linux-kernel - Re: x86/sgx: uapi change proposal

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Date:   Wed, 19 Dec 2018 11:11:48 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jethro Beekman <jethro@...tanix.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Triplett <josh@...htriplett.org>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        "Dr . Greg Wettstein" <greg@...ellic.com>
Subject: Re: x86/sgx: uapi change proposal

On Wed, Dec 19, 2018 at 08:41:12AM +0000, Jethro Beekman wrote:
> One weird thing is the departure from the normal mmap behavior that the
> memory mapping persists even if the original fd is closed. (See man mmap:
> "closing the file descriptor does not unmap the region.")

The mmapped region and enclave would be completely disjoint to start
with. The enclave driver code would assume that an enclave VMA exists
when it maps enclave address space to a process.

I.e. VMA would no longer reference to the enclave or vice versa but
you would still create an enclave VMA with mmap().

This is IMHO very clear and well-defined semantics.

> > struct sgx_enclave_add_page {
> > 	__u64	enclave_fd;
> > 	__u64	src;
> > 	__u64	secinfo;
> > 	__u16	mrmask;
> > } __attribute__((__packed__));
> 
> Wouldn't you just pass enclave_fd as the ioctl fd parameter?

I'm still planning to keep the API in the device fd and use enclave_fd
as handle to the enclave address space. I don't see any obvious reason
to change that behavior.

And if we ever add any "global" ioctls, then we would have to define
APIs to both fd's, which would become a mess.

> How to specify the address of the page that is being added?

Yes, that is correct and my bad to remove it (just quickly drafted what
I had in mind).

/Jarkko