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

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Message-ID: <CALCETrUb4X9_L9RXKhmyNpfSCsbNodP=BfbfO8Fz_efq24jp8w@mail.gmail.com>
Date:   Tue, 4 Jun 2019 13:18:13 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     "Xing, Cedric" <cedric.xing@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        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()

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.