Inception: A simple XOR can cause a Microarchitectural Stack Overflow

Re:Inception: A simple XOR can cause a Microarchitectural St... by ireallywantthat on Tuesday August 08, 2023 @02:55PM (#37053786)

> Instead of flushing the entire branch predictor state, AMD proposed a different mitigation for the Linux kernel. By reducing all returns in the kernel to a single one, it becomes possible to ensure a safe (but still incorrect) branch predictor state each time this return is executed. Keeping previous mitigations in mind, this effectively means that AMD opted to have all indirect branches forcibly mispredict to a benign location, preventing Inception attacks.

So, There will be no decrease in performance or any other performance impact if you are running Linux kernel.

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Re:Inception: A simple XOR can cause a Microarchitectural St... by duskwuff on Tuesday August 08, 2023 @03:34PM (#37054339)

As I understand it, there is likely to be a performance decrease when executing indirect branches within the kernel.

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Re:Inception: A simple XOR can cause a Microarchitectural St... by mjevans on Tuesday August 08, 2023 @03:55PM (#37054621)

My understanding (which could be incorrect) is that the single return location clobbers the branch predictor's leaked data with static and (attack) worthless data without completely clearing the rest of the prediction cache.

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Re:Inception: A simple XOR can cause a Microarchitectural St... by duskwuff on Tuesday August 08, 2023 @04:24PM (#37054993)

Right, which means the CPU can't effectively predict indirect branches (like calls through function pointers, or certain types of switch statements).

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