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From: "Xing, Cedric" <cedric.xing@intel.com>
To: Stephen Smalley <sds@tycho.nsa.gov>,
	"Christopherson, Sean J" <sean.j.christopherson@intel.com>
Cc: "linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
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	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	"jarkko.sakkinen@linux.intel.com"
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	"luto@kernel.org" <luto@kernel.org>,
	"jmorris@namei.org" <jmorris@namei.org>,
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	"Ayoun, Serge" <serge.ayoun@intel.com>,
	"Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
	"Huang, Haitao" <haitao.huang@intel.com>,
	"andriy.shevchenko@linux.intel.com" 
	<andriy.shevchenko@linux.intel.com>,
	"Svahn, Kai" <kai.svahn@intel.com>, "bp@alien8.de" <bp@alien8.de>,
	"josh@joshtriplett.org" <josh@joshtriplett.org>,
	"Huang, Kai" <kai.huang@intel.com>,
	"rientjes@google.com" <rientjes@google.com>,
	"Roberts, William C" <william.c.roberts@intel.com>,
	"Tricca, Philip B" <philip.b.tricca@intel.com>
Subject: RE: [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux
Date: Thu, 13 Jun 2019 23:03:24 +0000
Message-ID: <960B34DE67B9E140824F1DCDEC400C0F65503EDD@ORSMSX116.amr.corp.intel.com> (raw)
In-Reply-To: <8d99d8fb-a921-286a-8cf0-cd522e09b37c@tycho.nsa.gov>

> From: Stephen Smalley [mailto:sds@tycho.nsa.gov]
> Sent: Thursday, June 13, 2019 10:02 AM
> 
> On 6/11/19 6:02 PM, Sean Christopherson wrote:
> > On Tue, Jun 11, 2019 at 09:40:25AM -0400, Stephen Smalley wrote:
> >> I haven't looked at this code closely, but it feels like a lot of
> >> SGX-specific logic embedded into SELinux that will have to be
> >> repeated or reused for every security module.  Does SGX not track
> this state itself?
> >
> > SGX does track equivalent state.
> >
> > There are three proposals on the table (I think):
> >
> >    1. Require userspace to explicitly specificy (maximal) enclave page
> >       permissions at build time.  The enclave page permissions are
> provided
> >       to, and checked by, LSMs at enclave build time.
> >
> >       Pros: Low-complexity kernel implementation, straightforward
> auditing
> >       Cons: Sullies the SGX UAPI to some extent, may increase
> complexity of
> >             SGX2 enclave loaders.
> >
> >    2. Pre-check LSM permissions and dynamically track mappings to
> enclave
> >       pages, e.g. add an SGX mprotect() hook to restrict W->X and WX
> >       based on the pre-checked permissions.
> >
> >       Pros: Does not impact SGX UAPI, medium kernel complexity
> >       Cons: Auditing is complex/weird, requires taking enclave-
> specific
> >             lock during mprotect() to query/update tracking.
> >
> >    3. Implement LSM hooks in SGX to allow LSMs to track enclave
> regions
> >       from cradle to grave, but otherwise defer everything to LSMs.
> >
> >       Pros: Does not impact SGX UAPI, maximum flexibility, precise
> auditing
> >       Cons: Most complex and "heaviest" kernel implementation of the
> three,
> >             pushes more SGX details into LSMs.
> >
> > My RFC series[1] implements #1.  My understanding is that Andy
> > (Lutomirski) prefers #2.  Cedric's RFC series implements #3.
> >
> > Perhaps the easiest way to make forward progress is to rule out the
> > options we absolutely *don't* want by focusing on the potentially
> > blocking issue with each option:
> >
> >    #1 - SGX UAPI funkiness
> >
> >    #2 - Auditing complexity, potential enclave lock contention
> >
> >    #3 - Pushing SGX details into LSMs and complexity of kernel
> > implementation
> >
> >
> > [1]
> > https://lkml.kernel.org/r/20190606021145.12604-1-sean.j.christopherson
> > @intel.com
> 
> Given the complexity tradeoff, what is the clear motivating example for
> why #1 isn't the obvious choice? That the enclave loader has no way of
> knowing a priori whether the enclave will require W->X or WX?  But
> aren't we better off requiring enclaves to be explicitly marked as
> needing such so that we can make a more informed decision about whether
> to load them in the first place?

Are you asking this question at a) page granularity, b) file granularity or c) enclave (potentially comprised of multiple executable files) granularity?

#b is what we have on regular executable files and shared objects (i.e. FILE__EXECMOD). We all know how to do that.

#c is kind of new but could be done via some proxy file (e.g. sigstruct file) hence reduced to #b.

#a is problematic. It'd require compilers/linkers to generate such information, and proper executable image file format to carry that information, to be eventually picked up the loader. SELinux doesn't have PAGE__EXECMOD I guess is because it is generally considered impractical.

Option #1 however requires #a because the driver doesn't track which page was loaded from which file, otherwise it can no longer be qualified "simple". Or we could just implement #c, which will make all options simpler. But I guess #b is still preferred, to be aligned with what SELinux is enforcing today on regular memory pages.

  reply index

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-06  2:11 [RFC PATCH v2 0/5] security: x86/sgx: SGX vs. LSM Sean Christopherson
2019-06-06  2:11 ` [RFC PATCH v2 1/5] mm: Introduce vm_ops->may_mprotect() Sean Christopherson
2019-06-10 15:06   ` Jarkko Sakkinen
2019-06-10 15:55     ` Sean Christopherson
2019-06-10 17:47       ` Xing, Cedric
2019-06-10 19:49         ` Sean Christopherson
2019-06-10 22:06           ` Xing, Cedric
2019-06-06  2:11 ` [RFC PATCH v2 2/5] x86/sgx: Require userspace to define enclave pages' protection bits Sean Christopherson
2019-06-10 15:27   ` Jarkko Sakkinen
2019-06-10 16:15     ` Sean Christopherson
2019-06-10 17:45       ` Jarkko Sakkinen
2019-06-10 18:17         ` Sean Christopherson
2019-06-12 19:26           ` Jarkko Sakkinen
2019-06-10 18:29   ` Xing, Cedric
2019-06-10 19:15     ` Andy Lutomirski
2019-06-10 22:28       ` Xing, Cedric
2019-06-12  0:09         ` Andy Lutomirski
2019-06-12 14:34           ` Sean Christopherson
2019-06-12 18:20             ` Xing, Cedric
2019-06-06  2:11 ` [RFC PATCH v2 3/5] x86/sgx: Enforce noexec filesystem restriction for enclaves Sean Christopherson
2019-06-10 16:00   ` Jarkko Sakkinen
2019-06-10 16:44     ` Andy Lutomirski
2019-06-11 17:21       ` Stephen Smalley
2019-06-06  2:11 ` [RFC PATCH v2 4/5] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX Sean Christopherson
2019-06-07 19:58   ` Stephen Smalley
2019-06-10 16:21     ` Sean Christopherson
2019-06-10 16:05   ` Jarkko Sakkinen
2019-06-06  2:11 ` [RFC PATCH v2 5/5] security/selinux: Add enclave_load() implementation Sean Christopherson
2019-06-07 21:16   ` Stephen Smalley
2019-06-10 16:46     ` Sean Christopherson
2019-06-17 16:38   ` Jarkko Sakkinen
2019-06-10  7:03 ` [RFC PATCH v1 0/3] security/x86/sgx: SGX specific LSM hooks Cedric Xing
2019-06-10  7:03   ` [RFC PATCH v1 1/3] LSM/x86/sgx: Add " Cedric Xing
2019-06-10  7:03   ` [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux Cedric Xing
2019-06-11 13:40     ` Stephen Smalley
2019-06-11 22:02       ` Sean Christopherson
2019-06-12  9:32         ` Dr. Greg
2019-06-12 14:25           ` Sean Christopherson
2019-06-13  7:25             ` Dr. Greg
2019-06-12 19:30         ` Andy Lutomirski
2019-06-12 22:02           ` Sean Christopherson
2019-06-13  0:10             ` Xing, Cedric
2019-06-13  1:02             ` Xing, Cedric
2019-06-13 17:02         ` Stephen Smalley
2019-06-13 23:03           ` Xing, Cedric [this message]
2019-06-13 23:17             ` Sean Christopherson
2019-06-14  0:31               ` Xing, Cedric
2019-06-14  0:46           ` Sean Christopherson
2019-06-14 15:38             ` Sean Christopherson
2019-06-16 22:14               ` Andy Lutomirski
2019-06-17 16:49                 ` Sean Christopherson
2019-06-17 17:08                   ` Andy Lutomirski
2019-06-18 15:40                   ` Dr. Greg
2019-06-14 17:16             ` Xing, Cedric
2019-06-14 17:45               ` Sean Christopherson
2019-06-14 17:53                 ` Sean Christopherson
2019-06-14 20:01                   ` Sean Christopherson
2019-06-16 22:16               ` Andy Lutomirski
2019-06-14 23:19             ` Dr. Greg
2019-06-11 22:55       ` Xing, Cedric
2019-06-13 18:00         ` Stephen Smalley
2019-06-13 19:48           ` Sean Christopherson
2019-06-13 21:09             ` Xing, Cedric
2019-06-13 21:02           ` Xing, Cedric
2019-06-14  0:37           ` Sean Christopherson
2019-06-10  7:03   ` [RFC PATCH v1 3/3] LSM/x86/sgx: Call new LSM hooks from SGX subsystem Cedric Xing
2019-06-10 17:36   ` [RFC PATCH v1 0/3] security/x86/sgx: SGX specific LSM hooks Jarkko Sakkinen

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