Google Presented a New Attack Technique for DRAM Memory


Google has introduced a new Rowhammer attack on dram memory that allows an attacker to bypass existing protection methods and cause bit flips in more rows of memory. Memory chips are organized in a sort of grid pattern of "rows" and "columns".


In recent years, memory chips have acquired an ever-increasing capacity, with the memory cells being placed ever closer together. This reduces costs, but cell density negatively affects memory reliability. This density ensures that the cells can influence each other.


Repeatedly accessing memory rows can corrupt data in adjacent rows. Rowhammer causes bits in adjacent rows to be "flipped" when accessing a memory row repeatedly. By flipping these bits, it is ultimately possible for an attacker on a system to gain read-write access to the entire physical working memory, after which it is possible, for example, to gain kernel rights.


The first Rowhammer attack was demonstrated against DDR3 memory. To prevent such attacks, memory manufacturers took a variety of measures in DDR4 memory, which is used by modern systems and telephones. Those measures appear to work against the original Rowhammer attack, but are vulnerable to new variants.


One of these variants was demonstrated last year by researchers from VU University Amsterdam. Now Google has also developed a new attack. This attack is called Half-Double . Unlike the original Rowhammer attack, where bit flips are only possible at a distance of one memory row, leaving only the adjacent memory rows to attack, Half-Double makes it possible to adjust bits in more distant memory rows.



According to Google , the attack is possible because the distance between rows of dram memory keeps getting smaller. The tech company has consulted with parties in the semiconductor industry to find solutions for the Rowhammer phenomenon. "We publish this study because we believe it increases knowledge about the Rowhammer phenomenon and will help researchers and industry partners alike develop solutions together," said Salman Qazi of Google.

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