AWS re:Invent 2019: Speculation & leakage: Timing side channels & multi-tenant computing
> In January 2018, the world learned about Spectre and Meltdown, a new class of issues that affects virtually all modern CPUs via nearly imperceptible changes to their micro-architectural states and can result in full access to physical RAM or leaking of state between threads, processes, or guests. In this session, we examine one of these side-channel attacks in detail and explore the implications for multi-tenant computing. We discuss AWS design decisions and what AWS does to protect your instances, containers, and function invocations. Finally, we discuss what the future looks like in the presence of this new class of issue.
This is a good recap. Specific defenses starts around 42:00.
Speculative Load Hardening
> While several approaches are being actively pursued to mitigate specific branches and/or loads inside especially risky software (most notably various OS kernels), these approaches require manual and/or static analysis aided auditing of code and explicit source changes to apply the mitigation. They are unlikely to scale well to large applications. We are proposing a comprehensive mitigation approach that would apply automatically across an entire program rather than through manual changes to the code. While this is likely to have a high performance cost, some applications may be in a good position to take this performance / security tradeoff.
OpenSSH Key Shielding
> On June 21, 2019, support for SSH key shielding was introduced into the OpenBSD tree, from which the OpenSSH releases are derived. SSH key shielding is a measure intended to protect private keys in RAM against attacks that abuse bugs in speculative execution that current CPUs exhibit. This functionality has been part of OpenSSH since the 8.1 release. SSH private keys are now being held in memory in a shielded form; keys are only unshielded when they are used and re‐shielded as soon as they are no longer in active use. When a key is shielded, it is encrypted in memory with AES‐256‐CTR; this is how it works:
> Pointer authentication is a technology which offers strong probabilistic protection against exploiting a broad class of memory bugs to take control of program execution. When adopted consistently in a language ABI, it provides a form of relatively fine-grained control flow integrity (CFI) check that resists both return-oriented programming (ROP) and jump-oriented programming (JOP) attacks.
> While pointer authentication can be implemented purely in software, direct hardware support (e.g. as provided by ARMv8.3) can dramatically lower the execution speed and code size costs. Similarly, while pointer authentication can be implemented on any architecture, taking advantage of the (typically) excess addressing range of a target with 64-bit pointers minimizes the impact on memory performance and can allow interoperation with existing code (by disabling pointer authentication dynamically). This document will generally attempt to present the pointer authentication feature independent of any hardware implementation or ABI. Considerations that are implementation-specific are clearly identified throughout.
Defense in depth against SSRF vulnerabilities with the EC2 Instance Metadata Service
> Today, AWS is making v2 of the EC2 Instance Metadata Service (IMDSv2) available. The existing instance metadata service (IMDSv1) is fully secure, and AWS will continue to support it. But IMDSv2 adds new “belt and suspenders” protections for four types of vulnerabilities that could be used to try to access the IMDS. These new protections go well beyond other types of mitigations, while working seamlessly with existing mitigations such as restricting IAM roles and using local firewall rules to restrict access to the IMDS. AWS is also making new versions of the AWS SDKs and CLIs available that support IMDSv2.
Eh, seems this could have been better from the start, but oh well.
Some near-term arm64 hardening patches
> The arm64 architecture is found at the core of many, if not most, mobile devices; that means that arm64 devices are destined to be the target of attackers worldwide. That has led to a high level of interest in technologies that can harden these systems. There are currently several such technologies, based in both hardware and software, that are being readied for the arm64 kernel; read on for a survey on what is coming.
The Bytecode Alliance: Building a secure, composable future for WebAssembly
> We have a vision of a WebAssembly ecosystem that is secure by default, fixing cracks in today’s software foundations. And based on advances rapidly emerging in the WebAssembly community, we believe we can make this vision real.
> WebAssembly can provide the kind of isolation that makes it safe to run untrusted code. We can have an architecture that’s like Unix’s many small processes, or like containers and microservices. But this isolation is much lighter weight, and the communication between them isn’t much slower than a regular function call. This means you can use them to wrap a single WebAssembly module instance, or a small collection of module instances that want to share things like memory among themselves.
Two New Tools that Tame the Treachery of Files
> Parsing is hard, even when a file format is well specified. But when the specification is ambiguous, it leads to unintended and strange parser and interpreter behaviors that make file formats susceptible to security vulnerabilities. What if we could automatically generate a “safe” subset of any file format, along with an associated, verified parser? That’s our collective goal in Dr. Sergey Bratus’s DARPA SafeDocs program.
> We’ve developed two new tools that take the pain out of parsing and make file formats safer:
> PolyFile: A polyglot-aware file identification utility with manually instrumented parsers that can semantically label the bytes of a file hierarchically; and
> PolyTracker: An automated instrumentation framework that efficiently tracks input file taint through the execution of a program.
Defense at Scale
> Last year, my colleague Chris Rohlf gave a keynote at BSidesNOLA entitled “Offense at Scale”. Offense sounds fun. Pwn all the things. And you’re always going to win! And normally I’m a big fan of being massively offensive. Unfortunately, I find myself on the defense when it comes to information security.
> Here’s how you defend at scale. Can’t be done. The end. Everything’s fucked. You’re pwned.
Plenty of good points here. Also a fun read.
APRR - Access Protection ReRouting
> Almost a year ago I did a write-up on KTRR, first introduced in Apple’s A10 chip series. Now over the course of the last year, there has been a good bit of talk as well as confusion about the new mitigations shipped with Apple’s A12. One big change, PAC, has already been torn down in detail by Brandon Azad, so I’m gonna leave that out here. What’s left to cover is more than just APRR, but APRR is certainly the biggest chunk, hence the title of this post.
> APRR is a pretty cool feature, even if parts of it are kinda broke. What I really like about it (besides the fact that it is an efficient and elegant solution to switching privileges) is that it untangles EL1 and EL0 memory permissions, giving you more flexibility than a standard ARMv8 implementation. What I don’t like though is that it has clearly been designed as a lockdown feature, allowing you only to take permissions away rather than freely remap them.
> It’s also evident that Apple is really fond of post-exploit mitigations, or just mitigations in general. And on one hand, getting control over the physical address space is a good bit harder now. But on the other hand, Apple’s stacking of mitigations is taking a problematic turn when adding new mitigations actively creates vulnerabilities now.
Adopting the Arm Memory Tagging Extension in Android
> As part of our continuous commitment to improve the security of the Android ecosystem, we are partnering with Arm to design the memory tagging extension (MTE). Memory safety bugs, common in C and C++, remain one of the largest vulnerabilities in the Android platform and although there have been previous hardening efforts, memory safety bugs comprised more than half of the high priority security bugs in Android 9.
> We believe that memory tagging will detect the most common classes of memory safety bugs in the wild, helping vendors identify and fix them, discouraging malicious actors from exploiting them. During the past year, our team has been working to ensure readiness of the Android platform and application software for MTE. We have deployed HWASAN, a software implementation of the memory tagging concept, to test our entire platform and a few select apps. This deployment has uncovered close to 100 memory safety bugs. The majority of these bugs were detected on HWASAN enabled phones in everyday use. MTE will greatly improve upon this in terms of overhead, ease of deployment, and scale. In parallel, we have been working on supporting MTE in the LLVM compiler toolchain and in the Linux kernel. The Android platform support for MTE will be complete by the time of silicon availability.
Map Guard and Intel MPK
> Earlier this year I pushed a small library to Github called Map Guard. The goal of Map Guard is to enforce non-invasive security policies with regards to how pages of memory may be allocated, or modified, with the mmap syscall. For example, we may want to deny any page allocations marked Read, Write, and Execute as it introduces an easy mechanism for an exploit developer to take advantage of. In the rest of this post I will break down the approach I took to implement each of these security policies, and finally how Map Guard uses Intel’s Memory Protection Keys to allow transparently enabling Execute Only memory for all regions of mapped code.
security things in Linux v5.2
> page allocator freelist randomization
And some other things as well.
security things in Linux v5.1
> Linux kernel v5.1 has been released! Here are some security-related things that stood out to me:
Assessing Unikernel Security
> Unikernels are small, specialized, single-address-space machine images constructed by treating component applications and drivers like libraries and compiling them, along with a kernel and a thin OS layer, into a single binary blob. Proponents of unikernels claim that their smaller codebase and lack of excess services make them more efficient and secure than full-OS virtual machines and containers. We surveyed two major unikernels, Rumprun and IncludeOS, and found that this was decidedly not the case: unikernels, which in many ways resemble embedded systems, appear to have a similarly minimal level of security. Features like ASLR, W^X, stack canaries, heap integrity checks and more are either completely absent or seriously flawed. If an application running on such a system contains a memory corruption vulnerability, it is often possible for attackers to gain code execution, even in cases where the application’s source and binary are unknown. Furthermore, because the application and the kernel run together as a single process, an attacker who compromises a unikernel can immediately exploit functionality that would require privilege escalation on a regular OS, e.g. arbitrary packet I/O. We demonstrate such attacks on both Rumprun and IncludeOS unikernels, and recommend measures to mitigate them.
A year with Spectre: a V8 perspective
> In theory, it would be sufficient to defeat either of the two components of an attack. Since we do not know of any way to defeat any of the parts perfectly, we designed and deployed mitigations that greatly reduce the amount of information that is leaked into CPU caches and mitigations that make it hard to recover the hidden state.
> Fortunately or unfortunately, our offensive research advanced much faster than our defensive research, and we quickly discovered that software mitigation of all possible leaks due to Spectre was infeasible. This was due to a variety of reasons. First, the engineering effort diverted to combating Spectre was disproportionate to its threat level. In V8 we face many other security threats that are much worse, from direct out-of-bound reads due to regular bugs (faster and more direct than Spectre), out-of-bound writes (impossible with Spectre, and worse) and potential remote code execution (impossible with Spectre and much, much worse). Second, the increasingly complicated mitigations that we designed and implemented carried significant complexity, which is technical debt and might actually increase the attack surface, and performance overheads. Third, testing and maintaining mitigations for microarchitectural leaks is even trickier than designing gadgets themselves, since it’s hard to be sure the mitigations continue working as designed. At least once, important mitigations were effectively undone by later compiler optimizations. Fourth, we found that effective mitigation of some variants of Spectre, particularly variant 4, to be simply infeasible in software, even after a heroic effort by our partners at Apple to combat the problem in their JIT compiler.
Local privilege escalation via the Windows I/O Manager: a variant finding collaboration
> In Windows, when a system call is made from a user mode thread, the system call handler records this in the thread object by setting its PreviousMode field to UserMode. If instead the system call is made from kernel mode using a Zw-prefixed function, or from a system thread, the PreviousMode of the thread will be set to KernelMode. This method of distinguishing between user mode and kernel mode callers is used to help determine if the arguments of the call are from a trusted or untrusted source, and therefore to what extent they need to be validated by the kernel.
> In his research, James found that there were various kernel mode drivers shipped with Windows that, when handling IRP_MJ_CREATE requests, check the IRP’s RequestorMode, but do not check for SL_FORCE_ACCESS_CHECK. Furthermore, these are potentially exploitable via kernel mode code that, on the face of it, appears to be doing the correct thing in setting IO_FORCE_ACCESS_CHECK when creating or opening a file. An attacker obtaining sufficient control of the arguments of a file create/open call, via some request originating from user mode, could use this to send an IRP_MJ_CREATE request where the RequestorMode is KernelMode. If the RequestorMode check is used in a security decision, this may lead to a local privilege escalation vulnerability.
Chrome + Windows Exploit: Security Beyond Bugfixes
> There’s a publicly visible patch for the Chrome bug, however there aren’t a lot of details on the Windows kernel bug. The Google team states that they think it may be only possible to exploit this bug against Windows 7, and not newer Windows versions -- even if the bug does exist there. I want to use the remainder of this post to explain reasons that is -- based on the information we have.
> It’s very common to think about computer security primarily in terms of fixing vulnerabilities. In reality, security teams spend a lot of their time on a different goal: making bugs hard to exploit. This often takes the form of lowering privileges and introducing exploit mitigations. Windows 10 has a lot of investment in those areas, whereas Windows 7 doesn’t contain any of the improvements made in the last several years. That’s why even though Windows 7 continues to receive security bug fixes from Microsoft, it is considerably less safe to use.
Introducing Adiantum: Encryption for the Next Billion Users
> Where AES is used, the conventional solution for disk encryption is to use the XTS or CBC-ESSIV modes of operation, which are length-preserving. Currently Android supports AES-128-CBC-ESSIV for full-disk encryption and AES-256-XTS for file-based encryption. However, when AES performance is insufficient there is no widely accepted alternative that has sufficient performance on lower-end ARM processors.
> To solve this problem, we have designed a new encryption mode called Adiantum. Adiantum allows us to use the ChaCha stream cipher in a length-preserving mode, by adapting ideas from AES-based proposals for length-preserving encryption such as HCTR and HCH. On ARM Cortex-A7, Adiantum encryption and decryption on 4096-byte sectors is about 10.6 cycles per byte, around 5x faster than AES-256-XTS.
Paper link: https://tosc.iacr.org/index.php/ToSC/article/view/7360
Protecting your data, no matter where you go on the web
> We help keep your Google Account safe by proactively detecting and responding to security threats. For example, we already automatically reset the password on your Google Account if it may have been exposed in a third party data breach—a security measure that reduces the risk of your account getting hacked by a factor of ten.
> But we want to provide you with the same data breach protections for your accounts, beyond just Google apps and sites. This is where the new Password Checkup Chrome extension can help. If we detect that a username and password on a site you use is one of over 4 billion credentials that we know have been compromised, the extension will trigger an automatic warning and suggest that you change your password.