Sakkinen wrote:
> On Sun, Oct 22, 2017 at 10:09:16PM -0700, Dave Hansen wrote:
>> On 10/22/2017 07:55 PM, Jarkko Sakkinen wrote:
>>> On Fri, Oct 20, 2017 at 07:32:42AM -0700, Dave Hansen wrote:
>>>> I've always been curious, and the changelog and thread are curiously
>>>> oblique on this topic: what the heck does this driver use pipes *for*?
>>> For communication with the process hosting the launch enclave.
>>
>> But, why pipes?  Why does the kernel have to be the one setting these
>> up?  Why is this communication necessary in the first place?
> 
> 1. Kernel gives a SIGSTRUCT instance to the LE hosting process.
> 2. LE hosting process gives the SIGSTRUCT to the LE.
> 3. LE gives EINITTOKEN to the LE hosting process after generating it.
> 4. LE hosting process gives it back to the kernel.

Let me see if I can turn that into english.  Enclaves are all rooted in
a chain of trust.  To run an enclave, you need to have that enclave
blessed by the hardware or blessed by a "launch enclave" (aka. LE).  The
LE is hosted inside a normal process, just as the enclave we are trying
to launch is hosted in a normal process.  In order to launch a normal
enclave, we talk to the LE which gives us a token that allows us to
start a new enclave.

These pipes are the mechanism that we use so that the process starting
the new process can talk to the launch enclave.

How's that?

> I do not understand why using pipes for this is such a big crime to
> implement this. I do have an alternative proposal if it is.

The crime is not writing a good changelog to explain what you are doing
and why you need to do it.

> What I can do is to use one struct shmem_file instance and assing it
> to a file descriptor instead. Kernel and LE hosting process can then
> use that for communication.

Could you explain a bit about what kind of information needs to go back
and forth?  Is it just "give me a launch key" followed by "here you go",
or is it more complicated than that?