Spectre rears its ugly head again as researchers show some RISC-V chips are susceptible

security

Eight years on, we're still paying to hide the future glimpsed during speculative execution

If you thought that the famous Spectre security vulns were a relic of 2018, think again. Certain RISC-V chips are still very much subject to this hair-raising hole, researchers say.Spectre refers to a family of vulnerabilities related to speculative execution, a performance optimization technique based on predicting the flow of data before instructions have been executed. Incorrect predictions get rolled back without affecting running applications but nonetheless leave traces that can be recovered and exploited to violate memory protections and access secrets.Spectre flaws have dogged x86 and ARM chips for years, leading computer scientists to develop a series of defenses, including Indirect Branch Restricted Speculation (IBRS), Indirect Branch Prediction Barrier (IBPB), and Single Thread Indirect Branch Predictor (STIBP).

Researchers affiliated with academic institutions in Belgium and Germany say that it's been popular to assume that the RISC-V chip architecture isn't affected by Spectre vulnerabilities because it's too simple.

That assumption is incorrect, according to a paper accepted at the 35th Usenix Security Symposium, "Spectre on RISC-V Silicon: Attacks and Defenses on Commercial Out-of-Order Processors." It says that commercially available out-of-order RISC-V processors (SiFive P550 and T-Head Xuantie C910/C920) are vulnerable to all major Spectre variants.RISC-V processors that process instructions in-order (SiFive U74, Xuantie C906, C908) do not appear to be vulnerable.Prior research has shown that RISC-V processors used for academic research (e.g. BOOM, RiscyOO, RSD, Proteus, NaxRiscv, and NutShell) can be affected by one or more of the Spectre variants, but hasn't addressed commercial silicon."We demonstrate proof-of-concept attacks on both processors using Spectre-PHT, Spectre-BTB, SpectreRSB, and Spectre-STL, achieving up to 100 percent recall with more than 97 percent precision," the paper states. Spectre-PHT involves mistraining the Pattern History Table; Spectre-BTB poisons the Branch Target Buffer; Spectre-RSB attacks the Return Stack Buffer; and Spectre-STL (Store To Load) exploits mispredicted store-to-load forwarding.