Jul 10 2018

New Spectre-like attack uses speculative execution to overflow buffers

Enlarge (credit: Aurich Lawson / Getty Images)

When the Spectre and Meltdown attacks were disclosed earlier this year, the expectation was that these attacks would be the first of many, as researchers took a closer look at the way that the speculative execution in modern processors could be used to leak sensitive information and undermine the security of software running on those processors. In May, we saw the speculative store bypass, and today we have a new variant on this theme: speculative buffer overflows, discovered by Vladimir Kiriansky at MIT and independent researcher Carl Waldspurger.

All the attacks follow a common set of principles. Each processor has an architectural behavior (the documented behavior that describes how the instructions work and that programmers depend on to write their programs) and a microarchitectural behavior (the way an actual implementation of the architecture behaves). These can diverge in subtle ways. For example, architecturally, a program that loads a value from a particular address in memory will wait until the address is known before trying to perform the load. Microarchitecturally, however, the processor might try to speculatively guess at the address so that it can start loading the value from memory (which is slow) even before it's absolutely certain of which address it should use.

If the processor guesses wrong, it will ignore the guessed-at value and perform the load again, this time with the correct address. The architecturally defined behavior is thus preserved. But that faulty guess will disturb other parts of the processor—in particular the contents of the cache. These microarchitectural disturbances can be detected and measured, allowing a malicious program to make inferences about the values stored in memory.

Read 12 remaining paragraphs | Comments

May 22 2018

New speculative-execution vulnerability strikes AMD, ARM, and Intel

Intel Skylake die shot. (credit: Intel)

A new attack that uses processors' speculative-execution capabilities to leak data, named Speculative Store Bypass (SSB), has been published after being independently discovered by Microsoft's Security Response Center and Google Project Zero. Processors from Intel and AMD, along with some of those using ARM's designs, are all affected.

Since the Meltdown and Spectre flaws were announced earlier this year, the speculative and predictive capabilities of modern microprocessors have been closely examined, revealing several new attacks.

All the attacks follow a common set of principles. Each processor has an architectural behavior (the documented behavior that describes how the instructions work and that programmers depend on to write their programs) and a microarchitectural behavior (the way an actual implementation of the architecture behaves). These can diverge in subtle ways. For example, architecturally, a program that loads a value from a particular address in memory will wait until the address is known before trying to perform the load. Microarchitecturally, however, the processor might try to speculatively guess at the address so that it can start loading the value from memory (which is slow) even before it's absolutely certain of which address it should use.

Read 8 remaining paragraphs | Comments

Apr 11 2018

AMD systems gain Spectre protection with latest Windows fixes

Enlarge / An AMD Ryzen. (credit: Fritzchens Fritz)

The latest Windows 10 fixes, released as part of yesterday's Patch Tuesday, enable protection against the Spectre variant 2 attacks on systems with AMD processors.

Earlier this year, attacks that exploit the processor's speculative execution were published with the names Meltdown and Spectre, prompting a reaction from hardware and software companies. AMD chips are immune to Meltdown but have some vulnerability to the two Spectre variants. Spectre variant 1 requires application-level fixes; variant 2 requires operating system-level alterations.

Both Intel and AMD have released microcode updates to alter their processor behavior to give operating systems the control necessary to protect against Spectre variant 2. Microsoft has been shipping the Intel microcode, along with the operating system changes necessary to use the microcode's new features, for several weeks now; with yesterday's patch, similar protections are now enabled on AMD machines.

Read 2 remaining paragraphs | Comments

Apr 04 2018

Intel drops plans to develop Spectre microcode for ancient chips

Enlarge / A Sandy Bridge wafer. Sandy Bridge is the oldest chip family that's guaranteed to get Spectre variant 2 fixes. (credit: Intel)

Intel has scaled back its plans to produce microcode updates for some of its older processors to address the "Spectre variant 2" attack. Core 2 processors are no longer scheduled to receive updates, and, while some first generation Core products have microcode updates available already, others have had their update cancelled.

Earlier this year, attacks that exploit the processor's speculative execution were published with the names Meltdown and Spectre, prompting a reaction from hardware and software companies.

The Spectre attack has two variants, numbered version 1 and version 2. Spectre version 1 attacks will need software fixes, and the nature of these attacks means that they may always need software fixes. Version 2 is amenable to hardware and firmware fixes.

Read 5 remaining paragraphs | Comments