Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

[Jarkko Sakkinen]

On Tue, Dec 18, 2018 at 03:17:25AM +0200, Jarkko Sakkinen wrote:
> On Mon, Dec 17, 2018 at 11:12:21AM -0800, Andy Lutomirski wrote:
> > I'm going to ask an obnoxious high-level question: why does an enclave
> > even refer to a specific mm?
> 
> The reason is that it has not been yet in focus in the review process
> and there has been other concerns.
> 
> At least the code is fairly stable i.e. working code is usually good
> starting point for making something different (ignoring the recent
> regression caused by the shmem to VMA migration).
> 
> > If I were designing this thing, and if I hadn't started trying to
> > implement it, my first thought would be that an enclave tracks its
> > linear address range, which is just a pair of numbers, and also keeps
> > track of a whole bunch of physical EPC pages, data structures, etc.
> > And that mmap() gets rejected unless the requested virtual address
> > matches the linear address range that the enclave wants and, aside
> > from that, just creates a VMA that keeps a reference to the enclave.
> > (And, for convenience, I suppose that the first mmap() call done
> > before any actual enclave setup happens could choose any address and
> > then cause the enclave to lock itself to that address, although a
> > regular anonymous PROT_NONE MAP_NORESERVE mapping would do just fine,
> > too.)  And the driver would explicitly allow multiple different mms to
> > have the same enclave mapped.  More importantly, a daemon could set up
> > an enclave without necessarily mapping it at all and then SCM_RIGHTS
> > the enclave over to the process that plans to run it.
> 
> The current SGX_IOC_ENCLAVE_CREATE ioctl would be trivial to change to
> use this approach. Instead looking up VMA with an enclave instance it
> would create a new enclave instance.
> 
> Then we could have SGX_IOC_ENCLAVE_ATTACH to attach an enclave to a VMA.
> 
> This does not sound too complicated.
> 
> > Now I'm sure this has all kinds of problems, such as the ISA possibly
> > making it rather obnoxious to add pages to the enclave without having
> > it mapped.  But these operations could, in principle, be done by
> 
> We do EADD in a kthread. What this would require to put current->mm
> into a request that it is processed by that thread. This would be
> doable with mmget().

Correction here. We need mm just for vm_insert_pfn(), which would be
removed, no need to pass mm.

/Jarkko