MIT boffins' TONTOU attack slips through Spectre defenses on Intel and AMD CPUs
Timer interrupts reopen branch predictor poisoning window, with a working Zen 2 exploit to prove it
Two MIT researchers will present a new speculative execution attack at DEF CON 34 that uses precisely timed interrupts to bypass defenses against Spectre v2.
Daniël Trujillo and Mengjia Yan of MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) shared their paper [PDF] with The Register ahead of publication. Their attack targets mitigations designed to neutralize potentially hostile branch predictor states before sensitive code runs.
Such neutralization is an important defense against Spectre-style attacks. Depending on the mitigation, the processor or operating system isolates, clears, or safely retrains relevant predictor state when entering privileged code or shortly before a protected branch executes.
Different chipmakers deploy neutralization mitigations slightly differently. Intel's eIBRS sanitizes branch predictors upon context switch, while AMD's Safe RET, introduced after the Inception attack Trujillo co-authored in 2023, focuses on the...
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