The 2017 Linux Security Summit
18 Sep 2017 tags: android apparmor ima seccomp selinux smackThe past Thursday and Friday was the 2017 Linux Security Summit, and once again I think it was a great success. A round of thanks to James Morris for leading the effort, the program committee for selecting a solid set of talks (we saw a big increase in submissions this year), the presenters, the attendees, the Linux Foundation, and our sponsor - thank you all!
Unfortunately we don’t have recordings of the talks, but I’ve included my notes on each of the presentations below. I’ve also included links to the slides, but not all of the slides were available at the time of writing; check the LSS 2017 slide archive for updates.
ARMv8.3 Pointer Authentication - Mark Rutland, ARM Ltd.
Traditional memory protection mechanisms have focused on preventing code injection, success in this area has refocused attacks on reusing existing code, e.g. ROP attacks. While code reuse mitigations do exist, they are not widely deployed due to difficulties in integration and impacts on performance and debugging. ARM’s pointer authentication is designed to help prevent against code reuse attacks while minimizing these negative impacts. The pointer authentication works by combining a pointer value, 64-bit context, and 128-bit private key into a Pointer Authentication Code (PAC) which is inserted into a reserved portion of the pointer (a pointer with a 48-bit VA space has a 7-bit PAC); the pointer value can later be authenticated before it is dereferenced. Linux Kernel patches have been posted to enable userspace protection with per-process PAC keys. Compiler support is already present in GCC v7 using the “-msign-return-address” option, although GDB support is currently blocked on the acceptance of the kernel ptrace patches.
Defeating Invisible Enemies: Firmware Based Security in the OpenPOWER Platform - George Wilson, IBM
The past few years have proven firmware based threats to be a real problem, with the various secure and trusted boot solutions providing an method to help eliminate these risks. The OpenPOWER Foundation has been working to map the Trusted Computing Group’s secure boot specifications to the OpenPOWER platform as well as provide a freely available working secure boot implementation for the platform.
Landlock LSM: Towards Unprivileged Sandboxing - Mickael Salaun
Multiple application sandboxing mechanisms exist today, Landlock attempts to do better than most by providing fine-grained access control with embedded policy to any application on the system, including unprivileged applications. The Landlock LSM does this by allowing applications to write their own sandbox policy using eBPF. While this may sound similar to the existing seccomp-bpf based approaches, Landlock provides mechanisms to incorporate object information into the sandbox policy; something that is not possible with the existing seccomp-bpf mechanism. Landlock remains a work in progress, but v7 is considered to be a minimally viable product and has been posted upstream for review.
The State of Kernel Self-Protection - Kees Cook, Google
The Kernel Self Protection Project (KSPP) provided a quick introduction on the motivation and goals for the project before moving on to an overview of some of the bug classes they are working on eliminating in the Linux Kernel, and concluded with a discussion of some of the challenges facing the project and the broader kernel community. While progress can be slow, it was encouraging to see that ~12 organizations and ~10 unaffiliated individuals have joined the KSPP effort and are currently working on ~20 features.
Confessions of a Security Hardware Driver Maintainer - Gilad Ben-Yossef, ARM Ltd.
The presentation started with an overview of the Android secure boot process before introducing the ARM Trustzone CryptoCell, a security processor which appears similar to a TPM. The presenter went over some of the challenges he faced integrating the CryptoCell into the boot process, including some of the work that went into improving the performance of the solution.
CII Best Practices Badge, 1.5 Years Later - David Wheeler, IDA
The Linux Foundation’s Core Infrastructure Initiative’s (CII) Best Practices Badge Program has been running for approximately one and a half years; this talk provided a basic introduction, observations from the first 18 months, and some recent additions to the badge program. The CII Badge Program has approximately 1000 self-registered projects, with about 100 of those projects earning the “Best Practices” badge. Interestingly, this 10% success rate seems to be holding true, even as the number of total projects grow. The higher level Silver and Gold badges, recent additions to the program, were also discussed.
The Smack 10th Year Update - Casey Schaufler
This year marks Smack’s 10th anniversary, and sees Smack continuing to be part of Tizen and Automotive Grade Linux. Despite the anniversary, the past year was a relatively quiet one for Smack with only one new feature: marking signal delivery as an “append” and not a “write” operation.
Integrity Subsystem Update - Mimi Zohar, IBM
The Integrity subsystem update started with a summary of the subsystem’s functionality before presenting some of the recent additions and ongoing efforts. Recent additions include the ability to pass the IMA measurements across the kexec boundary, deeper embedding into the VFS layer, and support for “appended signatures”. The appended signature feature is initially being used to verify loadable kernel modules, but it could be used for any number of objects that are passed into the kernel as memory buffers and not files. Future work includes performance improvements, namespacing, and UEFI support.
TPM Subsystem Update - Jarkko Sakkinen, Intel Corporation
The Trusted Platform Module (TPM) subsystem update started with an introduction to the subsystem and a history of the TPM before presenting the new work from the past year. New functionality included the addition of a TPM v2.0 resource manager and event log, as well as 64-bit ARM support.
Thursday BoFs
As I was busy participating in both the “extreme” LSM stacking and LSM namespacing BoFs I wasn’t able to capture much in the way of notes.
Hatching Security: LinuxKit as Security Incubator - Tycho Andersen & Riyaz Faizullabhoy, Docker
LinuxKit was designed to make it easy for people to create their own Linux distribution, with a strong focus on minimal OS installs such as one would use in a container hosting environment. LinuxKit has several features that make it interesting from a security perspective, the most notable being the read-only rootfs which is managed using external tooling. Applications are installed via signed container images. In addition to software, LinuxKit also has a Special Interest Group (SIG) which meets bi-weekly and hosts a number of presentations related to Linux security and hardening.
This talk also spent some time talking about eXclusive Page Frame Ownership (XPFO). XPFO is a mechanism which protects against ret2dir (return to direct mapped memory) attacks; this is important as many of the existing ret2usr (return to userspace memory) mitigations are not successful against ret2dir. The XPFO work remains a work in progress.
Running Linux in a Shielded VM - Michael Kelley, Microsoft
Microsoft Shielded VMs are built on Hyper-V and designed to protect the VM data both at rest and in-flight. Shielded VMs block administrators from the VM data, provide a mechanism for attesting the hypervisor, and guard the hypervisor fabric from attacks. This is accomplished by mixing a variety of technologies; one that is particularly interesting is the “synthetic TPM”. A synthetic TPM is a TPM that is exposed to the guest, but is not backed by a physical TPM as you would expect with a virtual TPM (vTPM). While the synthetic TPM (sTPM?) can not offer as strong of a security assurance as a physical, or even virtual TPM, it does offer the ability to migrate the TPM with the guest, a critical requirement for cloud providers wishing to provide a TPM to guests.
Keys Subsystem - David Howells, Red Hat
David Howells presented a quick update on the changes to the kernel keyring over the past year as well as current development efforts. Changes over the past year included protecting big keys by encrypting them with a transient key, restricted keyings, and support for Diffie-Hellman operations. Current efforts include notifications on keyring changes, use counters, decomposing the setattr operations, and keyring namespacing.
Protecting VM Register State with AMD SEV-ES, David Kaplan, AMD
The presentation started with a description of AMD’s Secure Encrypted Virtualization (SEV) and the AES cryptographic processor built into the memory controller. SEV-ES, is not just a palindrome (!), it is also a mechanism which expands SEV’s protection from memory pages to register state. Basic Secure Memory Encryption (SME) support is in the upstream Linux Kernel, with SEV patches posted to the lists. The associated OVMF/BIOS patches have already been accepted. Initial hardware support is shipping in AMD’s Ryzen Threadripper CPUs.
Proposal of a Method to Prevent Privilege Escalation Attacks for Linux Kernel - Yuichi Nakamura, Hitachi Ltd. & Toshihiro Yamauchi, Okayama University
Unfortunately I missed the start of this presentation, but the goal of this proposal is the detection and prevention of privilege escalation by detecting unexpected credential changes during syscall execution in the kernel. The talk included measurements documenting the minimal performance impact and demos showing how this technology would help mitigate a number of published CVEs. Unfortunately additional work is still needed to protect against smart exploits tricking the new proposed checks.
SELinux in Android O: Separating Policy to Allow for Independent Updates - Daniel Cashman, Google
Android v8.0, aka “Oreo”, is the latest Android release and it includes a number of SELinux related changes. The most significant of these changes is project Treble, which is a redesign of the Android SELinux policy to enable updating of the general Android code independent of the hardware specific code. The presentation discussed the approach taken with the SELinux policy rework, including the advantages, disadvantages, and various lessons learned during development.
SELinux Subsystem Update - Paul Moore, Red Hat
I delivered the annual “State of SELinux” presentation, slides are available below.
AppArmor Subsystem Update - John Johansen, Canonical Group, Ltd.
AppArmor has historically carried a rather large patchset in Ubuntu, but over the past year the AppArmor developers have started working on upstreaming this code; this is still a work in progress, but most of the changes have made their way into Linus’ tree. The current AppArmor approach to namespacing was also discussed.
Seccomp Subsystem Update - Kees Cook, Google
The seccomp subsystem update started with an introduction to seccomp, and moved to the new features added to kernel subsystem over the past year. Significant changes include the generation of coredumps when a process is killed, a new action to support killing the entire process and not just the offending thread, logging improvements, and better regression testing.
Securing Automated Decryption - Nathaniel McCallum, Red Hat
This presentation described some of the challenges to using typical key escrow models in large scale-out deployments and presented a novel new solution to provide an automated way to securely manage keys across a large number of systems. The technology is based on a Diffie-Hellman algorithm variant, McCallum-Relyea, which is implemented in a client (Clevis) and server (Tang). While the Linux Security Summit presentations were not recorded this year, Nathaniel did give a very similar talk at DevConf.cz 2017, which was recorded, the link can be found below.