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

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Message-ID: <613c6814-4e71-38e5-444a-545f0e286df8@fortanix.com>
Date:   Wed, 19 Dec 2018 09:36:16 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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 2018-12-19 14:41, Jarkko Sakkinen wrote:
> 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).

So your plan is that to call EADD, userspace has to pass the device fd 
AND the enclave fd AND the enclave address? That seems a little superfluous.

--
Jethro Beekman | Fortanix


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