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Date:   Mon, 6 Jul 2020 18:38:47 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     Borislav Petkov <bp@alien8.de>, 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,
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        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
Message-ID: <20200707013847.GA5208@linux.intel.com>
References: <20200617220844.57423-1-jarkko.sakkinen@linux.intel.com>
 <20200617220844.57423-12-jarkko.sakkinen@linux.intel.com>
 <20200627174335.GC15585@zn.tnic>
 <20200629152718.GA12312@linux.intel.com>
 <20200704014349.GB129411@linux.intel.com>
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On Sat, Jul 04, 2020 at 04:43:49AM +0300, Jarkko Sakkinen wrote:
> On Mon, Jun 29, 2020 at 08:27:19AM -0700, Sean Christopherson wrote:
> > On Sat, Jun 27, 2020 at 07:43:35PM +0200, Borislav Petkov wrote:
> > > 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.
> 
> AFAIK nonne of th ioctl's should not need SGX_ENCL_DEAD check.

I can't tell if the double negative was intended, but I took a peek at your
current master and see that you removed the SGX_ENCL_DEAD check in
sgx_ioctl().  That check needs to stay, e.g. if EEXTEND fails we absolutely
need to prevent any further operations on the enclave.

The above was calling out that additional checks on SGX_ENCL_DEAD after
acquiring encl->lock are not necessary because SGX_ENCL_DEAD can only be
set when the ioctls() are no longer reachable or from within an ioctl(),
which provides exclusivity via SGX_ENCL_IOCTL.