Messages in this thread |  | | From | "Singh, Balbir" <> | Subject | Re: [RFC PATCH v2 0/4] arch/x86: Optionally flush L1D on context switch | Date | Mon, 30 Mar 2020 01:13:46 +0000 |
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On Wed, 2020-03-25 at 18:10 +1100, Balbir Singh wrote: > This patch is a continuation of RFC/PoC to start the discussion on > optionally > flushing L1D cache. The goal is to allow tasks that are paranoid due to the > recent snoop assisted data sampling vulnerabilites, to flush their L1D on > being > switched out. This protects their data from being snooped or leaked via > side channels after the task has context switched out. > > The points of discussion/review are (with updates): > > 1. Discuss the use case and the right approach to address this > A. Generally there seems to be consensus that we need this > > 2. Does an arch prctl allowing for opt-in flushing make sense, would other > arches care about something similar? > A. We definitely build this for x86, have not heard from any other arch > maintainers. There was suggestion to make this a prctl and let each > arch implement L1D flushing if needed, there is no arch agnostic > software L1D flush. > > 3. There is a fallback software L1D load, similar to what L1TF does, but > we don't prefetch the TLB, is that sufficient? > A. There was no conclusion, I suspect we don't need this > > 4. Should we consider cleaning up the L1D on arrival of tasks? > A. For now, we think this case is not the priority for this patchset. > > In summary, this is an early PoC to start the discussion on the need for > conditional L1D flushing based on the security posture of the > application and the sensitivity of the data it has access to or might > have access to. > > Changelog v2: > - Reuse existing code for allocation and flush > - Simplify the goto logic in the actual l1d_flush function > - Optimize the code path with jump labels/static functions > > Cc: keescook@chromium.org > > Balbir Singh (4): > arch/x86/kvm: Refactor l1d flush lifecycle management > arch/x86: Refactor tlbflush and l1d flush > arch/x86: Optionally flush L1D on context switch > arch/x86: L1D flush, optimize the context switch >
Ping, looking for comments and criticism of the approach. I understand with the merge window around the corner everyone is busy. There is a bug in the v2 RFC series, I am happy to post a version without the RFC for broader testing and feedback.
I am quite keen to hear about the interface and any concerns with the arch_prctl() interface.
Balbir Singh.
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