From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: "intel-sgx-kernel-dev@lists.01.org"
<intel-sgx-kernel-dev@lists.01.org>,
"platform-driver-x86@vger.kernel.org"
<platform-driver-x86@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Darren Hart <dvhart@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andy Shevchenko <andy@infradead.org>
Subject: Re: [intel-sgx-kernel-dev] [PATCH v7 4/8] intel_sgx: driver for Intel Software Guard Extensions
Date: Tue, 12 Dec 2017 13:46:48 -0800 [thread overview]
Message-ID: <1513115208.27842.18.camel@intel.com> (raw)
In-Reply-To: <37306EFA9975BE469F115FDE982C075BC6B39E1D@ORSMSX108.amr.corp.intel.com>
On Fri, 2017-12-08 at 07:31 -0800, Christopherson, Sean J wrote:
> Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> > On Thu, Dec 07, 2017 at 02:46:39PM +0000, Christopherson, Sean J wrote:
> > > > + for (i = 0; i < 2; i++) {
> > > > + va_page = list_first_entry(&encl->va_pages,
> > > > + struct sgx_va_page, list);
> > > > + va_offset = sgx_alloc_va_slot(va_page);
> > > > + if (va_offset < PAGE_SIZE)
> > > > + break;
> > > > +
> > > > + list_move_tail(&va_page->list, &encl->va_pages);
> > > > + }
> > >
> > > This is broken, there is no guarantee that the next VA page will have
> > > a free slot. You have to walk over all VA pages to guarantee a slot
> > > is found, e.g. this caused EWB and ELDU errors.
> >
> > I did run some extensive stress tests on this and did not experience any
> > issues. Full VA pages are always put to the end. Please point me to the
> > test where this breaks so that I can fix the issue if it persists.
>
> Three VA pages in the enclave: A, B and C. Evict all pages in the
> enclave, i.e. consume all slots in A, B and C. The list can be in
> any order at this point, but for the sake of argument let's say the
> order is C->A->B, i.e. C was originally the last VA page in the list.
> Fault in page X, whose VA is in B. Evict X. This code looks at C
> and A, and finds no available slot, but continues with VA page A and
> a va_offset of PAGE_SIZE.
So it looks like you avoid the described case by moving B to the head of
the list in sgx_eldu. The bug I am seeing is still straightforward to
theorize:
1. Three VA pages. List = A->B->C
2. Fill A and B, use one entry in C. List = C->B->A
3. ELDU, freeing a slot in B. List = B->C->A
4. EWB, consuming the last slot in B. List = B->C->A
5. ELDU, freeing a slot in A. List = A->B->C
6. EWB, consuming the last slot in A. List = A->B->C
7. ELDU, but both A and B are full
8. Explode
next prev parent reply other threads:[~2017-12-12 21:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-07 1:54 [PATCH v7 0/8] Intel SGX Driver Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 1/8] intel_sgx: updated MAINTAINERS Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 2/8] x86: add SGX definitions to cpufeature Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 3/8] x86: add SGX definitions to msr-index.h Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 4/8] intel_sgx: driver for Intel Software Guard Extensions Jarkko Sakkinen
2017-12-07 14:46 ` [intel-sgx-kernel-dev] " Christopherson, Sean J
2017-12-07 16:05 ` Jarkko Sakkinen
2017-12-07 16:12 ` Jarkko Sakkinen
2017-12-08 15:31 ` Christopherson, Sean J
2017-12-14 12:42 ` Jarkko Sakkinen
2017-12-12 21:32 ` Sean Christopherson
2017-12-14 13:03 ` Jarkko Sakkinen
[not found] ` <37306EFA9975BE469F115FDE982C075BC6B39E1D@ORSMSX108.amr.corp.intel.com>
2017-12-12 21:46 ` Sean Christopherson [this message]
2017-12-14 13:10 ` Jarkko Sakkinen
2017-12-14 21:36 ` Christopherson, Sean J
2017-12-15 15:02 ` Jarkko Sakkinen
2017-12-12 7:42 ` Ayoun, Serge
2017-12-07 1:54 ` [PATCH v7 5/8] intel_sgx: ptrace() support Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 6/8] intel_sgx: driver documentation Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 7/8] fs/pipe.c: export create_pipe_files() Jarkko Sakkinen
2017-12-07 1:54 ` [PATCH v7 8/8] intel_sgx: in-kernel launch enclave Jarkko Sakkinen
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