linux-kernel - Re: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages in single ioctl()

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Date:   Mon, 3 Jun 2019 13:37:12 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Cedric Xing <cedric.xing@...el.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        Jethro Beekman <jethro@...tanix.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, nhorman@...hat.com,
        npmccallum@...hat.com, Serge Ayoun <serge.ayoun@...el.com>,
        Shay Katz-zamir <shay.katz-zamir@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kai Svahn <kai.svahn@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        Kai Huang <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        William Roberts <william.c.roberts@...el.com>,
        Philip Tricca <philip.b.tricca@...el.com>
Subject: Re: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages
 in single ioctl()

On Mon, Jun 03, 2019 at 01:14:45PM -0700, Dave Hansen wrote:
> On 5/31/19 4:31 PM, Sean Christopherson wrote:
> > -struct sgx_enclave_add_page {
> > +struct sgx_enclave_add_pages {
> >  	__u64	addr;
> >  	__u64	src;
> >  	__u64	secinfo;
> > +	__u32	nr_pages;
> >  	__u16	mrmask;
> >  } __attribute__((__packed__));
> 
> IMNHO this follows a user interface anti-pattern: exposing page sizes
> where not strictly required.
> 
> Think of how this would look to an application if page size was
> variable.  With this interface, they always need to scale their
> operations by page size instead of just aligning it.

I briefly considered taking size in bytes, but I took a shortcut because
EPC pages are architecturally defined to be 4k sized and aligned.  That
being said, I don't necessarily disagree, especially if nr_pages isn't
squeezed into a u32.
 
> BTW, why is nr_pages a u32?  Do we never envision a case where you can
> add more than 4TB of memory to an enclave? ;)

Heh, fair enough.  IIRC, a while back someone posted about having problems
building a 512gb enclave in a 92mb EPC...

How about this for the intermediate patch:

	struct sgx_enclave_add_region {
		__u64	addr;
		__u64	src;
		__u64	size;
		__u64	secinfo;
		__u16	mrmask;
		__u16	reserved16;
		__u32	reserved;
	}

and with the flags field:

	struct sgx_enclave_add_region {
		__u64	addr;
		__u64	src;
		__u64	size;
		__u64	secinfo;
		__u16	mrmask;
		__u16	flags;
		__u32	reserved;
	}