From: Andy Lutomirski <luto@kernel.org>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
"Huang, Kai" <kai.huang@intel.com>,
Jethro Beekman <jethro@fortanix.com>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"x86@kernel.org" <x86@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Haitao Huang <haitao.huang@linux.intel.com>,
"Dr . Greg Wettstein" <greg@enjellic.com>
Subject: Re: x86/sgx: uapi change proposal
Date: Thu, 10 Jan 2019 16:30:06 -0800 [thread overview]
Message-ID: <CALCETrUsj1YBwcEDiyU-seTiCuyFJW+BvunzOUUiUYQj+ojpEg@mail.gmail.com> (raw)
In-Reply-To: <20190110235406.GB2365@linux.intel.com>
On Thu, Jan 10, 2019 at 3:54 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> On Thu, Jan 10, 2019 at 01:34:44PM -0800, Andy Lutomirski wrote:
> > >> On Jan 9, 2019, at 8:31 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> > >>
> > >> On Tue, Jan 08, 2019 at 02:54:11PM -0800, Andy Lutomirski wrote:
> > >
> > >> I do think it makes sense to have QEMU delegate the various ENCLS
> > >> operations (especially EINIT) to the regular SGX interface, which will
> > >> mean that VM guests will have exactly the same access controls applied
> > >> as regular user programs, which is probably what we want.
> > >
> > > To what end? Except for EINIT, none of the ENCLS leafs are interesting
> > > from a permissions perspective. Trapping and re-executing ENCLS leafs
> > > is painful, e.g. most leafs have multiple virtual addresses that need to
> > > be translated. And routing everything through the regular interface
> > > would make SGX even slower than it already is, e.g. every ENCLS would
> > > take an additional ~900 cycles just to handle the VM-Exit, and that's
> > > not accounting for any additional overhead in the SGX code, e.g. using
> > > the regular interface would mean superfluous locks, etc...
> >
> > Trapping EINIT is what I have in mind.
>
> Phew, had me worried :-)
>
> > >
> > > Couldn't we require the same privilege/capability for VMs and and EINIT
> > > tokens? I.e. /dev/sgx/virtualmachine can only be opened by a user that
> > > can also generate tokens.
> >
> > Hmm, maybe. Or we can use Jarkko’s securityfs attribute thingy.
> >
> > Concretely, I think there are two things we care about:
> >
> > First, if the host enforces some policy as to which enclaves can
> > launch, then it should apply the same policy to guests — otherwise KVM
> > lets programs do an end run around the policy. So, in the initial
> > incarnation of this, QEMU should probably have to open the provision
> > attribute fd if it wants its guest to be able to EINIT a provisioning
> > enclave. When someone inevitably adds an EINIT LSM hook, the KVM
> > interface should also call it.
>
> Sort of. A guest that is running under KVM (i.e. VMX) is much more
> contained than a random userspace program. A rogue enclave in a VMX
> guest can attack the guest kernel/OS, but barring a bug (or more likely,
> several major bugs) elsewhere in the virtualization stack the enclave
> can't do anything nasty to the host. An enclave would let someone hide
> code, but enclaves are even more restricted than cpl3, i.e. there's not
> a lot it can do without coordinating with unencrypted code in the guest.
>
> And if someone has sufficient permissions to run a KVM guest, they're
> much more likely to do something malcious in the guest kernel, not an
> enclave.
Are you sure? On my laptop, /dev/kvm is 0666, and that's the distro
default. I don't think this is at all unusual. I'm not particularly
concerned about a guest attacking itself, but it's conceptually
straightforward to bypass whatever restrictions the host has by simply
opening /dev/kvm and sticking your enclave in a VM.
>
> All that aside, I don't see any justification for singling out SGX for
> extra scrutiny, there are other ways for a user with KVM permissions to
> hide malicious code in guest (and at cpl0!), e.g. AMD's SEV{-ES}.
I'm not singling out SGX. I'm just saying that the KVM should not
magically bypass host policy. If you want to assign a virtual
function on your NIC to a KVM guest, you need to give your QEMU
process that privilege. Similarly, if someone has a MAC policy that
controls which processes can launch which enclaves and they want to
run Windows with full SGX support in a VM guest, then they should
authorize that in their MAC policy by giving QEMU unrestricted launch
privileges.
Similarly, if access to a persistent provisioning identifier is
restricted, access to /dev/kvm shouldn't magically bypass it. Just
give the QEMU process the relevant privileges.
next prev parent reply other threads:[~2019-01-11 0:30 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-14 21:57 [RFC PATCH v5 0/5] x86: Add vDSO exception fixup for SGX Sean Christopherson
2018-12-14 21:57 ` [RFC PATCH v5 1/5] x86/vdso: Add support for exception fixup in vDSO functions Sean Christopherson
2018-12-14 21:57 ` [RFC PATCH v5 2/5] x86/fault: Add helper function to sanitize error code Sean Christopherson
2018-12-14 21:57 ` [RFC PATCH v5 3/5] x86/fault: Attempt to fixup unhandled #PF on ENCLU before signaling Sean Christopherson
2018-12-14 21:57 ` [RFC PATCH v5 4/5] x86/traps: Attempt to fixup exceptions in vDSO " Sean Christopherson
2018-12-14 21:57 ` [RFC PATCH v5 5/5] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions Sean Christopherson
2018-12-19 9:21 ` Jarkko Sakkinen
2018-12-18 4:18 ` [RFC PATCH v5 0/5] x86: Add vDSO exception fixup for SGX Jarkko Sakkinen
2018-12-18 15:08 ` Sean Christopherson
2018-12-19 4:43 ` Jarkko Sakkinen
2018-12-19 5:03 ` Jarkko Sakkinen
2018-12-19 7:58 ` x86/sgx: uapi change proposal Jarkko Sakkinen
2018-12-19 8:41 ` Jethro Beekman
2018-12-19 9:11 ` Jarkko Sakkinen
2018-12-19 9:36 ` Jethro Beekman
2018-12-19 10:43 ` Jarkko Sakkinen
2018-12-19 14:45 ` Sean Christopherson
2018-12-20 2:58 ` Andy Lutomirski
2018-12-20 10:32 ` Jarkko Sakkinen
2018-12-20 13:12 ` Jarkko Sakkinen
2018-12-20 13:19 ` Jarkko Sakkinen
2018-12-22 8:16 ` Jarkko Sakkinen
[not found] ` <20181222082502.GA13275@linux.intel.com>
2018-12-23 12:52 ` Jarkko Sakkinen
2018-12-23 20:42 ` Andy Lutomirski
2018-12-24 11:52 ` Jarkko Sakkinen
2019-01-02 20:47 ` Sean Christopherson
2019-01-03 15:02 ` Jarkko Sakkinen
[not found] ` <20190103162634.GA8610@linux.intel.com>
2019-01-09 14:45 ` Jarkko Sakkinen
2018-12-21 16:28 ` Sean Christopherson
2018-12-21 17:12 ` Andy Lutomirski
2018-12-21 18:24 ` Sean Christopherson
2018-12-21 23:41 ` Jarkko Sakkinen
2018-12-23 20:41 ` Andy Lutomirski
2018-12-24 12:01 ` Jarkko Sakkinen
2018-12-21 23:37 ` Jarkko Sakkinen
2018-12-22 6:32 ` Jarkko Sakkinen
2019-01-08 19:27 ` Huang, Kai
2019-01-08 22:09 ` Sean Christopherson
2019-01-08 22:54 ` Andy Lutomirski
2019-01-09 16:31 ` Sean Christopherson
2019-01-10 21:34 ` Andy Lutomirski
2019-01-10 22:22 ` Huang, Kai
2019-01-10 23:54 ` Sean Christopherson
2019-01-11 0:30 ` Andy Lutomirski [this message]
2019-01-11 1:32 ` Sean Christopherson
2019-01-11 12:58 ` Jarkko Sakkinen
2019-01-11 13:00 ` Jarkko Sakkinen
2019-01-11 23:19 ` Sean Christopherson
2019-01-18 14:37 ` Jarkko Sakkinen
2019-01-10 17:45 ` Jarkko Sakkinen
2019-01-10 21:36 ` Andy Lutomirski
2019-01-11 16:07 ` Jarkko Sakkinen
2019-01-09 5:24 ` Huang, Kai
2019-01-09 17:16 ` Sean Christopherson
2019-01-10 0:21 ` Huang, Kai
2019-01-10 0:40 ` Sean Christopherson
2019-01-10 17:43 ` Jarkko Sakkinen
2018-12-20 10:30 ` Jarkko Sakkinen
2018-12-19 14:43 ` Dr. Greg
2018-12-20 10:34 ` Jarkko Sakkinen
2018-12-20 22:06 ` Dr. Greg
2018-12-21 13:48 ` Jarkko Sakkinen
2018-12-20 12:08 ` Arnd Bergmann
2018-12-20 12:49 ` Jarkko Sakkinen
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