Understanding The Meltdown And Spectre Exploits: Intel, AMD, ARM, And Nvidia

After two days of whirlwind developments, we finally have more of a complete picture of the new vulnerabilities that impact processors from the leading vendors. Reports initially surfaced two days ago that Intel's processors are susceptible to a new hardware-based bug that cannot be patched with a mere microcode update. A report from The Register, based in part on a blog post, said that incoming Windows and Linux patches would correct the vulnerability but come with a 5-30% performance loss depending on the workload.

The industry remained silent due to NDAs that were scheduled to expire on January 9, the same date as a round of patches were scheduled to appear. After a day of silence while its stock slumped, Intel issued a statement and claimed the issue is not a hardware bug. Intel also announced that it's working with other titans of the industry, such as AMD and ARM Holdings, to "develop an industry-wide approach to resolve this issue promptly and constructively." AMD has since released a statement and claimed that it has minimal exposure to the primary vulnerability.

The root issues behind the vulnerabilities weren't clearly defined at the time, but a slew of releases from several of the parties involved, along with Google's Project Zero team, have shed light on two new exploits that have served as the catalyst for the recent developments. We'll cover the new exploits below; then we'll get to the updates from Intel, ARM, AMD, and Nvidia.

Performance First

Before we dive into the nuts and bolts, recent tests indicate the patch does not impart a cataclysmic performance loss in most workloads. Phoronix tested the Linux patch, and Computerbase.de tested a patched Windows Insider build.

The good news? Most desktop applications appear to be safe in both Windows 10 and Linux. That includes most workloads that are largely confined to the user space, such as gaming and normal productivity applications. There does appear to be a slowdown to storage I/O operations (2-7%), but for now it's hard to ascertain if that is due to the patch or other kernel updates. The Windows 10 patch was rolled out to the Windows Insider builds in November, and there haven't been reports of performance issues.

The bad news? The patch does incur a performance overhead to some enterprise applications. Phoronix recorded significant performance regressions in the object-relational PostgreSQL database. Redis also suffers a performance loss. Many industry analysts feel the real impacts will come in virtualized environments, but we have yet to see benchmarks. Google has already updated all its cloud infrastructure, which includes its cloud computing services, and we haven't yet heard of significant user backlash due to reduced performance.

Meet Meltdown & Spectre

Google's Project Zero touched off the vulnerability scare when it discovered that it could access data held in the protected kernel memory through two exploits that are now known as Meltdown and Spectre. Google does not believe these exploits have ever been used in the wild, but it's impossible to tell if they have or not.

Meltdown is both easy to execute and easy to fix. This exploit allows applications to read from the protected kernel memory. That ability can allow hackers to read passwords, encryption keys, or other data from the memory. Intel's statement specifically noted that the exploits cannot corrupt, modify, or delete data, but those points are moot if the attacker can access passwords and encryption keys. The biggest concern for data centers and cloud service providers is that the exploit also allows an application resident in one virtual machine to access the memory of another remote virtual machine. This means an attacker could rent an instance on a public cloud and collect information from other virtual machines on the same server.

Researchers have been able to execute a Meltdown exploit only on Intel processors, although ARM has submitted patches to protect itself from the same method of attack. In fact, the attack exploits Intel's out-of-order execution implementation that is present on every Intel processor made since 1995. Researchers discovered Meltdown last year. The exploit is reportedly simple enough that a script kiddie could execute the attack, so a fix is of utmost importance.

Apple already patched this exploit in the MacOS December OSX patch (10.13.2). Windows is also pushing emergency patches out immediately. The Linux kernel has also been patched. These patches do have performance impacts, as we noted above, that largely revolve around how frequently the application issues kernel calls. 

The Spectre exploit is much more nefarious and impacts Intel, AMD, and ARM. This exploit can access kernel memory or data from other applications. Researchers contend that fixing this exploit would require a fundamental re-tooling of all processor architectures, so we'll live with the threat of this vulnerability for the foreseeable future. Fortunately, this exploit is extremely hard to execute and requires an elevated level of knowledge of the interior workings of the target processor.

These two exploits are categorized into three variants. Variants 1 and 2 are Spectre, whereas Variant 3 is Meltdown. Intel is vulnerable to all three.

Variant 1: bounds check bypass (CVE-2017-5753) Variant 2: branch target injection (CVE-2017-5715) Variant 3: rogue data cache load (CVE-2017-5754)

Levels Of Exposure

We reached out to AMD, and the company responded with the following information, which has since been publicly released.

Most notably, AMD claims that is has zero vulnerability to Variant 3 (Meltdown), stating that the patches that are currently being issued for Meltdown do not apply to its processors due to "architectural differences." This is excellent news for AMD, as it therefore has no exposure to the current round of potentially performance-sapping patches. That bodes very well for the company as it reenters the data center with a competitive line of EPYC processors.

The Ryzen desktop processors are also not susceptible to Meltdown. Linus Torvalds has also granted AMD an exemption to the performance penalties incurred by the Linux patch for Meltdown.

AMD is vulnerable to Variant 1, which is a Spectre exploit. As noted above, many contend that Spectre is not likely to see an effective patch any time soon, and some researchers claim the vulnerability exists in every modern processor architecture in existence. They also claim that fixing the issues could require a redesign of fundamental processor architectures. AMD said it has a patch that can mitigate Variant 1 with minimal performance impact and further stated that it has a "near zero risk of exploitation" from Variant 2, which is also a Spectre exploit.

Nvidia also issued a statement regarding the vulnerabilities:

Nvidia’s core business is GPU computing. We believe our GPU hardware is immune to the reported security issue and are updating our GPU drivers to help mitigate the CPU security issue. As for our SoCs with ARM CPUs, we have analyzed them to determine which are affected and are preparing appropriate mitigations.

ARM Holdings has added a security update to its website that outlines its exposure to the vulnerabilities, and like Intel, it is susceptible to all three variants. 

The legal ramifications of these developments could be troublesome. The Law Offices of Howard G. Smith has already announced an investigation on behalf of Intel Corporation investors, and there will likely be more similar developments in the coming weeks. Intel has a history of establishing a reserve to cover pending large-scale hardware replacements, but the company has not disclosed a new fund to deal with the vulnerabilities. The company has also stated that it does not expect any impact to its business.

Intel's statement on the matter specifically says that the exploits are not caused by a "bug" or a "flaw" that is unique to Intel products. Intel also noted that the exploits can "gather sensitive data from computing devices that are operating as designed." These statements likely indicate Intel will defend any potential claims because "the hardware is working correctly." Depending on when these vulnerabilities became known (some claim that Meltdown-type attacks have been a known entity since 2010), these points may be challenged in court. ARM and other vendors may also face similar challenges.

Intel's CEO, Brian Krzanich, also sold $39 million in stocks in November 2017 (this doesn't include the amount he paid for the stock options). These transaction initially appeared innocuous (and they may be) because Krzanich sold the stock under a 10b5-1(c) plan, which is a pre-planned sale of stocks intended to prevent claims of insider trading. The sale left Krzanich with the Intel-mandated minimum of 250,000 stocks. The sale was pre-planned on October 30. Now, though, MarketWatch claims Intel was made aware of the vulnerability on June 1, which may draw attention to the matter from regulatory officials. Business Insider said a representative for the Securities and Exchange Commission declined to comment on the matter.

Considering the lengthy preparation period, we imagine there will not be any major service disruptions to the cloud service providers. However, we expect more details to come to light concerning performance impacts of the new patches on various workloads. Stay tuned.

Paul Alcorn
Managing Editor: News and Emerging Tech

Paul Alcorn is the Managing Editor: News and Emerging Tech for Tom's Hardware US. He also writes news and reviews on CPUs, storage, and enterprise hardware.

  • bennie101
    Wow that hard earn money we spent on intel cpus will come at a bigger cost now. I am sure they have know this issues for well over 20 years but Greed is the ROOT of aLL EVIL.
  • jeremiah.moss
    A lot of people are claiming that gaming won't be affected, but that confuses me. You're making a lot calls from user space to the drivers, which should be in kernel space. We're not accessing the GPU from user mode directly, are we? Isn't this going through drivers and / or the HAL?
  • -Fran-
    20557284 said:
    A lot of people are claiming that gaming won't be affected, but that confuses me. You're making a lot calls from user space to the drivers, which should be in kernel space. We're not accessing the GPU from user mode directly, are we? Isn't this going through drivers and / or the HAL?

    The problem lies (becomes exploitable) when you move in and out of memory spaces. So, if you don't have a malware running already and you are gaming, if the/a malware tries to access something without you making it run or force a switch of programs, nothing will happen since no memory will be moving (no randomized movement of memory addresses happen). So, the stuff put in the user memory address space will remain there without actually calling anything "new" to be put there from the kernel space (drivers should really be loaded at the start and not during gameplay). Now, for Streaming though. You are forcing several context switches there, so it will be interesting to see if it happens. The DX driver needs to send the data to another program residing in a different user space, so that implies moving memory.

    That is how I understand this problem, so feel free to correct me.

  • Mark RM
    Article was logical and well constructed, easy to follow and put the information in one place. Nicely done.Good piece of journalism there.
  • ET3D
    Is there any indication that the Microsoft patch doesn't inflict an unneeded slowdown on AMD hardware? I know that Linus stopped that on the Linux side, but who's to say that Microsoft didn't just apply the fix to all architectures?

    20557284 said:
    We're not accessing the GPU from user mode directly, are we?

    Yes we are. That's what Microsoft changed in the driver model between XP and Vista. There is still a kernel component to the drivers, but much of the work is done in user mode, which both adds to OS stability (early NVIDIA Vista drivers notwithstanding) and benefits performance.
  • InvalidError
    20557284 said:
    A lot of people are claiming that gaming won't be affected, but that confuses me. You're making a lot calls from user space to the drivers, which should be in kernel space. We're not accessing the GPU from user mode directly, are we?
    Most of the DirectX and other APIs' runtime is user-space and that's what typical software interacts with the most. Not every DirectX call results in a trip through a system call.

    In the case of server-style workloads that frequently involve the file system, IO and inter-process synchronization though, most of those have a very thin APIs that do little more than populate structures and do basic sanity checks before doing system calls.
  • Myrmidonas
    I do not want to play the "devil's advocate" but, if he knew about the fault since last June he wouldn't sell on purpose for the case he would be accused for "abandoning ship" before it sinks. After all he is CEO from since May 2013. The flaws are rumored to be on most intel's chips many years before.
  • anbello262
    Who bough intel stocks after the bug was announced? Was a ver good time for that!
  • cryoburner
    Intel's statement on the matter specifically says that the exploits are not caused by a "bug" or a "flaw" that is unique to Intel products. Intel also noted that the exploits can "gather sensitive data from computing devices that are operating as designed."
    Exactly, it's not a bug. The backdoor has been functioning perfectly for decades. : 3
  • redgarl
    Well, after Volkswagen scam, we have the Intel scam. It really doesn't look good for them in the fore coming future.