[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/domctl: Adjust size calculations for XEN_DOMCTL_get{_ext_vcpucontext, vcpuextstate}
>>> On 28.04.14 at 12:59, <andrew.cooper3@xxxxxxxxxx> wrote: > On 28/04/14 11:34, Jan Beulich wrote: >>>>> On 28.04.14 at 11:43, <andrew.cooper3@xxxxxxxxxx> wrote: >>> XEN_DOMCTL_get_ext_vcpucontext suffers from the same issue but while trying >>> to >>> fix that in similar way, I discovered that it had a genuine bug when >>> returning >>> the count of MSRs to the toolstack. When running the hypercall on an active >>> vcpu, the vcpu can arbitrarily alter the count returned to the toolstack by >>> clearing and setting relevant MSRs. >> Did you perhaps overlook the vcpu_pause() there? > > There is a vcpu pause in the hypercall, so for the duration of the > hypercall the returned value will be consistent. > > However without the toolstack pausing the domain, issuing this hypercall > twice, first to get the size and second to get the data might still > result in -ENOBUFS if the vcpu suddenly writes non-0 values to the MSRs. And in what way is this different from e.g. XEN_DOMCTL_get_vcpuextstate? >> I'm also not really in favor of forcing the tools to allocate memory >> for the array if in fact no MSRs are being used by the guest. > > If there are no msrs to receive, then passing a NULL guest handle is > still fine. But the caller can't know whether the count was non-zero just because that's the theoretical maximum or because some MSR really is in use. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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