Messages in this thread | | | Subject | Re: [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS | From | "Xu, Like" <> | Date | Mon, 25 Jan 2021 20:07:06 +0800 |
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On 2021/1/25 19:13, Peter Zijlstra wrote: > On Mon, Jan 25, 2021 at 04:08:22PM +0800, Like Xu wrote: >> Hi Peter, >> >> On 2021/1/22 17:56, Peter Zijlstra wrote: >>> On Fri, Jan 15, 2021 at 10:51:38AM -0800, Sean Christopherson wrote: >>>> On Fri, Jan 15, 2021, Andi Kleen wrote: >>>>>> I'm asking about ucode/hardare. Is the "guest pebs buffer write -> PEBS PMI" >>>>>> guaranteed to be atomic? >>>>> Of course not. >>>> So there's still a window where the guest could observe the bad counter index, >>>> correct? >>> Guest could do a hypercall to fix up the DS area before it tries to read >>> it I suppose. Or the HV could expose the index mapping and have the >>> guest fix up it. >> A weird (malicious) guest would read unmodified PEBS records in the >> guest PEBS buffer from other vCPUs without the need for hypercall or >> index mapping from HV. >> >> Do you see any security issues on this host index leak window? >> >>> Adding a little virt crud on top shouldn't be too hard. >>> >> The patches 13-17 in this version has modified the guest PEBS buffer >> to correct the index mapping information in the guest PEBS records. > Right, but given there is no atomicity between writing the DS area and > triggering the PMI (as already established earlier in this thread), a > malicious guest can already access this information, no? >
So under the premise that counter cross-mapping is allowed, how can hypercall help fix it ?
Personally, I think it is acceptable at the moment, and no security issues based on this have been defined and found.
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