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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Cedric Xing <cedric.xing@intel.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	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, Jethro Beekman <jethro@fortanix.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	linux-sgx@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	nhorman@redhat.com, npmccallum@redhat.com,
	Serge Ayoun <serge.ayoun@intel.com>,
	Shay Katz-zamir <shay.katz-zamir@intel.com>,
	Haitao Huang <haitao.huang@intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Kai Svahn <kai.svahn@intel.com>, Borislav Petkov <bp@alien8.de>,
	Josh Triplett <josh@joshtriplett.org>,
	Kai Huang <kai.huang@intel.com>,
	David Rientjes <rientjes@google.com>,
	William Roberts <william.c.roberts@intel.com>,
	Philip Tricca <philip.b.tricca@intel.com>
Subject: Re: [RFC PATCH v2 1/5] mm: Introduce vm_ops->may_mprotect()
Date: Mon, 10 Jun 2019 08:55:49 -0700
Message-ID: <20190610155549.GB15995@linux.intel.com> (raw)
In-Reply-To: <20190610150600.GA3752@linux.intel.com>

On Mon, Jun 10, 2019 at 06:06:00PM +0300, Jarkko Sakkinen wrote:
> On Wed, Jun 05, 2019 at 07:11:41PM -0700, Sean Christopherson wrote:
> > SGX will use the may_mprotect() hook to prevent userspace from
> > circumventing various security checks, e.g. Linux Security Modules.
> > Naming it may_mprotect() instead of simply mprotect() is intended to
> > reflect the hook's purpose as a way to gate mprotect() as opposed to
> > a wholesale replacement.
> 
> "This commit adds may_mprotect() to struct vm_operations_struct, which
> can be used to ask from the owner of a VMA if mprotect() is allowed."
> 
> This would be more appropriate statement because that is what the code
> change aims for precisely. I did not even understand what you meant by
> gating in this context. I would leave SGX and LSM's (and especially
> "various security checks", which means abssolutely nothing) out of the
> first paragraph completely.
> 
> > Enclaves are built by copying data from normal memory into the Enclave
> > Page Cache (EPC).  Due to the nature of SGX, the EPC is represented by a
> > single file that must be MAP_SHARED, i.e. mprotect() only ever sees a
> > MAP_SHARED vm_file that references single file path.  Furthermore, all
> > enclaves will need read, write and execute pages in the EPC.
> 
> I would just say that "Due to the fact that EPC is delivered as IO
> memory from the preboot firmware, it can be only mapped as MAP_SHARED".
> It is what it is.

I was trying to convey that the nature of SGX itself requires that an
enclave's pages are shared between process.  E.g. {MAP,VM}_SHARED would be
required even if we modified the mmu to handle EPC memory in such a way
that it didn't have to be tagged with VM_PFNMAP.

> > As a result, LSM policies cannot be meaningfully applied, e.g. an LSM
> > can deny access to the EPC as a whole, but can't deny PROT_EXEC on page
> > that originated in a non-EXECUTE file (which is long gone by the time
> > mprotect() is called).
> 
> I have hard time following what is paragraph is trying to say.
> 
> > By hooking mprotect(), SGX can make explicit LSM upcalls while an
> > enclave is being built, i.e. when the kernel has a handle to origin of
> > each enclave page, and enforce the result of the LSM policy whenever
> > userspace maps the enclave page in the future.
> 
> "LSM policy whenever calls mprotect()"? I'm no sure why you mean by
> mapping here and if there is any need to talk about future. Isn't this
> needed now?

Future is referring to the timeline of a running kernel, not the future
of the kernel code.

Rather than trying to explain all of the above with words, I'll provide
code examples to show how ->may_protect() will be used by SGX and why it
is the preferred solution.

> > Alternatively, SGX could play games with MAY_{READ,WRITE,EXEC}, but
> > that approach is quite ugly, e.g. would require userspace to call an
> > SGX ioctl() prior to using mprotect() to extend a page's protections.
> 
> Instead of talking "playing games" I would state what could be done with
> VM_MAY{READ,WRITE,EXEC} and why it is bad. Leaves questions otherwise.
> 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  include/linux/mm.h |  2 ++
> >  mm/mprotect.c      | 15 +++++++++++----
> >  2 files changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 0e8834ac32b7..a697996040ac 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -458,6 +458,8 @@ struct vm_operations_struct {
> >  	void (*close)(struct vm_area_struct * area);
> >  	int (*split)(struct vm_area_struct * area, unsigned long addr);
> >  	int (*mremap)(struct vm_area_struct * area);
> > +	int (*may_mprotect)(struct vm_area_struct * area, unsigned long start,
> > +			    unsigned long end, unsigned long prot);
> 
> Could be just boolean.
> 
> /Jarkko

  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 [this message]
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
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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