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

["Xing, Cedric" <cedric.xing@intel.com>]

> -----Original Message-----
> From: Christopherson, Sean J
> Sent: Monday, June 03, 2019 1:37 PM
> To: Hansen, Dave <dave.hansen@intel.com>
> Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>; Andy Lutomirski
> <luto@kernel.org>; Xing, Cedric <cedric.xing@intel.com>; Stephen Smalley
> <sds@tycho.nsa.gov>; James Morris <jmorris@namei.org>; Serge E . Hallyn
> <serge@hallyn.com>; LSM List <linux-security-module@vger.kernel.org>;
> Paul Moore <paul@paul-moore.com>; Eric Paris <eparis@parisplace.org>;
> selinux@vger.kernel.org; Jethro Beekman <jethro@fortanix.com>; Thomas
> Gleixner <tglx@linutronix.de>; Linus Torvalds <torvalds@linux-
> foundation.org>; LKML <linux-kernel@vger.kernel.org>; X86 ML
> <x86@kernel.org>; linux-sgx@vger.kernel.org; Andrew Morton <akpm@linux-
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> Borislav Petkov <bp@alien8.de>; Josh Triplett <josh@joshtriplett.org>;
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> Roberts, William C <william.c.roberts@intel.com>; Tricca, Philip B
> <philip.b.tricca@intel.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;

What is "flags" here?

> 		__u32	reserved;
> 	}