  Memory isolation is critical for system reliability, security, and safety.
Unfortunately, read disturbance can break memory isolation in modern DRAM
chips. For example, RowHammer is a well-studied read-disturb phenomenon where
repeatedly opening and closing (i.e., hammering) a DRAM row many times causes
bitflips in physically nearby rows.
  This paper experimentally demonstrates and analyzes another widespread
read-disturb phenomenon, RowPress, in real DDR4 DRAM chips. RowPress breaks
memory isolation by keeping a DRAM row open for a long period of time, which
disturbs physically nearby rows enough to cause bitflips. We show that RowPress
amplifies DRAM's vulnerability to read-disturb attacks by significantly
reducing the number of row activations needed to induce a bitflip by one to two
orders of magnitude under realistic conditions. In extreme cases, RowPress
induces bitflips in a DRAM row when an adjacent row is activated only once. Our
detailed characterization of 164 real DDR4 DRAM chips shows that RowPress 1)
affects chips from all three major DRAM manufacturers, 2) gets worse as DRAM
technology scales down to smaller node sizes, and 3) affects a different set of
DRAM cells from RowHammer and behaves differently from RowHammer as temperature
and access pattern changes.
  We demonstrate in a real DDR4-based system with RowHammer protection that 1)
a user-level program induces bitflips by leveraging RowPress while conventional
RowHammer cannot do so, and 2) a memory controller that adaptively keeps the
DRAM row open for a longer period of time based on access pattern can
facilitate RowPress-based attacks. To prevent bitflips due to RowPress, we
describe and evaluate a new methodology that adapts existing RowHammer
mitigation techniques to also mitigate RowPress with low additional performance
overhead. We open source all our code and data to facilitate future research on
RowPress.
