3 ms·
> NO_SMT disables Simultaneous multithreading (SMT), the CPU feature better known under Intel’s trade name of “Hyper-Threading”. SMT allows a CPU core to execut
by sillysaurusx 5y ago
> NO_SMT disables Simultaneous multithreading (SMT), the CPU feature better known under Intel’s trade name of “Hyper-Threading”. SMT allows a CPU core to execute two or more threads at the same time, for improved performance at the cost of contention for per-core resources, such as caches, TLBs etc.
> Letting multiple threads share invisible resources carries the risk of letting a malicious thread steal secrets from a “sibling” thread running on the same core—a risk that over the years has materialized into multiple attacks, like TLBleed, PortSmash, Fallout, ZombieLoad, RIDL. A straightforward mitigation for this entire family of attacks, past and future, is then to simply disable SMT, which is what NO_SMT does.
BAHAHA cperciva was right! It’s a decade later and people care now! Linus didn’t care at the time!
I’m on mobile otherwise I’d link to relevant refs, but it was an “I told you so” 10 years in the making. Maybe longer? When was cperciva’s cache stealing research?
- gregsadetsky 5y agoDiscussed here: https://news.ycombinator.com/item?id=16082909 https://news.ycombinator.com/item?id=16082909 cperciva's paper from 2005 (linked above): http://www.daemonology.net/papers/htt.pdf http://www.daemonology.net/papers/htt.pdf
- sillysaurusx 5y agoHmm. That commenter’s username seems familiar… Thanks. :) > The problems introduced by caches have been further exacerbated by the current trend towards increased parallelism. On recent processors implementing simultaneous multithreading [18], such as Intel’s “Hyper- Threading” processors [11], access to the L1 cache is shared between two independent instruction streams And here we are 16 years later, with NO_SMT. Neat. Perhaps my emotional outburst wasn’t substantive, but boy was it satisfying. I’ll try to restrain such urges in the future, but somehow I doubt a 16 year “told ya so” will pop up again any time soon. It’s half as old as I am. I wish I could remember Linus’ remark about cperciva’s attack being merely “theoretical.”
- gregsadetsky 5y agohttps://lkml.org/lkml/2005/5/16/152 https://lkml.org/lkml/2005/5/16/152 Linus: "[...] I'd be really surprised if somebody is actually able to get a real-world attack on a real-world pgp key usage or similar out of it (and as to the covert channel, nobody cares). It's a fairly interesting approach, but it's certainly neither new nor HT-specific, or necessarily seem all that worrying in real life. [...]"
- mzs 5y agoHow many years until this from last year is regretted? introduce memfd_secret system call to create "secret" memory areas v11: * Drop support for uncached mappings https://lwn.net/ml/linux-kernel/20201124092556.12009-1-rppt@kernel.org/ https://lwn.net/ml/linux-kernel/20201124092556.12009-1-rppt@...