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From: Jethro Beekman <jethro@fortanix.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"dave.hansen@intel.com" <dave.hansen@intel.com>,
	"sean.j.christopherson@intel.com"
	<sean.j.christopherson@intel.com>,
	"nhorman@redhat.com" <nhorman@redhat.com>,
	"npmccallum@redhat.com" <npmccallum@redhat.com>,
	"serge.ayoun@intel.com" <serge.ayoun@intel.com>,
	"shay.katz-zamir@intel.com" <shay.katz-zamir@intel.com>,
	"haitao.huang@intel.com" <haitao.huang@intel.com>,
	"andriy.shevchenko@linux.intel.com" 
	<andriy.shevchenko@linux.intel.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"kai.svahn@intel.com" <kai.svahn@intel.com>,
	"bp@alien8.de" <bp@alien8.de>,
	"josh@joshtriplett.org" <josh@joshtriplett.org>,
	"luto@kernel.org" <luto@kernel.org>,
	"kai.huang@intel.com" <kai.huang@intel.com>,
	"rientjes@google.com" <rientjes@google.com>,
	"cedric.xing@intel.com" <cedric.xing@intel.com>
Subject: Re: [PATCH v21 18/28] x86/sgx: Add swapping code to the core and SGX driver
Date: Wed, 7 Aug 2019 06:33:32 +0000
Message-ID: <ba0aa229-d764-4e26-5de3-044fe28ddf61@fortanix.com> (raw)
In-Reply-To: <20190713170804.2340-19-jarkko.sakkinen@linux.intel.com>


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On 2019-07-13 10:07, Jarkko Sakkinen wrote:
> Because the kernel is untrusted, swapping pages in/out of the Enclave
> Page Cache (EPC) has specialized requirements:
> 
> * The kernel cannot directly access EPC memory, i.e. cannot copy data
>    to/from the EPC.
> * To evict a page from the EPC, the kernel must "prove" to hardware that
>    are no valid TLB entries for said page since a stale TLB entry would
>    allow an attacker to bypass SGX access controls.
> * When loading a page back into the EPC, hardware must be able to verify
>    the integrity and freshness of the data.
> * When loading an enclave page, e.g. regular pages and Thread Control
>    Structures (TCS), hardware must be able to associate the page with a
>    Secure Enclave Control Structure (SECS).
> 
> To satisfy the above requirements, the CPU provides dedicated ENCLS
> functions to support paging data in/out of the EPC:
> 
> * EBLOCK:   Mark a page as blocked in the EPC Map (EPCM).  Attempting
>              to access a blocked page that misses the TLB will fault.
> * ETRACK:   Activate blocking tracking.  Hardware verifies that all
>              translations for pages marked as "blocked" have been flushed
> 	    from the TLB.
> * EPA:      Add version array page to the EPC.  As the name suggests, a
>              VA page is an 512-entry array of version numbers that are
> 	    used to uniquely identify pages evicted from the EPC.
> * EWB:      Write back a page from EPC to memory, e.g. RAM.  Software
>              must supply a VA slot, memory to hold the a Paging Crypto
> 	    Metadata (PCMD) of the page and obviously backing for the
> 	    evicted page.
> * ELD{B,U}: Load a page in {un}blocked state from memory to EPC.  The
>              driver only uses the ELDU variant as there is no use case
> 	    for loading a page as "blocked" in a bare metal environment.
> 
> To top things off, all of the above ENCLS functions are subject to
> strict concurrency rules, e.g. many operations will #GP fault if two
> or more operations attempt to access common pages/structures.
> 
> To put it succinctly, paging in/out of the EPC requires coordinating
> with the SGX driver where all of an enclave's tracking resides.  But,
> simply shoving all reclaim logic into the driver is not desirable as
> doing so has unwanted long term implications:
> 
> * Oversubscribing EPC to KVM guests, i.e. virtualizing SGX in KVM and
>    swapping a guest's EPC pages (without the guest's cooperation) needs
>    the same high level flows for reclaim but has painfully different
>    semantics in the details.
> * Accounting EPC, i.e. adding an EPC cgroup controller, is desirable
>    as EPC is effectively a specialized memory type and even more scarce
>    than system memory.  Providing a single touchpoint for EPC accounting
>    regardless of end consumer greatly simplifies the EPC controller.
> * Allowing the userspace-facing driver to be built as a loaded module
>    is desirable, e.g. for debug, testing and development.  The cgroup
>    infrastructure does not support dependencies on loadable modules.
> * Separating EPC swapping from the driver once it has been tightly
>    coupled to the driver is non-trivial (speaking from experience).

Some of these points seem stale now.

--
Jethro Beekman | Fortanix


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  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-13 17:07 [PATCH v21 00/28] Intel SGX foundations Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 01/28] x86/cpufeatures: Add Intel-defined SGX feature bit Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 02/28] x86/cpufeatures: Add SGX sub-features (as Linux-defined bits) Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 03/28] x86/msr: Add IA32_FEATURE_CONTROL.SGX_ENABLE definition Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 04/28] x86/cpufeatures: Add Intel-defined SGX_LC feature bit Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 05/28] x86/msr: Add SGX Launch Control MSR definitions Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 06/28] x86/mm: x86/sgx: Add new 'PF_SGX' page fault error code bit Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 07/28] x86/mm: x86/sgx: Signal SIGSEGV for userspace #PFs w/ PF_SGX Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 08/28] x86/cpu/intel: Detect SGX support and update caps appropriately Jarkko Sakkinen
2019-07-24 19:35   ` Sean Christopherson
2019-08-02 20:48     ` Jarkko Sakkinen
2019-08-07 15:17     ` Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 09/28] x86/sgx: Add ENCLS architectural error codes Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 10/28] x86/sgx: Add SGX1 and SGX2 architectural data structures Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 11/28] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 12/28] x86/sgx: Enumerate and track EPC sections Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 13/28] x86/sgx: Add functions to allocate and free EPC pages Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 14/28] x86/sgx: Add sgx_einit() for initializing enclaves Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 15/28] mm: Introduce vm_ops->may_mprotect() Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 16/28] x86/sgx: Add the Linux SGX Enclave Driver Jarkko Sakkinen
2019-07-29 11:17   ` Ayoun, Serge
2019-08-07 15:15     ` Jarkko Sakkinen
2019-08-07 15:17       ` Jarkko Sakkinen
2019-08-07 16:45         ` Jethro Beekman
2019-08-08 15:40       ` Sean Christopherson
2019-08-09 15:02         ` Jarkko Sakkinen
2019-08-09 15:24           ` Sean Christopherson
2019-08-05 16:16   ` Sean Christopherson
2019-08-05 21:39     ` Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 17/28] x86/sgx: Add provisioning Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 18/28] x86/sgx: Add swapping code to the core and SGX driver Jarkko Sakkinen
2019-08-07  6:33   ` Jethro Beekman [this message]
2019-08-07 19:12     ` Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 19/28] x86/sgx: ptrace() support for the " Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 20/28] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 21/28] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 22/28] x86/traps: Attempt to fixup exceptions in vDSO before signaling Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 23/28] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions Jarkko Sakkinen
2019-07-17 22:07   ` Xing, Cedric
2019-07-13 17:08 ` [PATCH v21 24/28] selftests/x86: Add a selftest for SGX Jarkko Sakkinen
2019-07-17 22:37   ` Xing, Cedric
2019-08-02 20:46     ` Jarkko Sakkinen
2019-08-16 15:43     ` Jarkko Sakkinen
2019-08-16 15:51       ` Jarkko Sakkinen
2019-08-16 16:56     ` Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 25/28] x86/sgx: Update MAINTAINERS Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 26/28] docs: x86/sgx: Add Architecture documentation Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 27/28] docs: x86/sgx: Document kernel internals Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 28/28] docs: x86/sgx: Document the enclave API Jarkko Sakkinen
2019-07-14 14:36 ` [PATCH v21 00/28] Intel SGX foundations Jarkko Sakkinen
2019-08-07  6:40   ` Jethro Beekman

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