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From: Stephen Smalley <sds@tycho.nsa.gov>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Xing, Cedric" <cedric.xing@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Paul Moore <paul@paul-moore.com>,
	Eric Paris <eparis@parisplace.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Jethro Beekman <jethro@fortanix.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Dr. Greg" <greg@enjellic.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"nhorman@redhat.com" <nhorman@redhat.com>,
	"npmccallum@redhat.com" <npmccallum@redhat.com>,
	"Ayoun, Serge" <serge.ayoun@intel.com>,
	"Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
	"Huang, Haitao" <haitao.huang@intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	"Svahn, Kai" <kai.svahn@intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Josh Triplett <josh@joshtriplett.org>,
	"Huang, Kai" <kai.huang@intel.com>,
	David Rientjes <rientjes@google.com>
Subject: Re: SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)
Date: Fri, 17 May 2019 12:37:40 -0400	[thread overview]
Message-ID: <80013cca-f1c2-f4d5-7558-8f4e752ada76@tycho.nsa.gov> (raw)
In-Reply-To: <ca807220-47e2-5ec2-982c-4fb4a72439c6@tycho.nsa.gov>

On 5/17/19 12:20 PM, Stephen Smalley wrote:
> On 5/17/19 11:09 AM, Sean Christopherson wrote:
>> On Fri, May 17, 2019 at 09:53:06AM -0400, Stephen Smalley wrote:
>>> On 5/16/19 6:23 PM, Xing, Cedric wrote:
>>>> I thought EXECMOD applied to files (and memory mappings backed by 
>>>> them) but
>>>> I was probably wrong. It sounds like EXECMOD applies to the whole 
>>>> process so
>>>> would allow all pages within a process's address space to be 
>>>> modified then
>>>> executed, regardless the backing files. Am I correct this time?
>>>
>>> No, you were correct the first time I think; EXECMOD is used to control
>>> whether a process can make executable a private file mapping that has
>>> previously been modified (e.g. text relocation); it is a special case to
>>> support text relocations without having to allow full EXECMEM (i.e. 
>>> execute
>>> arbitrary memory).
>>>
>>> SELinux checks relevant to W^X include:
>>>
>>> - EXECMEM: mmap/mprotect PROT_EXEC an anonymous mapping (regardless of
>>> PROT_WRITE, since we know the content has to have been written at some
>>> point) or a private file mapping that is also PROT_WRITE.
>>> - EXECMOD: mprotect PROT_EXEC a private file mapping that has been
>>> previously modified, typically for text relocations,
>>> - FILE__WRITE: mmap/mprotect PROT_WRITE a shared file mapping,
>>> - FILE__EXECUTE: mmap/mprotect PROT_EXEC a file mapping.
>>>
>>> (ignoring EXECSTACK and EXECHEAP here since they aren't really 
>>> relevant to
>>> this discussion)
>>>
>>> So if you want to ensure W^X, then you wouldn't allow EXECMEM for the
>>> process, EXECMOD by the process to any file, and the combination of both
>>> FILE__WRITE and FILE__EXECUTE by the process to any file.
>>>
>>> If the /dev/sgx/enclave mappings are MAP_SHARED and you aren't using an
>>> anonymous inode, then I would expect that only the FILE__WRITE and
>>> FILE__EXECUTE checks are relevant.
>>
>> Yep, I was just typing this up in a different thread:
>>
>> I think we may want to change the SGX API to alloc an anon inode for each
>> enclave instead of hanging every enclave off of the /dev/sgx/enclave 
>> inode.
>> Because /dev/sgx/enclave is NOT private, SELinux's file_map_prot_check()
>> will only require FILE__WRITE and FILE__EXECUTE to mprotect() enclave 
>> VMAs
>> to RWX.  Backing each enclave with an anon inode will make SELinux treat
>> EPC memory like anonymous mappings, which is what we want (I think), e.g.
>> making *any* EPC page executable will require PROCESS__EXECMEM (SGX is
>> 64-bit only at this point, so SELinux will always have default_noexec).
> 
> I don't think we want to require EXECMEM (or equivalently both 
> FILE__WRITE and FILE__EXECUTE to /dev/sgx/enclave) for making any EPC 
> page executable, only if the page is also writable or previously 
> modified.  The intent is to prevent arbitrary code execution without 
> EXECMEM (or FILE__WRITE|FILE__EXECUTE), while still allowing enclaves to 
> be created without EXECMEM as long as the EPC page mapping is only ever 
> mapped RX and its initial contents came from an unmodified file mapping 
> that was PROT_EXEC (and hence already checked via FILE__EXECUTE).

Also, just to be clear, there is nothing inherently better about 
checking EXECMEM instead of checking both FILE__WRITE and FILE__EXECUTE 
to the /dev/sgx/enclave inode, so I wouldn't switch to using anon inodes 
for that reason.  Using anon inodes also unfortunately disables SELinux 
inode-based checking since we no longer have any useful inode 
information, so you'd lose out on SELinux ioctl whitelisting on those 
enclave inodes if that matters.

  parent reply	other threads:[~2019-05-17 16:38 UTC|newest]

Thread overview: 127+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <8fe520bb-30bd-f246-a3d8-c5443e47a014@intel.com>
     [not found] ` <358e9b36-230f-eb18-efdb-b472be8438b4@fortanix.com>
     [not found]   ` <960B34DE67B9E140824F1DCDEC400C0F4E886094@ORSMSX116.amr.corp.intel.com>
     [not found]     ` <6da269d8-7ebb-4177-b6a7-50cc5b435cf4@fortanix.com>
     [not found]       ` <CALCETrWCZQwg-TUCm58DVG43=xCKRsMe1tVHrR8vdt06hf4fWA@mail.gmail.com>
     [not found]         ` <20190513102926.GD8743@linux.intel.com>
     [not found]           ` <20190514104323.GA7591@linux.intel.com>
     [not found]             ` <CALCETrVbgTCnPo=PAq0-KoaRwt--urrPzn==quAJ8wodCpkBkw@mail.gmail.com>
     [not found]               ` <20190514204527.GC1977@linux.intel.com>
     [not found]                 ` <CALCETrX6aL367mMJh5+Y1Seznfu-AvhPV6P7GkWF4Dhu0GV8cw@mail.gmail.com>
     [not found]                   ` <20190515013031.GF1977@linux.intel.com>
2019-05-15 18:27                     ` SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support) Andy Lutomirski
2019-05-15 19:58                       ` James Morris
2019-05-15 20:35                         ` Andy Lutomirski
2019-05-15 22:46                           ` James Morris
2019-05-15 23:13                             ` Andy Lutomirski
2019-05-16  3:03                               ` Xing, Cedric
2019-05-16  4:40                                 ` Andy Lutomirski
2019-05-16 22:23                                   ` Xing, Cedric
2019-05-17  0:35                                     ` Andy Lutomirski
2019-05-17  1:06                                       ` Xing, Cedric
2019-05-17  1:21                                         ` Andy Lutomirski
2019-05-17 16:05                                       ` Sean Christopherson
2019-05-17 13:53                                     ` Stephen Smalley
2019-05-17 15:09                                       ` Sean Christopherson
2019-05-17 16:20                                         ` Stephen Smalley
2019-05-17 16:24                                           ` Andy Lutomirski
2019-05-17 16:37                                           ` Stephen Smalley [this message]
2019-05-17 17:12                                             ` Andy Lutomirski
2019-05-17 18:05                                               ` Stephen Smalley
2019-05-17 19:20                                                 ` Stephen Smalley
2019-05-17 19:28                                                 ` Sean Christopherson
2019-05-17 20:09                                                   ` Stephen Smalley
2019-05-17 20:14                                                     ` Andy Lutomirski
2019-05-17 20:34                                                       ` Stephen Smalley
2019-05-17 21:36                                                     ` Sean Christopherson
2019-05-17 17:29                                             ` Sean Christopherson
2019-05-17 17:42                                               ` Stephen Smalley
2019-05-17 17:50                                                 ` Sean Christopherson
2019-05-17 18:16                                                   ` Stephen Smalley
2019-05-17 17:43                                               ` Andy Lutomirski
2019-05-17 17:55                                                 ` Sean Christopherson
2019-05-17 18:04                                                   ` Linus Torvalds
2019-05-17 18:21                                                     ` Sean Christopherson
2019-05-17 18:33                                                       ` Linus Torvalds
2019-05-17 18:52                                                         ` Sean Christopherson
2019-05-17 18:53                                                       ` Andy Lutomirski
2019-05-16  7:24                               ` James Morris
2019-05-16 21:00                                 ` Andy Lutomirski
2019-05-20  9:38                                 ` Dr. Greg
2019-05-15 21:38                       ` Sean Christopherson
2019-05-16  1:19                         ` Haitao Huang
2019-05-16  5:16                       ` Jarkko Sakkinen
2019-05-16 21:02                         ` Andy Lutomirski
2019-05-16 22:45                           ` Sean Christopherson
2019-05-16 23:29                             ` Xing, Cedric
2019-05-20 11:29                             ` Jarkko Sakkinen
2019-05-20 11:33                           ` Jarkko Sakkinen
2019-05-17  0:03                       ` Sean Christopherson
2019-05-17  0:26                         ` Andy Lutomirski
2019-05-17 15:41                           ` Sean Christopherson
2019-05-20 11:42                             ` Jarkko Sakkinen
2019-05-20 11:41                           ` Jarkko Sakkinen
2019-05-21 15:19                             ` Jarkko Sakkinen
2019-05-21 15:24                               ` Jethro Beekman
2019-05-22 13:10                                 ` Jarkko Sakkinen
2019-05-21 15:51                               ` Sean Christopherson
2019-05-22 13:20                                 ` Jarkko Sakkinen
2019-05-22 13:22                                   ` Jarkko Sakkinen
2019-05-22 13:56                                     ` Stephen Smalley
2019-05-22 15:38                                       ` Sean Christopherson
2019-05-22 22:42                                         ` Andy Lutomirski
2019-05-23  2:35                                           ` Sean Christopherson
2019-05-23 10:26                                             ` Jarkko Sakkinen
2019-05-23 14:17                                               ` Sean Christopherson
2019-05-23 15:38                                                 ` Andy Lutomirski
2019-05-23 23:40                                                   ` Sean Christopherson
2019-05-24  1:17                                                     ` Andy Lutomirski
2019-05-24  7:24                                                       ` Xing, Cedric
2019-05-24 15:41                                                         ` Stephen Smalley
2019-05-24 16:57                                                           ` Xing, Cedric
2019-05-24 17:42                                                           ` Sean Christopherson
2019-05-24 17:54                                                             ` Andy Lutomirski
2019-05-24 17:56                                                               ` Sean Christopherson
2019-05-24 17:54                                                             ` Sean Christopherson
2019-05-24 18:34                                                               ` Xing, Cedric
2019-05-24 19:13                                                                 ` Sean Christopherson
2019-05-24 19:30                                                                   ` Andy Lutomirski
2019-05-24 20:42                                                                   ` Xing, Cedric
2019-05-24 21:11                                                                     ` Sean Christopherson
2019-05-24 19:37                                                                 ` Andy Lutomirski
2019-05-24 20:03                                                                   ` Sean Christopherson
2019-05-24 20:58                                                                     ` Xing, Cedric
2019-05-24 21:27                                                                     ` Andy Lutomirski
2019-05-24 22:41                                                                       ` Sean Christopherson
2019-05-24 23:42                                                                         ` Andy Lutomirski
2019-05-25 22:40                                                                           ` Xing, Cedric
2019-05-26  0:57                                                                             ` Andy Lutomirski
2019-05-26  6:09                                                                               ` Xing, Cedric
2019-05-28 20:24                                                                                 ` Sean Christopherson
2019-05-28 20:48                                                                                   ` Andy Lutomirski
2019-05-28 21:41                                                                                     ` Sean Christopherson
2019-05-30  5:38                                                                                       ` Xing, Cedric
2019-05-30 17:21                                                                                         ` Sean Christopherson
2019-05-29 14:08                                                                                   ` Stephen Smalley
2019-05-30  6:12                                                                                     ` Xing, Cedric
2019-05-30 14:22                                                                                       ` Stephen Smalley
2019-05-30 14:31                                                                                         ` Andy Lutomirski
2019-05-30 15:04                                                                                           ` Stephen Smalley
2019-05-30 16:14                                                                                             ` Andy Lutomirski
2019-05-30 18:01                                                                                               ` Sean Christopherson
2019-05-30 19:20                                                                                                 ` Andy Lutomirski
2019-05-30 21:16                                                                                                   ` Sean Christopherson
2019-05-30 21:23                                                                                                     ` Andy Lutomirski
2019-05-30 21:36                                                                                                       ` Sean Christopherson
2019-06-03  9:12                                                                                                         ` Dr. Greg
2019-06-03 21:08                                                                                                         ` Jarkko Sakkinen
2019-05-30 21:48                                                                                                   ` Xing, Cedric
2019-05-30 22:24                                                                                                     ` Sean Christopherson
2019-06-03 21:05                                                                                                 ` Jarkko Sakkinen
2019-06-03 20:54                                                                                               ` Jarkko Sakkinen
2019-06-03 21:23                                                                                                 ` Sean Christopherson
2019-06-04 11:39                                                                                                   ` Jarkko Sakkinen
2019-06-03 21:37                                                                                                 ` Andy Lutomirski
2019-06-03 20:47                                                                                             ` Jarkko Sakkinen
2019-06-03 20:43                                                                                           ` Jarkko Sakkinen
2019-05-25 17:31                                                                     ` Dr. Greg
2019-05-24 16:43                                                         ` Andy Lutomirski
2019-05-24 17:07                                                           ` Sean Christopherson
2019-05-24 17:51                                                             ` Andy Lutomirski
2019-05-24 14:44                                                   ` Stephen Smalley
2019-05-27 13:48                                                   ` Jarkko Sakkinen
2019-05-23 19:58                                                 ` Sean Christopherson
2019-05-27 13:34                                                 ` Jarkko Sakkinen
2019-05-27 13:38                                                   ` Jarkko Sakkinen
2019-05-23  8:10                                           ` Jarkko Sakkinen
2019-05-23  8:23                                             ` Jarkko Sakkinen
2019-05-20 11:36                         ` Jarkko Sakkinen

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