Some Of The Essential Aspects You Must Know About Rowhammer


What is Rowhammer?


A rowhammer is a type of threat or we can say a bug in dynamic random access memory (DRAM) that causes an effect on the neighboring row due to which it causes cross leak effect. Memory cell gets leak their charges and communicate electrically between themselves, which ultimately showing the content of neigbouring memory rows that was not there in the original DRAM. This effect can be due to electromagnetic intrusion. This type of susceptibility can be drawn out through Javascript, which enables attacker to get away from the web browser’s security sandbox and obtain access to the system.

The DRAM cells are embedded in rows and are organized very near to each other to increase density. Again and again activating rows of memory for writing data leads to leakage in electrical charge of a cell with its neighboring cell. It can affect the random bit flips and can change the memory content. Repeatedly access of rows leads to “hammering” a row and is therefore known as Row Hammering.

The embedded data in each of cells in DRAM lived-in separate memory cell that is electrically incorporated with one capacitor and one transistor. The charge nature of capacitor decides whether DRAM cell embed 1 or 0 as a binary value. Numbers of DRAM memory cells are closely tight into combined circuits that arrange the cells for reading, writing as well as refreshing data.

It is repeatedly possible to cause bits to flips in dynamic random access memory (DRAM) by writing to them frequently and from two rows in DRAM to active the rows and causes bit flips which can be introduced in rows up to 9 rows far from these two attacker rows and the 9 rows are known as sufferer rows. Most of the leakage is occurred between the neighboring rows immediately next to an attacker rows. Using two neighbor rows to encompass rows with hammer is known as amplified single sided hammering which can be useful in exploitation (JavaScript).

Thus difficulty was often faced with RAM manufactured after 2010. More than 75% of RAM from the sample of 130 RAM modules from 3 manufacturers are susceptible. DDR4 ram is also susceptible with 8 out of 12 sampled module DRAMs which were causing bit flips and certain design in the DRAM rows leads to bit flips. The RAM modules manufactured after 2012 was being susceptible.

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