Re: [PATCH v1 08/11] KVM: arm64: Add host and hypervisor vCPU lookup primitives

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] flush_hyp_vcpu() incorrectly copies MDCR_EL2 from the untrusted host context for protected VMs, violating EL2 security guidelines.
--

commit 11498ed516d4ebc65b4ad00086974239ee0e2eb4
Author: Marc Zyngier <maz@kernel.org>
KVM: arm64: Add host and hypervisor vCPU lookup primitives

This commit introduces primitives to translate a host vCPU into the
hypervisor's address space. It refactors handle___kvm_vcpu_run() to use
these new lookup primitives.

> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
[ ... ]
> @@ -214,23 +245,16 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
>  			goto out;
>  		}
>  
> -		if (!hyp_vcpu) {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -
>  		flush_hyp_vcpu(hyp_vcpu);

[Severity: High]
This is a pre-existing issue, but does flush_hyp_vcpu() incorrectly copy
mdcr_el2 from the untrusted host context for protected VMs?

Looking at flush_hyp_vcpu() in arch/arm64/kvm/hyp/nvhe/hyp-main.c:

static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
{
        struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu;
        [ ... ]
        hyp_vcpu->vcpu.arch.mdcr_el2 = host_vcpu->arch.mdcr_el2;
        [ ... ]
}

According to the pKVM EL2 Security and Trust Boundary guidelines, trap
configuration registers like mdcr_el2 must be initialized in an EL2-private
context for protected VMs. They must not rely on values written by the host.

Because host_vcpu resides in untrusted host memory, this unconditional
assignment could allow a compromised host to overwrite the mdcr_el2
configuration of a protected VM. This could potentially allow the host to
manipulate guest debug exceptions and break guest confidentiality or
hypervisor isolation.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260612065925.755562-1-tabba@google.com?part=8