January 10th, 2018

Spectre and Meltdown

Will Spectre and Meltdown be the flagship computer security crisis of 2018? There is a good chance that it will be, although I doubt that many personal computer users will be directly affected.

Good news

These flaws are hard to understand and take advanced engineering skills to implement; when implemented they are hard to exploit; I struggle to imagine results that would be worth a hacker’s trouble. Also, exploiting these flaws on a computer you do not already have access to is close to impossible. Consequently, good basic computer hygiene will protect you from these attacks as well as everything else thrown at you. In addition, the exploits are read-only; they do not corrupt data or processes.

The patches are going out this week to all the major operating systems and so far, the bruited predictions of devastating across-the-board 30% performance degradations have not proven out. 10% degradation and only in limited circumstances seems more realistic according to early testing reports.

Less good news

Nevertheless, the fallout from Spectre and Meltdown is likely to cause migraines and insomnia among computer security experts for months, even years to come. And the picture is not quite as rosy for businesses, especially for businesses that rely on virtual computing in various forms, as it is for individuals.

Scope

These are not your garden variety zero-day exploits. When I wrote about KRACK a few months ago, I explained that the flaw is particularly bad because it is in the standard and every correct implementation is vulnerable. The Spectre and Meltdown flaws are in the processor chip design. Intel processors have the worst problems and they perform the vast majority of computer processing in the world today, but AMD and ARM processors are also affected. That covers most of the rest of computing, including phones and tablets. For reasons I will elaborate on later, I suspect other processors have not been cited only because no one has looked hard enough yet.

The patches that have been applied are crack sealers; they do not repair the broken foundation that caused the cracks. Fixing the source of the cracks will require new processor designs and new chips. In order to explain just what Spectre and Meltdown are, I have to explain several unfamiliar concepts.

Protection rings

One of the pillars of computer security is called a “protection ring.” They are what prevents one computer process from interfering with another. For example, without protection rings, forcing a user to pass through a login gate before using a computer is easier to circumvent. Protection rings have been built right into the silicon of most processors since the eighties and the concept goes back to the beginnings of multi-processing in the 60s.

To science fiction readers, I liken protection rings to Asimov’s laws of robotics—they are intended to be intrinsic in all computers. In theory, protection rings when properly used make it impossible to break into a well-written operating system without physically altering the processor. When a computer is hacked into, it usually stems from a flaw in the operating system’s use of protection rings, not the physical processor chip.

The Spectre and Meltdown flaws are special because they are gaps in the integrity of privilege rings that were inadvertently built into the processor chips. To see how these gaps were opened, we have to look at concepts of modern processor design.

Multi-core processors

One of these concepts is “multi-core processors.” Before the advent of multi-cores, the capacity of processors was beginning to be limited by the great physical speed limit: the speed of light. When a processor reaches a certain number of instructions per second, it is limited by the time a signal takes to travel across the chip at the speed of light. The processor can’t move on to the next instruction in less time than it takes to read he previous instruction’s results.

Processor designers got around that by putting multiple processors, cores, on a single chip. In theory, by putting two cores on a chip, the speed is doubled. But that does not really solve the problem because taking advantage of the doubled speed requires complex and expensive changes in program design.

Speculative execution

The designers hit on a solution to this: speculative execution. Most computer programs are long chains of “if-thens”. If X condition is met, do Y; if it is not met, do Z. Traditional computers first evaluate X, then decide whether to perform Y or Z. With speculative execution, at the same time one core evaluates X, another core performs Y, and a third performs Z. Depending on how X comes out, Y or Z is discarded. This is a gross simplification, but in the time a single core uses to evaluate X, the three cores already have both the Y and Z results. Thus, the multi-core processor executes a conventionally written program in much less time than a single core. And the speed of computing doubles in 18 months again. Nifty, huh?

Not so nifty. Those discarded speculative chunks of execution can be manipulated in such a way that protection rings are violated. I won’t go into how it’s done. A Google researcher explains it here.

Migraines and insomnia

I am not optimistic when I think about what these defects reveal about processor design. Software development underwent a revolution in the early part of this century when security rose in priority. You can read about it in my book, Personal Cybersecurity. Security was a neglected step-child in the pioneering days of software development in the last century, but around 2000, the industry realized that computing would die if software was not built with more secure methodologies. The revolution is still going on, but the slap-dash attitude toward security that characterized the software cowboys of the 90s is gone.

Spectre and Meltdown tell me that the security revolution did not make it into processor design. Makes you think about why the CEO of Intel sold a big block of Intel stock after the flaws in Intel chips were discovered.

I am afraid we have not heard the last of chip level security flaws. I hope processor designs are not easy pickings for hackers, but the fact that these flaws have been present for at least a decade is daunting. Also, to completely eradicate these flaws, processor chips or entire computers will have to be replaced, which suggests that heads will ache on for years.

Coming soon

I wrote a blog on hypervisor hacking and one on virtual machine security for Network World last year that are affected by the Spectre and Meltdown flaws, but I’ll save comments on the safety of virtual computing for another blog.

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