GoFetch

What is a Cache Side-Channel Attack?

Modern processors use caches to reduce a program's memory access latency. If data has been accessed before, it gets cached, which makes subsequent accesses to it faster. Since the cache is shared by processes running on the same machine, attackers co-located to the same machine can monitor the cache's state to deduce a victim's access pattern.

What is constant-time programming?

Constant-time programming is a paradigm that aims to harden code against side-channel attacks by ensuring that all operations take the same amount of time, regardless of their operands. In particular, constant-time code cannot contain secret-dependent branches, loops, or other control structures.

What is a data memory-dependent prefetcher?

Prefetchers are a hardware optimization that predicts memory addresses to be accessed in the near future and fetches the data into the cache accordingly from the main memory. To make a prediction, classical prefetchers use the address trace of previous demand accesses. This strategy performs poorly when it comes to irregular access patterns like linked-list traversals.

Are there other DMP-vulnerable cryptographic implementations?

We don't know. Our attack relies on the fact that it is possible to craft inputs to control specific intermediate states, making them contain memory addresses in a key-dependent way. The DMP then serves as an oracle, allowing us to learn if the intermediate state indeed looks like a pointer and thus leaks secret key bits.

Can the DMP be disabled?

Yes, but only on some processors. We observe that the DIT bit set on m3 CPUs effectively disables the DMP. This is not the case for the m1 and m2. Also, Intel's counterpart, DOIT bit, can be used to disable DMP on the Raptor Lake processors. Update (April 2024): A HID configuration bit (SYS_APL_HID11_EL1[30]) was found by Hector Martin (marcan) to disable DMPs on m1 and m2 CPUs.