Re: [PATCH v4 0/4] KVM: x86: Fix and harden reg caching from !TASK context

[Paolo Bonzini]

On Thu, Oct 10, 2024 at 6:17 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Thu, Oct 10, 2024, Paolo Bonzini wrote:
> > On 10/9/24 19:49, Sean Christopherson wrote:
> > > Fix a (VMX only) bug reported by Maxim where KVM caches a stale SS.AR_BYTES
> > > when involuntary preemption schedules out a vCPU during vmx_vcpu_rest(), and
> > > ultimately clobbers the VMCS's SS.AR_BYTES if userspace does KVM_GET_SREGS
> > > => KVM_SET_SREGS, i.e. if userspace writes the stale value back into KVM.
> > >
> > > v4, as this is a spiritual successor to Maxim's earlier series.
> > >
> > > Patch 1 fixes the underlying problem by avoiding the cache in kvm_sched_out().
> >
> > I think we want this one in stable?
>
> If anything, we should send Maxim's patch to stable trees.  While not a complete
> fix, it resolves the only known scenario where caching SS.AR_BYTES is truly
> problematic, it's as low risk as patches get, and it's much more likely to backport
> cleanly to older kernels.

Ok, this works for me.

Paolo