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** Quote generation daemon - assists QEMU in acquiring signed attestation reports for TDX VMs.
** Quote generation daemon - assists QEMU in acquiring signed attestation reports for TDX VMs.


=== Enclave use cases ===
The code and binaries related to the host OS platform components will be installed in the normal filesystem locations common to all Fedora packages.


At a high level, SGX enclaves provide a way to run code in a secure, encrypted & isolated execution context, free from manipulation by any other software component on the machine, aside from DoS attacks.
For the purposes of packaging, the enclaves will be treated as cross-compilation target. While the build architecture is x86_64, the runtime has custom C / C++ libraries that must be used, and separate code loader.  


There are manways
With this in mind, all enclave related code and binaries are proposed to be installed at '''/usr/x86_64-intel-sgx''', specifically under ''lib64'' and ''include'' sub-directories.


==== Compatibility with Fedora mission for software & content freedom ====
The generated binary packages will generally all have an 'sgx-' prefix to their name, with enclave related packages having an more specialized 'sgx-enclave-' name prefix.


When dealing with cryptographically attested software, it is important to consider '''whom is benefitting''' from verifying the execution context. There are generally three parties involved in such software
== Feedback ==


* '''Providing party''' - the organization or individual that is signing the software being used. This could be the original software author/vendor, or an intermediary such as a Linux distributor.
* '''Deploying party''' - the organization or individual that is running the software in question. This could be a so called 'end user', or it could be a service provider running something on their behalf.
* '''Verifying party''' - the organization or individual that is relying on verification of the executed software. This could be the so called 'end user', but it could be a 3rd party attempting to place constraints on usage (e.g. DRM)


The Fedora missions states 
== Benefit to Fedora ==
As a general purpose infrastructure technology, SGX can be applied to / used by a wide variety of scenarios / applications.


  We are dedicated to free software and content.  
The primary goal in introducing SGX into Fedora, however, is to support the Fedora KVM virtualization stack when it introduces confidential virtual machines running with Intel TDX. The TDX attestation implementation in currently integrated with Intel CPUs is built on the SGX technology. Attestation is the means by which a guest VM owner, can prove that their VM machine is running in confidential mode on genuine Intel hardware, as opposed to being in "blue pill" environment.
  Advancing software and content freedom is a  
  central community goal, which we accomplish
  through the software and content we promote.


In all cases, Intel acts as a "verifying party" when a platform is deployed or provisioned, when the platform owner requests a certificate to prove their hardware is authentic. This is a low level a bootstrapping task, to enable higher level use of SGX. Thus while Intel is the verifying party at a low level, the ultimate beneficiary is determined by the higher level usage of SGX who is also a verifying party.
== Scope ==
=== Proposal owners===


Thus, while this low level usage has some impact on software freedom, it is limited to the minimum required to bootstrap use of the SGX technology. This is on a par with how firmware, or CPU microcode, binaries must have valid signatures to bootstrap use of the platform
Add at least the following source packages to Fedora:


* '''CppMicroServices''' - a C++ runtime library for building microservices daemons
* '''sgx-srpm-macros''' - define some common macros for where SGX content will live in the filesystem tree
* '''linux-sgx''' - provide the SGX platform development headers & libraries, runtime libraries, and supporting daemons


Assuming that pre-built, signed SGX architectural enclaves will be shipped, the following additional package is proposed:


Use of SGX as a DRM mechanism in BluRay playback software is not benefit for the user of the player, as it constrains the scenarios in which they can consume the content. The beneficiary is a 3rd party organization seeking to control the end user. Such use of SGX enclaves which compromise either software or contet freedom should be considered incompatible with Fedora's mission for end user freedom and thus not permitted.
* '''linux-sgx-enclavesXXX''' - one (or more) packages containing architectural enclaves


Use of SGX as a mechanism for proving the integrity of a virtual machine has multiple beneficiaries. The Fedora user who owns the hypervisor OS install benefits in being able to prove integrity of the service they provide. Where the virtual machine is running Fedora as its OS, the Fedora user of the VM further benefits in being able to prove integrity of their guest OS. Including enclaves needed to attest TDX is generally compatible with Fedora's mission. The owners of the host & guest OS, gets to decide the usage policy and thus are not constraining their own software and content freedom. This usage of SGX is compatible with Fedora's mission for end user freeom and thus should be permitted.
Not every architectural enclave binary is re-issued on every release. New signed builds are only made available when there is a CVE fix, or a feature enhancement. At time of writing the SGX 2.25 release included new builds for every enclave. A future 2.26 release may only update a subset. Hence at some points in time, Fedora may have more than one '''linux-sgx-encalvesXXX''' package present.


=== Enclaves in depth vs packaging & licensing guidelines ===
If it is required to perform a reproducible build of the above architectural enclave binaries, to prove the binaries match the claimed sources, the following toolchain packages are needed:


Generally Fedora requires all software to be fully built from source, with the complete & corresponding source made available under one of the permitted code licenses.
* '''sgx-compat-gccXXX''' - one (or more) '''specific''' GCC versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-binutilsXXX''' - one (or more) '''specific''' binutils versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-nasmXXX''' - one (or more) '''specific''' NASM versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-glibc-headersXXX''' - one (or more) '''specific''' GCC versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-kernel-headersXXX''' - one (or more) '''specific''' GCC versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.


There is, however, an exception for firmware binaries which do not have to provide source, and merely required to permit free redistribution.
At time of writing, with the SGX 2.25 release, the versions required to perform a fully reproducible build will be


The question is how to treat enclaves, and deciding this requires understanding what SGX enclaves are and how they are used.
* '''gcc''': 8.5.0, 9.5.0
* '''binutils''': 2.38, 2.40
* '''nasm''': 2.16.01
* '''glibc''': 2.38
* '''kernel''': 5.17


==== Enclaves as a new platform build target ====
Note, while Fedora already ships builds fo gcc, binutils, etc, performing reproducible builds requires specific versions, configured with particular choice of build options. Hence the intention to ship parallel packages, which are '''exclusively''' intended for use in reproducing enclaves. There will be no support for using these toolchain packages for any other situation in Fedora.


SGX enclaves are compiled to x86 machine code from C/C++ source, using custom C/C++ runtime libraries, instead of the host OS glibc / libstdc++. IOW, while the enclaves can build with the existing x86 C/C++ toolchain, they are more like a cross-compilation target in the way that a separate non-Linux runtime is used.
Note: the fact that two versions are needed for binutils and GCC, is an upstream [https://github.com/intel/linux-sgx/issues/1045 an upstream bug]


The resulting SGX enclave binary uses the ELF format, creating ELF executables, albeit with a '''.so''' file suffix. While the executable binary does have a '''.interp''' ELF section, the referenced '''ld-linux.so''' cannot load an enclave. A specialized SGX host OS library must be called to create an enclave and load code into it. Given that, the '''.interp''' ELF section is in fact redundant and misleading, and has [https://github.com/intel/linux-sgx/pull/1061 been proposed for removal].
Note: the enclaves are supposed to be built exclusively against the SGX SDK which provides its own C runtime headers. Thus the fact that it has a requirement for header files from glibc & kernel is also [https://github.com/intel/linux-sgx/pull/1062 likely another upstream bug].
The full set of proposed source RPMs and their corresponding binary RPM outputs can be see from Copr:


To load an SGX enclave, the ELF binary must have an embedded signature, that is created by the '''sgx_sign''' tool, using signing keys provided by whomever is going to attest to trustworthiness of the enclave binary. The signer can be whomever authors the enclave, but in most cases, can also be an arbitrary third party.
https://copr.fedorainfracloud.org/coprs/berrange/sgx-ng/monitor/


The critical point is that whomever is going to later verify the SGX enclave must be willing to trust whomever signed it. Such a trust relationship decision is dependent on the usage context of the enclave in question.
Note, the pre-built, signed architectural enclaves are not always re-created on each SGX release.


==== Enclave usage classes ====
=== Other developers===


Broadly speaking there are considered to be two classes of enclave:
It is not anticipated that other package maintainers need do anything to support introduction of SGX. The kernel is already built with the SGX feature enabled.


# '''Architectural enclaves''' - these are a small set of common enclaves, created and signed by Intel, which ship as standard in any SGX deployment. They provide a hardware enablement role, bootstrapping the cryptographic root of trust on a platform.
systemd ships with udev rules to enable creation of some of the required device nodes. The SGX package contains addon udev rules for remaining device nodes. The latter may be contributed upstream to systemd in future, and would flow back into Fedora in a normal systemd update.
# '''Application enclaves''' - this is an arbitrary set of custom enclaves, written by independent software vendors / providers to perform application specific tasks. They are signed by whichever party is to be relied upon to validate trustworthiness of the enclave code.


Both architectural and application enclaves are built and deployed in the same way, using the same runtime libraries. Their difference is largely where they sit in the chain of trust, with architectural enclaves being at the base, below all applications.
===Release engineering===


Given their use in bootstrapping the SGX platform chain of trust, the architectural enclaves would normally be considered to be serving the same role as platform firmware would. They establish an association with the physical platform hardware, which all other SGX uses relies upon.
N/A - does not impact deliverables for releng


Application enclaves, meanwhile are clearly just userspace code, with a special protected execution context. They are created by ordinary application developers as needed to handle some specialized application tasks and have no relationship to platform firmware.
===Policies and guidelines===
 
==== Enclave execution context ====
 
All enclaves run in ''ring 3'', which is traditionally the realm of userspace. The execution context, while using a region of memory allocated by & accounted to the loading application, is securely isolated from everything else on the system including the loading application. The enclaves' roles can look like either firmware, or kernel or userspace roles depending on the context on what the enclave is doing.
 
Running in ''ring 3'' limits their ability to run privileged instructions, but the normal rules of access for rings do not apply. Nothing in ''ring 0''  ('''firmware''' / '''kernel'''), ''ring 3'' ('''userspace'''), or even ''psuedo-ring -1'' ('''SMM''') can interact with the enclaves, except via their published API entrypoints which are called via the EENTER instructions using a separate stack. IOW, the traditional view of hardware execution contexts being a simple stack of rings has been rather distorted by the capabilities of SGX, which exist as a distinct context off to the side of the rings model.
 
 
==== The architectural enclaves ====
 
There are 8 so called "architectural enclaves" built, signed and distributed by Intel.
 
* '''libsgx_le.signed.so''' - "Launch Enclave (le)"
** This was historically used to control what enclaves are able to be launched on a platform. Modern systems allow loading on any enclave no matter who signed it.
** This enclave '''requires''' an Intel signature
** ''This architectural enclave is considered obsolete & is NOT intended to be shipped in Fedora.''
 
* '''libsgx_qe.signed.so''' - "Quoting Enclave (qe)"
** This was historically used in attestation of enclaves, using the Enhanced Privacy ID (EPID) scheme, which is replaced by RSA in SGX DCAP (Data Center Attestation Primitives) software.
** This enclave '''requires''' an Intel signature
** ''This architectural enclave is considered obsolete & is NOT intended to be shipped in Fedora.''
 
* '''libsgx_pve.signed.so''' - "ProVisioning Enclave (pve)"
** This was also historically used in attestation of enclaves, using the Enhanced Privacy ID (EPID) scheme, which is replaced by RSA in SGX DCAP (Data Center Attestation Primitives) software.
** This enclave '''requires''' an Intel signature
** ''This architectural enclave is considered obsolete & is NOT intended to be shipped in Fedora.''
 
* '''libsgx_pce.signed.so''' - "Platform Certification Enclave (pce)"
** This certifies all other enclaves running on the system. The identity of the Intel's signing key, together with secrets inside the CPU set in fuses at time of manufacture, to derive a key that is known only to the enclave and Intel. This is needed in order to obtain a certificate from Intel that proves the hardware is genuine.
** This enclave '''requires''' an Intel signature
 
* '''libsgx_id_enclave.signed.so''' - "Identification Enclave (ide)"
** This is used to extract some identification information about the processor that is needed to acquire a platform /processor certificate after deploying or re-provisioning a platform.
** This enclave '''recommends''' an Intel signature
 
* '''libsgx_qe3.signed.so''' - "Quoting Enclave (qe3)"
** This is used in attestation of enclaves, using the newer RSA scheme in SGX DCAP
** This enclave '''recommends''' an Intel signature
 
* '''libsgx_tdqe3.signed.so''' - "Trust Domain Quoting Enclave (tdqe)"
** This is used in attestation of TDX virtual machines, using the newer RSA scheme in SGX DCAP
** This enclave '''recommends''' an Intel signature
 
* '''libsgx_qve.signed.so''' - "Quote Verification Enclave (qve)"
** This is used to provide a way to verify attestation reports on an otherwise untrusted machine using SGX DCAP.
** This enclave '''recommends''' an Intel signature
** The pre-built binary for this enclave includes a build of openssl that potentially contains forbidden crypto & is NOT intended to be shipped in Fedora unless the crypto can be approved or eliminated
 
Out of the four architectural enclaves that '''require''' an Intel signature, only one is intended to be shipped in Fedora.
 
While the remaining four architectural enclaves can theoretically have a non-Intel signature, if this is done it will increase friction of usage. The identity of the signer of enclaves becomes embedded in quotes, and is checked by the user (or software) validating the quote which is unlikely to be expecting a non-Intel signer for these architectural enclaves.
 
Thus it is considered that all shipped architectural enclaves need to have the Intel signature.
 
Users who wish to change & rebuild architectural enclaves from source can sign the result with their own keys, for all except the '''libsgx_pce.signed.so''' which unavoidably requires an Intel signature in order to derive the correct shared keys. If doing this, they will have to ensure that applications they use for verification are able to support use of non-Intel signers.
 
==== The firmware exception ====
 
The Fedora licensing guidelines describe the requirements for a pre-built binary to quality for the [https://docs.fedoraproject.org/en-US/legal/license-approval/#_licenses_allowed_for_firmware firmware exception] allowing source to be omitted.
 
* ''The files must be non-executable within the Fedora Linux context (note: this means that the files cannot run on their own, not that they are just chmod -x)''.
** ✅ Enclaves are distributed as ELF executable files, which must be loaded using specialized SGX supporting code that sets up the enclave execution context on the processor, not the regular platform ''ld-linux.so''.
 
* ''The files must not be libraries, within the Fedora Linux context''.
** ✅ While the enclaves '''.so''' file extension sugggests they are libraries, this is just a naming convention. The platform '''ld''' tool cannot link a binary to an enclave '''.so''' file, in the way a platform library is consumed. They must be loaded using specialized SGX supporting code that sets up the enclave execution context on the processor.
 
* ''The files must be standalone, not embedded in executable or library code (within the Fedora Linux context)''
** ✅ Every enclave is distributed as a standalone file, fully separated from any executable or library which may leverage its functionality.
 
* ''The files must be necessary for the functionality of open source code being included in Fedora Linux or to enable Fedora Linux to boot on a specific device, where no other reliable and supported mechanisms exist''
** ✅/❌ Depends on context of the enclave
 
Of the 4 pre-built, Intel signed, architectural proposed to be shipped, ''pce'' should trivially qualify. Without that there is no practical way to use SGX technology in Fedora, as no host certificate can be acquired to prove the hardware is genuine.
 
Of the remaining enclaves 'ide', 'qe3', 'tdqe', it is reasonable to say they are necessary, as verification of quotes from application enclaves will be expected to chain back to signer identities published by Intel. The purpose of the quoting enclaves is to prove use of a genuine Intel platform, and so the trust relationship for these enclaves is expected between the user and Intel to bootstrap use of the platform.


With application enclaves, there is goal is for the party who verifies the enclave output, to be able to demonstrate that known good code is executing in a secure context on Intel SGX. The verifying party needs to trust whomever built and signed the enclaves.  
A decision is needed around the handling of the pre-built, signed SGX enclaves. There are some relevant parallels in the guidelines for firmware as well as current practice wrt shim and CPU microcode.


Looking back at the description of "benefitting parties", if the signer of application enclaves can not be Fedora, then it is highly unlikely that SGX is being used in a way that benefits the Fedora user. With this in mind application enclaves should not ordinarily qualify under the 4th clause for the firmware exception.
Normal Fedora practice requires building everything from source. There is a general exception to this for firmware blobs, which don't need to be built from source and don't need to be under an OSS compliant license as long as the binaries can be freely distributed. Hardware firmware binaries almost always include a digital signature from the vendor, to ensure that only trusted firmware is loaded onto the device. Thus even if source code is available for a given firmware binary, Fedora would still need to be shipping it as a pre-built vendor supplied signed binary.


See the [https://fedoraproject.org/wiki/Changes/IntelSGX#Policies_and_guidelines Policies & guidelines] section for the concrete recommendation of how to apply Fedora policies.
Another example of shipping pre-built vendor binaries would be CPU microcode. This could be considered firmware for the core CPU, and again are vendor supplied, signed binaries, with no source code available.


== Feedback ==
A slightly different reference point is in the handling of ''shim'', where Fedora builds a binary from known good source, possibly with local pathes, and sends it off for signing by Microsoft, packaging the binary that is sent back. Microsoft has various requirements before it will permit signing a vendor's shim.


Consider if Fedora built a pristine shim release, with a designated toolchain version, using a reproducible build process. There would be no need to send the binary to Microsoft for signing, as the binary built in Fedora would match a standard pre-published signed binary from that shim release + toolchain. This is the situation SGX architectural enclaves are in. The main difference between the shim & SGX scenarios is that Fedora has the ability to add arbitrary local patches to shim & build with arbitrary toolchain versions of its choosing. This would not be possible when following a vendor specified reproducible build process.


== Benefit to Fedora ==
In the shim case, it is often (but not always) possible for users to enroll their own certificates in UEFI to bless shim signatures from vendors other than Microsoft. IOW, a user often has the ability to build & customize shim themselves signing with their own keys. In the case of SGX enclaves, this is possible for 7, out of the 8 architectural enclaves, however the most fundamental enclave (''pce'') must always have an Intel signature to bootstrap the hardware root of trust.
As a general purpose infrastructure technology, SGX can be applied to / used by a wide variety of scenarios / applications.


The primary goal in introducing SGX into Fedora, however, is to support the Fedora KVM virtualization stack when it introduces confidential virtual machines running with Intel TDX. The TDX attestation implementation in currently integrated with Intel CPUs is built on the SGX technology. Attestation is the means by which a guest VM owner, can prove that their VM machine is running in confidential mode on genuine Intel hardware, as opposed to being in "blue pill" environment.
'''In summary''', the architectural enclaves meet the definition of firmware documented in the Fedora licensing guidelines:


== Scope ==
* https://docs.fedoraproject.org/en-US/legal/license-approval/#_technical_firmware_requirements
=== Proposal owners===


Add the following packages to Fedora
Thus it should be permissible to ship the pre-built, signed binaries with no policy changes.


* '''CppMicroServices''' - a C++ runtime library for building microservices daemons
The shim model also gives impetus to the idea of it being acceptable to ship pre-built binaries, '''provided''' a reproducible build process can prove the binaries match the source under Fedora approved licenses.
* '''sgx-srpm-macros''' - define some common macros for where SGX content will live in the filesystem tree
* '''sgx-compat-gccXXX''' - one (or more) '''specific''' GCC versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-binutilsXXX''' - one (or more) '''specific''' binutils versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-nasmXXX''' - one (or more) '''specific''' NASM versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-glibc-headersXXX''' - one (or more) '''specific''' GCC versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''sgx-compat-kernel-headersXXX''' - one (or more) '''specific''' GCC versions, built with ''targetted configure arguments'', to match the GCC configuration required for enclave reproducible build.
* '''linux-sgx-enclavesXXX''' - one (or more) packages for performing a reproducible build of architectural enclaves
* '''linux-sgx''' - provide the SGX platform development headers & libraries, runtime libraries, and supporting daemons


The pre-built, signed architectural enclaves are not always re-created on each SGX release. New binaries are only issued if there was a required feature change, or a security fix required. Thus the package for the reproducible enclave builds is separated out from the general SGX package. Furthermore, to perform a reproducible build of the full set of enclaves, requires potentially more than one '''linux-sgx-enclavesXXX''' package. For example SGX 2.23 and 2.24 releases only updated the ''''qve'''' enclave, all other enclaves remained on version 2.22. This in turn creates the requirement for multiple '''GCC'''/'''binutils'''/'''nasm''' versions, at some points.  The current newest 2.25 release has updated all enclaves, so initially only a single ''''linux-sgx-enclaves-2_25'''' is expected to be required.


NB, [https://github.com/intel/linux-sgx/issues/1045 an upstream bug] has resulted in different parts of the enclave code being built with different GCC/binutils versions. This should be resolved in future releases:
Ultimately it is suggested to consider a hybrid between the two views. Treat the SGX enclaves as firmware, but none the less require a reproducible build process, to prove the binaries correspond to the claim OSS code.


NB, The requirement for glibc and kernel header packages is [https://github.com/intel/linux-sgx/pull/1062 likely another upstream bug]. The enclave code should be build exclusively against the SGX runtime, which is a completely custom C library. This is being investigated upstream.
It is further suggested that this not be limited to SGX enclaves, instead expand the existing firmware exception guidance, to require a reproducible build is performed if the pre-built signed firmware binaries have complete & corresponding soruce available with a supported reproducible build process.


=== Other developers===
The intent is to prove that the signed vendor firmware actually matches the published code whenever practical. This would apply to all SGX architectural enclaves, but also potentially to other distributed firmware with available source.
 
The kernel functionality required for SGX is already present in Fedora kernel packages, so no work by other maintainers is anticipated.
 
===Release engineering===
 
N/A - does not impact deliverables for releng
 
===Policies and guidelines===
 
* '''Architectural enclaves'''.
** Prebuilt binaries signed by Intel to be permitted under the existing firmware exception
** Given the availability of complete corresponding source code & a supported reproducible build process, all pre-built binaries MUST be verified through a reproducible build performed in Fedora, using a fully open source toolchain.
 
* '''Application enclaves'''
** No shipping of pre-built binaries permitted. Everything must follow normal Fedora policies requiring build from source. Any signature must use Fedora controlled persistent keys, or single use keys.
 
The distinction between architectural enclaves (signed by Intel to bootstrap trust) and application enclaves (signed by Fedora, with trust chained from the AEs), is considered conceptually similar to the distinction between shim (signed by Microsoft to bootstrap trust), vs kernel (signed by Fedora, with trust chained from shim).


===Trademark approval===
===Trademark approval===
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Do you require 'QA Blueprint' support? N
Do you require 'QA Blueprint' support? N


The proposed new packages are available for testing via Copr:
The proposed new packages are available for testing via Copr, until such time as they are reviewed & built in Fedora koji:


  https://copr.fedorainfracloud.org/coprs/berrange/sgx-ng/
* https://copr.fedorainfracloud.org/coprs/berrange/sgx-ng/
 
These should work on any Intel Xeon class platform


== How To Test ==
== How To Test ==
Line 273: Line 182:


At a later time, when support for Intel TDX is integrated into KVM and QEMU, the immediate Fedora user benefit will significantly expand.
At a later time, when support for Intel TDX is integrated into KVM and QEMU, the immediate Fedora user benefit will significantly expand.
=== Limitations ===
As noted earlier, due to the need for Intel signatures on 4 pre-built architectural enclaves there is a small constraint on user software freedom, if they choose to make use of SGX technology.
For the '''ide''', '''qe3''' and '''tdqe''' architectural enclaves, it is possible for users to rebuild the source with arbitrary local modifications, and sign the result with their own local key. The resulting enclaves can be deployed and used at runtime, however, it is not guaranteed that applications will be able to successfully verify quotes produced by such enclaves. It depends on whether applications have been written to expect non-Intel signatures.
For the '''pce'' architectural enclaves, it is possible for users to rebuild the source with arbitrary local modifications, and sign the result with their key. The resulting enclave can be deployed and used at runtime, however, it will not be possible to obtain a certificate from Intel proving authenticity of the hardware. Thus when verifying quotes, it will not be able to successfully verify the complete chain of trust.
There are no limitations on customization, rebuilds & re-signing of permitted application enclaves, as any usage with signing constraints is proposed to make such enclaves ineligible for inclusion in Fedora.


== Dependencies ==
== Dependencies ==


No existing packages will have a dependency on this change initially. In future, some deployments of QEMU may change to pull in certain SGX packages, to support Intel TDX.
The primary functional dependency for use of SGX is kernel support, which has existed in Fedora for some time. See "CONFIG_X86_SGX=y" in the kconfig files.
 
Kernel support for SGX already exists in Fedora:


  $ git grep CONFIG_X86_SGX=y
This change proposal does not rely on work by another other package maintainers, but new packages will require reviewer attention.
  kernel-x86_64-debug-fedora.config:CONFIG_X86_SGX=y
  kernel-x86_64-debug-rhel.config:CONFIG_X86_SGX=y
  kernel-x86_64-fedora.config:CONFIG_X86_SGX=y
  kernel-x86_64-rhel.config:CONFIG_X86_SGX=y
  kernel-x86_64-rt-debug-rhel.config:CONFIG_X86_SGX=y
  kernel-x86_64-rt-rhel.config:CONFIG_X86_SGX=y


== Contingency Plan ==
== Contingency Plan ==


<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
* Contingency mechanism: (What to do?  Who will do it?) N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
* Contingency deadline: N/A (not a System Wide Change)  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
* Blocks release? N/A (not a System Wide Change), Yes/No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->


* Contingency mechanism: The new packages have no ill effects on existing Fedora usage. Any outstanding work can be postponed to a later release if required.
* Contingency deadline: Beta free
* Blocks release? No


== Documentation ==
== Documentation ==
<!-- Is there upstream documentation on this change, or notes you have written yourself?  Link to that material here so other interested developers can get involved. -->


<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
Documentation will be provided to describe:
N/A (not a System Wide Change)
 
* Configuring hardware UEFI to enable use of SGX
* Obtaining PCK certificates for a host from the Intel trusted services API
 
A subsequent change proposal will cover usage of SGX with TDX confidential virtual machines.


== Release Notes ==
== Release Notes ==

Latest revision as of 16:12, 25 October 2024

Intel SGX Software Stack

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.

Summary

The Intel SGX technology enables creation of execution enclaves, whose memory is encrypted and thus protected from all other code running on the machine, including SMM, firmware, kernel and userspace. This proposal is to introduce the SGX host software stack to Fedora, to enable applications and features which have a dependency on SGX technology.

Owner

Current status

  • Targeted release: Fedora Linux 42
  • Last updated: 2024-10-25
  • [Announced]
  • [<will be assigned by the Wrangler> Discussion thread]
  • FESCo issue: <will be assigned by the Wrangler>
  • Tracker bug: <will be assigned by the Wrangler>
  • Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

The Intel SGX technology enables creation of execution enclaves, whose memory is encrypted and thus protected from all other code running on the machine, including SMM, firmware, kernel and userspace. While it has many potential use cases, this proposal is focused around the infrastructure needed to enable support for attestation of TDX confidential virtual machines.

The SGX software stack compromises a number of components

  • Support for developing new enclaves
    • Header files for the enclave code (a minimalist C library, C++ library, crypto and some other misc libraries)
    • Static library archives for the enclave code.
    • Build helper tools (for signing enclaves, generating code enclave API entrypoints)
  • Support for developing applications that use enclaves
    • Header files for platform code
    • Dynamic libraries for platform code
  • Support for deploying applications that use enclaves
    • Enclave service daemon - assists unprivileged applications in loading enclaves
    • Registration tools - assists platform administrator in acquiring certificates to identity the platform
    • Quote generation daemon - assists QEMU in acquiring signed attestation reports for TDX VMs.

The code and binaries related to the host OS platform components will be installed in the normal filesystem locations common to all Fedora packages.

For the purposes of packaging, the enclaves will be treated as cross-compilation target. While the build architecture is x86_64, the runtime has custom C / C++ libraries that must be used, and separate code loader.

With this in mind, all enclave related code and binaries are proposed to be installed at /usr/x86_64-intel-sgx, specifically under lib64 and include sub-directories.

The generated binary packages will generally all have an 'sgx-' prefix to their name, with enclave related packages having an more specialized 'sgx-enclave-' name prefix.

Feedback

Benefit to Fedora

As a general purpose infrastructure technology, SGX can be applied to / used by a wide variety of scenarios / applications.

The primary goal in introducing SGX into Fedora, however, is to support the Fedora KVM virtualization stack when it introduces confidential virtual machines running with Intel TDX. The TDX attestation implementation in currently integrated with Intel CPUs is built on the SGX technology. Attestation is the means by which a guest VM owner, can prove that their VM machine is running in confidential mode on genuine Intel hardware, as opposed to being in "blue pill" environment.

Scope

Proposal owners

Add at least the following source packages to Fedora:

  • CppMicroServices - a C++ runtime library for building microservices daemons
  • sgx-srpm-macros - define some common macros for where SGX content will live in the filesystem tree
  • linux-sgx - provide the SGX platform development headers & libraries, runtime libraries, and supporting daemons

Assuming that pre-built, signed SGX architectural enclaves will be shipped, the following additional package is proposed:

  • linux-sgx-enclavesXXX - one (or more) packages containing architectural enclaves

Not every architectural enclave binary is re-issued on every release. New signed builds are only made available when there is a CVE fix, or a feature enhancement. At time of writing the SGX 2.25 release included new builds for every enclave. A future 2.26 release may only update a subset. Hence at some points in time, Fedora may have more than one linux-sgx-encalvesXXX package present.

If it is required to perform a reproducible build of the above architectural enclave binaries, to prove the binaries match the claimed sources, the following toolchain packages are needed:

  • sgx-compat-gccXXX - one (or more) specific GCC versions, built with targetted configure arguments, to match the GCC configuration required for enclave reproducible build.
  • sgx-compat-binutilsXXX - one (or more) specific binutils versions, built with targetted configure arguments, to match the GCC configuration required for enclave reproducible build.
  • sgx-compat-nasmXXX - one (or more) specific NASM versions, built with targetted configure arguments, to match the GCC configuration required for enclave reproducible build.
  • sgx-compat-glibc-headersXXX - one (or more) specific GCC versions, built with targetted configure arguments, to match the GCC configuration required for enclave reproducible build.
  • sgx-compat-kernel-headersXXX - one (or more) specific GCC versions, built with targetted configure arguments, to match the GCC configuration required for enclave reproducible build.

At time of writing, with the SGX 2.25 release, the versions required to perform a fully reproducible build will be

  • gcc: 8.5.0, 9.5.0
  • binutils: 2.38, 2.40
  • nasm: 2.16.01
  • glibc: 2.38
  • kernel: 5.17

Note, while Fedora already ships builds fo gcc, binutils, etc, performing reproducible builds requires specific versions, configured with particular choice of build options. Hence the intention to ship parallel packages, which are exclusively intended for use in reproducing enclaves. There will be no support for using these toolchain packages for any other situation in Fedora.

Note: the fact that two versions are needed for binutils and GCC, is an upstream an upstream bug

Note: the enclaves are supposed to be built exclusively against the SGX SDK which provides its own C runtime headers. Thus the fact that it has a requirement for header files from glibc & kernel is also likely another upstream bug.

The full set of proposed source RPMs and their corresponding binary RPM outputs can be see from Copr:

https://copr.fedorainfracloud.org/coprs/berrange/sgx-ng/monitor/

Note, the pre-built, signed architectural enclaves are not always re-created on each SGX release.

Other developers

It is not anticipated that other package maintainers need do anything to support introduction of SGX. The kernel is already built with the SGX feature enabled.

systemd ships with udev rules to enable creation of some of the required device nodes. The SGX package contains addon udev rules for remaining device nodes. The latter may be contributed upstream to systemd in future, and would flow back into Fedora in a normal systemd update.

Release engineering

N/A - does not impact deliverables for releng

Policies and guidelines

A decision is needed around the handling of the pre-built, signed SGX enclaves. There are some relevant parallels in the guidelines for firmware as well as current practice wrt shim and CPU microcode.

Normal Fedora practice requires building everything from source. There is a general exception to this for firmware blobs, which don't need to be built from source and don't need to be under an OSS compliant license as long as the binaries can be freely distributed. Hardware firmware binaries almost always include a digital signature from the vendor, to ensure that only trusted firmware is loaded onto the device. Thus even if source code is available for a given firmware binary, Fedora would still need to be shipping it as a pre-built vendor supplied signed binary.

Another example of shipping pre-built vendor binaries would be CPU microcode. This could be considered firmware for the core CPU, and again are vendor supplied, signed binaries, with no source code available.

A slightly different reference point is in the handling of shim, where Fedora builds a binary from known good source, possibly with local pathes, and sends it off for signing by Microsoft, packaging the binary that is sent back. Microsoft has various requirements before it will permit signing a vendor's shim.

Consider if Fedora built a pristine shim release, with a designated toolchain version, using a reproducible build process. There would be no need to send the binary to Microsoft for signing, as the binary built in Fedora would match a standard pre-published signed binary from that shim release + toolchain. This is the situation SGX architectural enclaves are in. The main difference between the shim & SGX scenarios is that Fedora has the ability to add arbitrary local patches to shim & build with arbitrary toolchain versions of its choosing. This would not be possible when following a vendor specified reproducible build process.

In the shim case, it is often (but not always) possible for users to enroll their own certificates in UEFI to bless shim signatures from vendors other than Microsoft. IOW, a user often has the ability to build & customize shim themselves signing with their own keys. In the case of SGX enclaves, this is possible for 7, out of the 8 architectural enclaves, however the most fundamental enclave (pce) must always have an Intel signature to bootstrap the hardware root of trust.

In summary, the architectural enclaves meet the definition of firmware documented in the Fedora licensing guidelines:

Thus it should be permissible to ship the pre-built, signed binaries with no policy changes.

The shim model also gives impetus to the idea of it being acceptable to ship pre-built binaries, provided a reproducible build process can prove the binaries match the source under Fedora approved licenses.


Ultimately it is suggested to consider a hybrid between the two views. Treat the SGX enclaves as firmware, but none the less require a reproducible build process, to prove the binaries correspond to the claim OSS code.

It is further suggested that this not be limited to SGX enclaves, instead expand the existing firmware exception guidance, to require a reproducible build is performed if the pre-built signed firmware binaries have complete & corresponding soruce available with a supported reproducible build process.

The intent is to prove that the signed vendor firmware actually matches the published code whenever practical. This would apply to all SGX architectural enclaves, but also potentially to other distributed firmware with available source.

Trademark approval

N/A

Alignment with the Fedora Strategy

This aligns with

  • "Reaching the world". Including SGX will make the Fedora support for hosting Intel TDX confidential virtual machines feature complete, by enabling attestation by the guest owner
  • "Innovation & leadership in technology". SGX is a general purpose infrastructure technology which enables application developers to build systems to securely run sensitive workloads.

Upgrade/compatibility impact

This is a new package set which should not have any upgrade impact, as it will not initially be a dependency of other software. In future it may be pulled in automatically as a dependency in certain KVM deployment scenarios. Even when installed, using anything related to SGX first requires host firmware changes to enable use of the technology. The systemd services provided have their unit files conditionalized on the existence of /dev/sgx_enclave device nodes.

Early Testing (Optional)

Do you require 'QA Blueprint' support? N

The proposed new packages are available for testing via Copr, until such time as they are reviewed & built in Fedora koji:

These should work on any Intel Xeon class platform

How To Test

  • Document how to validate a single-socket system by obtaining PCK certificates automatically
  • Document how to configure a multi-socket system to enable its registration with Intel services, and request a PCK certificate

User Experience

Initially minimal user experience impact, since on its own it doesn't deliver noticeable end user features, as it is not believed that any existing applications in Fedora are able to leverage SGX.

The initial user benefit will be that users can bootstrap trust in SGX on their Fedora host. This will facilitate users in deploying 3rd party applications of their choosing that utilize SGX.

At a later time, when support for Intel TDX is integrated into KVM and QEMU, the immediate Fedora user benefit will significantly expand.

Dependencies

The primary functional dependency for use of SGX is kernel support, which has existed in Fedora for some time. See "CONFIG_X86_SGX=y" in the kconfig files.

This change proposal does not rely on work by another other package maintainers, but new packages will require reviewer attention.

Contingency Plan

  • Contingency mechanism: The new packages have no ill effects on existing Fedora usage. Any outstanding work can be postponed to a later release if required.
  • Contingency deadline: Beta free
  • Blocks release? No

Documentation

Documentation will be provided to describe:

  • Configuring hardware UEFI to enable use of SGX
  • Obtaining PCK certificates for a host from the Intel trusted services API

A subsequent change proposal will cover usage of SGX with TDX confidential virtual machines.

Release Notes

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