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

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Date:   Tue, 4 Jun 2019 22:02:27 +0000
From:   "Xing, Cedric" <cedric.xing@...el.com>
To:     Andy Lutomirski <luto@...nel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>
CC:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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" <selinux@...r.kernel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        "Hansen, Dave" <dave.hansen@...el.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" <linux-sgx@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        "Tricca, Philip B" <philip.b.tricca@...el.com>
Subject: RE: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages
 in single ioctl()

> From: Andy Lutomirski [mailto:luto@...nel.org]
> Sent: Tuesday, June 04, 2019 1:18 PM
> 
> On Mon, Jun 3, 2019 at 1:39 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > On Mon, Jun 03, 2019 at 01:08:04PM -0700, Sean Christopherson wrote:
> > > On Sun, Jun 02, 2019 at 11:26:09PM -0700, Xing, Cedric wrote:
> > > > > From: Christopherson, Sean J
> > > > > Sent: Friday, May 31, 2019 4:32 PM
> > > > >
> > > > > +/**
> > > > > + * sgx_ioc_enclave_add_pages - handler for
> > > > > +%SGX_IOC_ENCLAVE_ADD_PAGES
> > > > > + *
> > > > > + * @filep:       open file to /dev/sgx
> > > > > + * @cmd: the command value
> > > > > + * @arg: pointer to an &sgx_enclave_add_page instance
> > > > > + *
> > > > > + * Add a range of pages to an uninitialized enclave (EADD), and
> > > > > +optionally
> > > > > + * extend the enclave's measurement with the contents of the
> page (EEXTEND).
> > > > > + * The range of pages must be virtually contiguous.  The
> > > > > +SECINFO and
> > > > > + * measurement maskare applied to all pages, i.e. pages with
> > > > > +different
> > > > > + * properties must be added in separate calls.
> > > > > + *
> > > > > + * EADD and EEXTEND are done asynchronously via worker threads.
> > > > > +A successful
> > > > > + * sgx_ioc_enclave_add_page() only indicates the pages have
> > > > > +been added to the
> > > > > + * work queue, it does not guarantee adding the pages to the
> > > > > +enclave will
> > > > > + * succeed.
> > > > > + *
> > > > > + * Return:
> > > > > + *   0 on success,
> > > > > + *   -errno otherwise
> > > > > + */
> > > > > +static long sgx_ioc_enclave_add_pages(struct file *filep,
> unsigned int cmd,
> > > > > +                               unsigned long arg) {  struct
> > > > > +sgx_enclave_add_pages *addp = (void *)arg;  struct sgx_encl
> > > > > +*encl = filep->private_data;  struct sgx_secinfo secinfo;
> > > > > +unsigned int i;  int ret;
> > > > > +
> > > > > + if (copy_from_user(&secinfo, (void __user *)addp->secinfo,
> > > > > +                    sizeof(secinfo)))
> > > > > +         return -EFAULT;
> > > > > +
> > > > > + for (i = 0, ret = 0; i < addp->nr_pages && !ret; i++) {
> > > > > +         if (signal_pending(current))
> > > > > +                 return -ERESTARTSYS;
> > > >
> > > > If interrupted, how would user mode code know how many pages have
> been EADD'ed?
> > >
> > > Hmm, updating nr_pages would be fairly simple and shouldn't confuse
> > > userspace, e.g. as opposed to overloading the return value.
> >
> > Or maybe update @addr and @src as well?  That would allow userspace to
> > re-invoke the ioctl() without having to modify the struct.
> 
> If you're going to use -ERESTARTSYS, that's the way to go.  -EINTR would
> be an alternative.  A benefit of -ERESTARTSYS is that, with -EINTR, it
> wouldn't be that surprising for user code to simply fail to handle it.

-EINTR means the call was interrupted before anything could be done. Am I correct?

But in this case some pages have been processed already so I guess we cannot return any error code. I think it more reasonable to return the number of pages (or bytes) processed.