Messages in this thread | | | Subject | Re: [PATCH 0/5] Introduce support for PSF mitigation | From | "Saripalli, RK" <> | Date | Fri, 9 Apr 2021 11:50:16 -0500 |
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Josh, PSF being new, may be in the future someone will find something new.
This is really extra precaution.
On 4/9/2021 11:45 AM, Josh Poimboeuf wrote: > On Thu, Apr 08, 2021 at 09:56:47AM -0500, Saripalli, RK wrote: >> Josh, thank you for taking the time to review the patches. >> >> On 4/7/2021 5:39 PM, Josh Poimboeuf wrote: >>> On Tue, Apr 06, 2021 at 10:49:59AM -0500, Ramakrishna Saripalli wrote: >>>> Because PSF speculation is limited to the current program context, >>>> the impact of bad PSF speculation is very similar to that of >>>> Speculative Store Bypass (Spectre v4) >>>> >>>> Predictive Store Forwarding controls: >>>> There are two hardware control bits which influence the PSF feature: >>>> - MSR 48h bit 2 – Speculative Store Bypass (SSBD) >>>> - MSR 48h bit 7 – Predictive Store Forwarding Disable (PSFD) >>>> >>>> The PSF feature is disabled if either of these bits are set. These bits >>>> are controllable on a per-thread basis in an SMT system. By default, both >>>> SSBD and PSFD are 0 meaning that the speculation features are enabled. >>>> >>>> While the SSBD bit disables PSF and speculative store bypass, PSFD only >>>> disables PSF. >>>> >>>> PSFD may be desirable for software which is concerned with the >>>> speculative behavior of PSF but desires a smaller performance impact than >>>> setting SSBD. >>> >>> Hi Ramakrishna, >>> >>> Is there a realistic scenario where an application would want to disable >>> PSF, but not disable SSB? >> >> It is possible most applications have been reviewed and scrubbed for >> SSB-type attacks but PSF-type issues may not have been looked at yet. > > It's "possible", but is it realistic? As far as I know, SSB is > impractical to scrub an application for. > > Do we know of any real-world cases where this option is needed? >
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