[PATCH 5/5] KVM: arm64: Disable privileged hypercalls after pKVM finalisation

[Marc Zyngier]

On Thu, 23 Sep 2021 14:02:11 +0100,
Will Deacon <will at kernel.org> wrote:
> 
> On Thu, Sep 23, 2021 at 01:56:21PM +0100, Marc Zyngier wrote:
> > On Thu, 23 Sep 2021 12:22:56 +0100,
> > Will Deacon <will at kernel.org> wrote:

[...]

> > >  static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
> > >  {
> > >  	DECLARE_REG(unsigned long, id, host_ctxt, 0);
> > > +	unsigned long hcall_min = 0;
> > >  	hcall_t hfn;
> > >  
> > > +	if (static_branch_unlikely(&kvm_protected_mode_initialized))
> > > +		hcall_min = __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize;
> > > +
> > >  	id -= KVM_HOST_SMCCC_ID(0);
> > >  
> > > -	if (unlikely(id >= ARRAY_SIZE(host_hcall)))
> > > +	if (unlikely(id < hcall_min || id >= ARRAY_SIZE(host_hcall)))
> > 
> > So I can still issue a pkvm_prot_finalize after finalisation? Seems
> > odd. As hcall_min has to be inclusive, you probably want it to be set
> > to __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp once protected.
> 
> Yeah, I ended up addresing that one in the previous patch. The problem is
> that we need to allow pkvm_prot_finalize to be called on each CPU, so I
> think we'd end up having an extra "really finalize damnit!" call to be
> issued _once_ after each CPU is done with the finalisation if we want
> to lock it down.
> 
> The approach I took instead is to make pkvm_prot_finalize return -EBUSY
> if it's called on a CPU where it's already been called.

Ah, I see. Serves me right for reading patches out of order. Finalise
is of course per-CPU, and the static key global. Epic fail.

Probably deserves a comment, because I'm surely going to jump at that
again in three months.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.