New ZenHammer Attack Bypasses Rowhammer Defenses on AMD CPUs

Cybersecurity researchers from ETH Zurich have developed a new variant of the RowHammer DRAM (dynamic random-accessibility memory) attack that, for the 1st time, successfully performs in opposition to AMD Zen 2 and Zen 3 methods in spite of mitigations these as Target Row Refresh (TRR).

“This consequence proves that AMD devices are similarly susceptible to Rowhammer as Intel units, which greatly increases the attack area, taking into consideration modern AMD industry share of around 36% on x86 desktop CPUs,” the scientists stated.

The approach has been codenamed ZenHammer, which can also set off RowHammer little bit flips on DDR5 products for the initially time.

RowHammer, first publicly disclosed in 2014, is a well-identified attack that exploits DRAM’s memory mobile architecture to alter info by frequently accessing a certain row (aka hammering) to lead to the electrical demand of a mobile to leak to adjacent cells.

This can induce random bit flips in neighboring memory rows (from to 1, or vice versa), which can change the memory contents and likely facilitate privilege escalation, compromising process qualifications, integrity, and availability of a system.

The attacks acquire benefit of the bodily proximity of these cells within just the memory array, a difficulty that’s probably to worsen as the DRAM technology scaling carries on and the storage density will increase.

“As DRAM carries on to scale, RowHammer bit flips can manifest at more compact activation counts and hence a benign workload’s DRAM row activation prices can tactic or even exceed the RowHammer threshold,” ETH Zurich researchers pointed out in a paper printed in November 2022.

“As a result, a technique might expertise little bit flips or frequently set off RowHammer protection mechanisms even without the need of a destructive party accomplishing a RowHammer attack in the program, top to facts corruption or major effectiveness degradation.”

One of the essential mitigations executed by DRAM producers against RowHammer is TRR, which is an umbrella expression made use of for mechanisms that refresh goal rows that are identified to be accessed commonly.

In undertaking so, the notion is to deliver more memory refresh operations so that victim rows will both be refreshed ahead of bits are flipped or be corrected immediately after bits are flipped due to RowHammer attacks.

ZenHammer, like TRRespass and SMASH, bypasses TRR guardrails by reverse engineering the magic formula DRAM handle functions in AMD techniques and adopting enhanced refresh synchronization and scheduling of flushing and fencing directions to result in bit flips on 7 out of 10 sample Zen 2 devices and six out of 10 Zen 3 gadgets.

The analyze also arrived at an optimum hammering instruction sequence to strengthen row activation costs in get to facilitate far more helpful hammering.

“Our results confirmed that typical masses (MOV) with CLFLUSHOPT for flushing aggressors from the cache, issued promptly immediately after accessing an aggressor (‘scatter’ type), is exceptional,” the scientists reported.

ZenHammer has the distinction of being the extremely to start with process that can result in little bit flips on devices outfitted with DDR5 chips on AMD’s Zen 4 microarchitectural platform. That mentioned, it only functions on one particular of the 10 analyzed units (Ryzen 7 7700X).

It can be value noting that DDR5 DRAM modules were formerly viewed as immune to RowHammer attacks owing to them replacing TRR with a new kind of defense referred to as refresh administration.

“The alterations in DDR5 such as improved RowHammer mitigations, on-die mistake correction code (ECC), and a larger refresh fee (32 ms) make it more durable to trigger little bit flip,” the scientists reported.

“Given the lack of bit flips on 9 of 10 DDR5 units, much more get the job done is essential to improved comprehend the potentially new RowHammer mitigations and their security ensures.”

AMD, in a security bulletin, claimed it really is evaluating RowHammer little bit flips on DDR5 equipment, and that it will supply an update next its completion.

“AMD microprocessor products and solutions involve memory controllers built to fulfill field-regular DDR specifications,” it extra. “Susceptibility to RowHammer attacks differs dependent on the DRAM machine, seller, technology, and system configurations.”

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Some parts of this posting are sourced from:
thehackernews.com