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Speculation Attack Against Intel’s SGX

Another speculative-execution attack against Intel’s SGX.

At a high level, SGX is a new feature in modern Intel CPUs which allows computers to protect users’ data even if the entire system falls under the attacker’s control. While it was previously believed that SGX is resilient to speculative execution attacks (such as Meltdown and Spectre), Foreshadow demonstrates how speculative execution can be exploited for reading the contents of SGX-protected memory as well as extracting the machine’s private attestation key. Making things worse, due to SGX’s privacy features, an attestation report cannot be linked to the identity of its signer. Thus, it only takes a single compromised SGX machine to erode trust in the entire SGX ecosystem.

News article.

The details of the Foreshadow attack are a little more complicated than those of Meltdown. In Meltdown, the attempt to perform an illegal read of kernel memory triggers the page fault mechanism (by which the processor and operating system cooperate to determine which bit of physical memory a memory access corresponds to, or they crash the program if there’s no such mapping). Attempts to read SGX data from outside an enclave receive special handling by the processor: reads always return a specific value (-1), and writes are ignored completely. The special handling is called “abort page semantics” and should be enough to prevent speculative reads from being able to learn anything.

However, the Foreshadow researchers found a way to bypass the abort page semantics. The data structures used to control the mapping of virtual-memory addresses to physical addresses include a flag to say whether a piece of memory is present (loaded into RAM somewhere) or not. If memory is marked as not being present at all, the processor stops performing any further permissions checks and immediately triggers the page fault mechanism: this means that the abort page mechanics aren’t used. It turns out that applications can mark memory, including enclave memory, as not being present by removing all permissions (read, write, execute) from that memory.

EDITED TO ADD: Intel has responded:

L1 Terminal Fault is addressed by microcode updates released earlier this year, coupled with corresponding updates to operating system and hypervisor software that are available starting today. We’ve provided more information on our web site and continue to encourage everyone to keep their systems up-to-date, as it’s one of the best ways to stay protected.

I think this is a comprehensive link to everything the company is saying about the vulnerability.

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Another Spectre-Like CPU Vulnerability

Google and Microsoft researchers have disclosed another Spectre-like CPU side-channel vulnerability, called “Speculative Store Bypass.” Like the others, the fix will slow the CPU down.

The German tech site Heise reports that more are coming.

I’m not surprised. Writing about Spectre and Meltdown in January, I predicted that we’ll be seeing a lot more of these sorts of vulnerabilities.

Spectre and Meltdown are pretty catastrophic vulnerabilities, but they only affect the confidentiality of data. Now that they — and the research into the Intel ME vulnerability — have shown researchers where to look, more is coming — and what they’ll find will be worse than either Spectre or Meltdown.

I still predict that we’ll be seeing lots more of these in the coming months and years, as we learn more about this class of vulnerabilities.

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Another Branch Prediction Attack

When Spectre and Meltdown were first announced earlier this year, pretty much everyone predicted that there would be many more attacks targeting branch prediction in microprocessors. Here’s another one:

In the new attack, an attacker primes the PHT and running branch instructions so that the PHT will always assume a particular branch is taken or not taken. The victim code then runs and makes a branch, which is potentially disturbing the PHT. The attacker then runs more branch instructions of its own to detect that disturbance to the PHT; the attacker knows that some branches should be predicted in a particular direction and tests to see if the victim’s code has changed that prediction.

The researchers looked only at Intel processors, using the attacks to leak information protected using Intel’s SGX (Software Guard Extensions), a feature found on certain chips to carve out small sections of encrypted code and data such that even the operating system (or virtualization software) cannot access it. They also described ways the attack could be used against address space layout randomization and to infer data in encryption and image libraries.

Research paper.

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Adding Backdoors at the Chip Level

Interesting research into undetectably adding backdoors into computer chips during manufacture: “Stealthy dopant-level hardware Trojans: extended version,” also available here:

Abstract: In recent years, hardware Trojans have drawn the attention of governments and industry as well as the scientific community. One of the main concerns is that integrated circuits, e.g., for military or critical-infrastructure applications, could be maliciously manipulated during the manufacturing process, which often takes place abroad. However, since there have been no reported hardware Trojans in practice yet, little is known about how such a Trojan would look like and how difficult it would be in practice to implement one. In this paper we propose an extremely stealthy approach for implementing hardware Trojans below the gate level, and we evaluate their impact on the security of the target device. Instead of adding additional circuitry to the target design, we insert our hardware Trojans by changing the dopant polarity of existing transistors. Since the modified circuit appears legitimate on all wiring layers (including all metal and polysilicon), our family of Trojans is resistant to most detection techniques, including fine-grain optical inspection and checking against “golden chips”. We demonstrate the effectiveness of our approach by inserting Trojans into two designs — a digital post-processing derived from Intel’s cryptographically secure RNG design used in the Ivy Bridge processors and a side-channel resistant SBox implementationĀ­ — and by exploring their detectability and their effects on security.

The moral is that this kind of technique is very difficult to detect.

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Spectre and Meltdown Attacks

After a week or so of rumors, everyone is now reporting about the Spectre and Meltdown attacks against pretty much every modern processor out there.

These are side-channel attacks where one process can spy on other processes. They affect computers where an untrusted browser window can execute code, phones that have multiple apps running at the same time, and cloud computing networks that run lots of different processes at once. Fixing them either requires a patch that results in a major performance hit, or is impossible and requires a re-architecture of conditional execution in future CPU chips.

I’ll be writing something for publication over the next few days. This post is basically just a link repository.

EDITED TO ADD: Good technical explanation. And a Slashdot thread.

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Acoustical Attacks against Hard Drives

Interesting destructive attack: “Acoustic Denial of Service Attacks on HDDs“:

Abstract: Among storage components, hard disk drives (HDDs) have become the most commonly-used type of non-volatile storage due to their recent technological advances, including, enhanced energy efficacy and significantly-improved areal density. Such advances in HDDs have made them an inevitable part of numerous computing systems, including, personal computers, closed-circuit television (CCTV) systems, medical bedside monitors, and automated teller machines (ATMs). Despite the widespread use of HDDs and their critical role in real-world systems, there exist only a few research studies on the security of HDDs. In particular, prior research studies have discussed how HDDs can potentially leak critical private information through acoustic or electromagnetic emanations. Borrowing theoretical principles from acoustics and mechanics, we propose a novel denial-of-service (DoS) attack against HDDs that exploits a physical phenomenon, known as acoustic resonance. We perform a comprehensive examination of physical characteristics of several HDDs and create acoustic signals that cause significant vibrations in HDDs internal components. We demonstrate that such vibrations can negatively influence the performance of HDDs embedded in real-world systems. We show the feasibility of the proposed attack in two real-world case studies, namely, personal computers and CCTVs.

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A Hardware Privacy Monitor for iPhones

Andrew “bunnie” Huang and Edward Snowden have designed a hardware device that attaches to an iPhone and monitors it for malicious surveillance activities, even in instances where the phone’s operating system has been compromised. They call it an Introspection Engine, and their use model is a journalist who is concerned about government surveillance:

Our introspection engine is designed with the following goals in mind:

  1. Completely open source and user-inspectable (“You don’t have to trust us”)

  2. Introspection operations are performed by an execution domain completely separated from the phone”s CPU (“don’t rely on those with impaired judgment to fairly judge their state”)

  3. Proper operation of introspection system can be field-verified (guard against “evil maid” attacks and hardware failures)

  4. Difficult to trigger a false positive (users ignore or disable security alerts when there are too many positives)

  5. Difficult to induce a false negative, even with signed firmware updates (“don’t trust the system vendor” — state-level adversaries with full cooperation of system vendors should not be able to craft signed firmware updates that spoof or bypass the introspection engine)

  6. As much as possible, the introspection system should be passive and difficult to detect by the phone’s operating system (prevent black-listing/targeting of users based on introspection engine signatures)

  7. Simple, intuitive user interface requiring no specialized knowledge to interpret or operate (avoid user error leading to false negatives; “journalists shouldn’t have to be cryptographers to be safe”)

  8. Final solution should be usable on a daily basis, with minimal impact on workflow (avoid forcing field reporters into the choice between their personal security and being an effective journalist)

This looks like fantastic work, and they have a working prototype.

Of course, this does nothing to stop all the legitimate surveillance that happens over a cell phone: location tracking, records of who you talk to, and so on.

BoingBoing post.

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