Stuffing the return stack buffer [LWN.net]

Stuffing the return stack buffer

Posted Jul 26, 2022 0:24 UTC (Tue) by developer122 (guest, #152928)
In reply to: Stuffing the return stack buffer by izbyshev
Parent article: Stuffing the return stack buffer

In other words, "it's fixed until we discover otherwise"

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Stuffing the return stack buffer

Posted Jul 26, 2022 13:47 UTC (Tue) by mss (subscriber, #138799) [Link] (1 responses)

Some knowledgeable people already say that:

Retpoline is not safe on Skylake-era CPUs, and we knew this before the Spectre/Meltdown embargo broke in Jan '18.

RSB stuffing relies on retpolines for Spectre v2 mitigation.

Stuffing the return stack buffer

Posted Jul 26, 2022 14:47 UTC (Tue) by izbyshev (subscriber, #107996) [Link]

> RSB stuffing relies on retpolines for Spectre v2 mitigation.

FWIW, it's vice versa: retpolines rely on RSB stuffing to make them less broken on Skylake.

But yeah, the general sentiment of that email is that apparently retpolines would be unsafe on Skylake even if RSB stuffing were added in all cases when the RSB might become empty.