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Saint Branch Target Reuse, Who Reused the Jump Predictions
Patron of JIT compilers, branch predictions left in the cache, and Spectre mitigations never quite finished.
Life
On 29 September 2026 the VUSec group, with Scuola Superiore Sant'Anna, revealed Branch Target Reuse, a new Spectre-v2 variant against JIT engines. When a JIT frees and reuses its own code cache, the old indirect-branch predictions can linger, causing speculative execution of the previous code. On Linux, on recent Intel processors, the researchers recovered the root password hash in a few minutes; they confirmed the flaw on Intel, AMD and Arm.
Prayer
O Saint Branch Target Reuse, who revive the jumps already freed, let our JITs forget the code that no longer exists. Amen.
How to celebrate
Celebrated by updating the kernel with the IBPB mitigation on JIT reuse and following the CPU vendors' guidance.
A jump reused, a secret speculated.