From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
x86@kernel.org, linux-sgx@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org,
Jethro Beekman <jethro@fortanix.com>,
Haitao Huang <haitao.huang@linux.intel.com>,
Chunyang Hui <sanqian.hcy@antfin.com>,
Jordan Hand <jorhand@linux.microsoft.com>,
Nathaniel McCallum <npmccallum@redhat.com>,
Seth Moore <sethmo@google.com>,
Suresh Siddha <suresh.b.siddha@intel.com>,
akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
asapek@google.com, cedric.xing@intel.com,
chenalexchen@google.com, conradparker@google.com,
cyhanish@google.com, dave.hansen@intel.com,
haitao.huang@intel.com, josh@joshtriplett.org,
kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com,
ludloff@google.com, luto@kernel.org, nhorman@redhat.com,
puiterwijk@redhat.com, rientjes@google.com, tglx@linutronix.de,
yaozhangx@google.com
Subject: Re: [PATCH v33 11/21] x86/sgx: Linux Enclave Driver
Date: Mon, 29 Jun 2020 08:27:19 -0700 [thread overview]
Message-ID: <20200629152718.GA12312@linux.intel.com> (raw)
In-Reply-To: <20200627174335.GC15585@zn.tnic>
On Sat, Jun 27, 2020 at 07:43:35PM +0200, Borislav Petkov wrote:
> On Thu, Jun 18, 2020 at 01:08:33AM +0300, Jarkko Sakkinen wrote:
> > +static int sgx_encl_init(struct sgx_encl *encl, struct sgx_sigstruct *sigstruct,
> > + void *token)
> > +{
> > + u64 mrsigner[4];
> > + int ret;
> > + int i;
> > + int j;
> > +
> > + /* Check that the required attributes have been authorized. */
> > + if (encl->secs_attributes & ~encl->allowed_attributes)
> > + return -EACCES;
> > +
> > + ret = sgx_get_key_hash(sigstruct->modulus, mrsigner);
> > + if (ret)
> > + return ret;
> > +
> > + mutex_lock(&encl->lock);
> > +
> > + if (atomic_read(&encl->flags) & SGX_ENCL_INITIALIZED) {
> > + ret = -EFAULT;
> > + goto err_out;
> > + }
>
> That test should be the first thing this function or its caller does.
Hmm, I was going to say that SGX_ENCL_INITIALIZED can't be checked until
encl->lock is held, but that's not true for this path as mutual exclusion
is provided by the SGX_ENCL_IOCTL flag. So yeah, this can be checked at
the same time as SGX_ENCL_CREATED in sgx_ioc_enclave_init().
> > + for (i = 0; i < SGX_EINIT_SLEEP_COUNT; i++) {
> > + for (j = 0; j < SGX_EINIT_SPIN_COUNT; j++) {
>
> Ew, what's that double-loop for?
>
> It tries to init an enclave a bunch of times. Why does it need to init
> more than once?
ENCLS[EINIT] is interruptible because it has such a high latency, e.g. 50k+
cycles on success. If an IRQ/NMI/SMI becomes pending, EINIT may fail with
SGX_UNMASKED_EVENT so that the event can be serviced.
The idea behind the double loop is to try EINIT in a tight loop, then back
off and sleep for a while before retrying that tight inner loop.
> > + ret = sgx_einit(sigstruct, token, encl->secs.epc_page,
> > + mrsigner);
> > + if (ret == SGX_UNMASKED_EVENT)
> > + continue;
> > + else
> > + break;
> > + }
> > +
> > + if (ret != SGX_UNMASKED_EVENT)
> > + break;
> > +
> > + msleep_interruptible(SGX_EINIT_SLEEP_TIME);
> > +
> > + if (signal_pending(current)) {
> > + ret = -ERESTARTSYS;
> > + goto err_out;
> > + }
> > + }
> > +
> > + if (ret & ENCLS_FAULT_FLAG) {
> > + if (encls_failed(ret))
> > + ENCLS_WARN(ret, "EINIT");
> > +
> > + sgx_encl_destroy(encl);
> > + ret = -EFAULT;
> > + } else if (ret) {
> > + pr_debug("EINIT returned %d\n", ret);
> > + ret = -EPERM;
> > + } else {
> > + atomic_or(SGX_ENCL_INITIALIZED, &encl->flags);
> > + }
> > +
> > +err_out:
> > + mutex_unlock(&encl->lock);
> > + return ret;
> > +}
> > +
> > +/**
> > + * sgx_ioc_enclave_init - handler for %SGX_IOC_ENCLAVE_INIT
> > + *
> > + * @filep: open file to /dev/sgx
>
> @encl: pointer to an enclave instance (via ioctl() file pointer)
>
> > + * @arg: userspace pointer to a struct sgx_enclave_init instance
> > + *
> > + * Flush any outstanding enqueued EADD operations and perform EINIT. The
> > + * Launch Enclave Public Key Hash MSRs are rewritten as necessary to match
> > + * the enclave's MRSIGNER, which is caculated from the provided sigstruct.
> > + *
> > + * Return:
> > + * 0 on success,
> > + * SGX error code on EINIT failure,
> > + * -errno otherwise
> > + */
> > +static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
> > +{
> > + struct sgx_sigstruct *sigstruct;
> > + struct sgx_enclave_init einit;
> > + struct page *initp_page;
> > + void *token;
> > + int ret;
> > +
> > + if (!(atomic_read(&encl->flags) & SGX_ENCL_CREATED))
>
> Might just as well check the other flags: doing EINIT on an already
> initialized enclave - SGX_ENCL_INITIALIZED - is perhaps a nono or
> similarly on a SGX_ENCL_DEAD enclave.
>
> And you could do similar sanity checks in the other ioctl functions.
Ya, as above, SGX_ENCL_INITIALIZED can be checked here.
SGX_ENCL_DEAD is actually already checked in in the top level sgx_ioctl(),
i.e. the check in sgx_encl_add_page() can technically be flat out dropped.
I say "technically" because I'm a bit torn over SGX_ENCL_DEAD; encl->lock
must be held to SGX_ENCL_DEAD (the page fault and reclaim flows rely on
this), but as it stands today only ioctl() paths (guarded by SGX_ENCL_IOCTL)
and sgx_release() (makes the ioctls() unreachable) set SGX_ENCL_DEAD.
So it's safe to check SGX_ENCL_DEAD from ioctl() context without holding
encl->lock, at least in the current code base, but it feels weird/sketchy.
In the end I don't think I have a strong opinion. Removing the technically
unnecessary DEAD check in sgx_encl_add_page() is the simplest change, so it
may make sense to do that and nothing more for initial upstreaming. Long
term, I fully expect we'll add paths that set SGX_ENCL_DEAD outside of
ioctl() context, e.g. to handle EPC OOM, but it wouldn't be a bad thing to
have a standalone commit in a future series to add DEAD checks (under
encl->lock) in the ADD and INIT flows.
next prev parent reply other threads:[~2020-06-29 18:59 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-17 22:08 [PATCH v33 00/21] Intel SGX foundations Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 01/21] x86/cpufeatures: x86/msr: Add Intel SGX hardware bits Jarkko Sakkinen
2020-06-22 17:37 ` Borislav Petkov
2020-06-25 1:25 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 02/21] x86/cpufeatures: x86/msr: Add Intel SGX Launch Control " Jarkko Sakkinen
2020-06-24 13:04 ` Borislav Petkov
2020-06-24 14:34 ` Sean Christopherson
2020-06-25 1:28 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 03/21] x86/mm: x86/sgx: Signal SIGSEGV with PF_SGX Jarkko Sakkinen
2020-06-25 8:59 ` Borislav Petkov
2020-06-25 15:34 ` Sean Christopherson
2020-06-25 16:49 ` Borislav Petkov
2020-06-25 20:52 ` Jarkko Sakkinen
2020-06-25 21:11 ` Borislav Petkov
2020-06-26 13:34 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 04/21] x86/sgx: Add SGX microarchitectural data structures Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 05/21] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 06/21] x86/cpu/intel: Detect SGX support Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 07/21] x86/cpu/intel: Add nosgx kernel parameter Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 08/21] x86/sgx: Initialize metadata for Enclave Page Cache (EPC) sections Jarkko Sakkinen
2020-06-25 10:14 ` Borislav Petkov
2020-06-25 20:11 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 09/21] x86/sgx: Add __sgx_alloc_epc_page() and sgx_free_epc_page() Jarkko Sakkinen
2020-06-25 17:06 ` Borislav Petkov
2020-06-25 20:55 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 10/21] mm: Introduce vm_ops->may_mprotect() Jarkko Sakkinen
2020-06-25 17:14 ` Borislav Petkov
2020-06-25 17:30 ` Matthew Wilcox
2020-06-25 18:06 ` Sean Christopherson
2020-06-25 22:40 ` Jarkko Sakkinen
2020-06-25 22:26 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 11/21] x86/sgx: Linux Enclave Driver Jarkko Sakkinen
2020-06-25 17:23 ` Borislav Petkov
2020-06-25 18:34 ` Sean Christopherson
2020-06-25 18:45 ` Borislav Petkov
2020-06-26 14:19 ` Jarkko Sakkinen
2020-06-25 20:21 ` Jarkko Sakkinen
2020-06-25 20:25 ` Borislav Petkov
2020-06-26 13:40 ` Jarkko Sakkinen
2020-06-25 18:53 ` Borislav Petkov
2020-06-26 14:17 ` Jarkko Sakkinen
2020-06-26 9:14 ` Borislav Petkov
2020-06-26 14:16 ` Sean Christopherson
2020-06-26 14:20 ` Borislav Petkov
2020-07-03 23:04 ` Jarkko Sakkinen
2020-07-03 3:09 ` Jarkko Sakkinen
2020-06-26 15:34 ` Borislav Petkov
2020-07-04 0:13 ` Jarkko Sakkinen
2020-10-26 21:26 ` Dave Hansen
2020-10-27 1:52 ` Jarkko Sakkinen
2020-10-27 10:05 ` Borislav Petkov
2020-10-27 15:20 ` Dave Hansen
2020-10-27 15:37 ` Borislav Petkov
2020-06-27 17:43 ` Borislav Petkov
2020-06-29 15:27 ` Sean Christopherson [this message]
2020-06-29 15:37 ` Borislav Petkov
2020-07-04 1:43 ` Jarkko Sakkinen
2020-07-07 1:38 ` Sean Christopherson
2020-07-07 3:29 ` Jarkko Sakkinen
2020-07-04 1:42 ` Jarkko Sakkinen
2020-07-02 3:59 ` Sean Christopherson
2020-07-04 3:31 ` Jarkko Sakkinen
2020-09-02 3:06 ` Haitao Huang
2020-09-02 16:10 ` Sean Christopherson
2020-09-02 18:40 ` Haitao Huang
2020-09-04 12:01 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 12/21] x86/sgx: Allow a limited use of ATTRIBUTE.PROVISIONKEY for attestation Jarkko Sakkinen
2020-06-29 16:02 ` Borislav Petkov
2020-06-29 22:04 ` Sean Christopherson
2020-06-30 8:49 ` Borislav Petkov
2020-06-30 14:20 ` Sean Christopherson
2020-06-30 17:13 ` Andy Lutomirski
2020-07-02 20:47 ` Dr. Greg
2020-07-03 2:43 ` Jarkko Sakkinen
2020-07-03 2:38 ` Jarkko Sakkinen
2020-07-03 2:32 ` Jarkko Sakkinen
2020-07-03 2:55 ` Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 13/21] x86/sgx: Add a page reclaimer Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 14/21] x86/sgx: ptrace() support for the SGX driver Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 15/21] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen
2020-06-29 17:10 ` Borislav Petkov
2020-06-30 6:00 ` Sean Christopherson
2020-06-30 8:41 ` Borislav Petkov
2020-06-30 14:55 ` Sean Christopherson
2020-06-30 16:48 ` Andy Lutomirski
2020-06-30 17:23 ` Sean Christopherson
2020-07-02 12:52 ` Thomas Gleixner
2020-06-17 22:08 ` [PATCH v33 16/21] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 17/21] x86/traps: Attempt to fixup exceptions in vDSO before signaling Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 18/21] x86/vdso: Implement a vDSO for Intel SGX enclave call Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 19/21] selftests/x86: Add a selftest for SGX Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 20/21] docs: x86/sgx: Document SGX micro architecture and kernel internals Jarkko Sakkinen
2020-06-17 22:08 ` [PATCH v33 21/21] x86/sgx: Update MAINTAINERS Jarkko Sakkinen
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