[PATCH v1 3/3] KVM: arm64: Create each pKVM hyp vcpu after its corresponding host vcpu
Will Deacon
will at kernel.org
Mon Feb 17 07:30:31 PST 2025
On Fri, Feb 14, 2025 at 03:02:58PM +0000, Fuad Tabba wrote:
> Instead of creating and initializing _all_ hyp vcpus in pKVM when
> the first host vcpu runs for the first time, initialize _each_
> hyp vcpu in conjunction with its corresponding host vcpu.
>
> Some of the host vcpu state (e.g., system registers and traps
> values) are not initialized until the first time the host vcpu is
> run. Therefore, initializing a hyp vcpu before its corresponding
> host vcpu has run for the first time might not view the complete
> host state of these vcpus.
>
> Additionally, this behavior is inline with non-protected modes.
>
> Signed-off-by: Fuad Tabba <tabba at google.com>
> ---
> arch/arm64/include/asm/kvm_host.h | 2 +
> arch/arm64/include/asm/kvm_pkvm.h | 1 +
> arch/arm64/kvm/arm.c | 4 ++
> arch/arm64/kvm/hyp/include/nvhe/pkvm.h | 6 ---
> arch/arm64/kvm/hyp/nvhe/pkvm.c | 54 +++++++++++++++-----------
> arch/arm64/kvm/pkvm.c | 28 ++++++-------
> 6 files changed, 53 insertions(+), 42 deletions(-)
[...]
> static int init_pkvm_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu,
> struct pkvm_hyp_vm *hyp_vm,
> - struct kvm_vcpu *host_vcpu,
> - unsigned int vcpu_idx)
> + struct kvm_vcpu *host_vcpu)
> {
> int ret = 0;
>
> if (hyp_pin_shared_mem(host_vcpu, host_vcpu + 1))
> return -EBUSY;
>
> - if (host_vcpu->vcpu_idx != vcpu_idx) {
> - ret = -EINVAL;
> - goto done;
> - }
> -
> hyp_vcpu->host_vcpu = host_vcpu;
>
> hyp_vcpu->vcpu.kvm = &hyp_vm->kvm;
> hyp_vcpu->vcpu.vcpu_id = READ_ONCE(host_vcpu->vcpu_id);
> - hyp_vcpu->vcpu.vcpu_idx = vcpu_idx;
> + hyp_vcpu->vcpu.vcpu_idx = READ_ONCE(host_vcpu->vcpu_idx);
>
> hyp_vcpu->vcpu.arch.hw_mmu = &hyp_vm->kvm.arch.mmu;
> hyp_vcpu->vcpu.arch.cflags = READ_ONCE(host_vcpu->arch.cflags);
> @@ -687,27 +689,28 @@ int __pkvm_init_vcpu(pkvm_handle_t handle, struct kvm_vcpu *host_vcpu,
> goto unlock;
> }
>
> - idx = hyp_vm->nr_vcpus;
> + ret = init_pkvm_hyp_vcpu(hyp_vcpu, hyp_vm, host_vcpu);
> + if (ret)
> + goto unlock;
> +
> + idx = hyp_vcpu->vcpu.vcpu_idx;
> if (idx >= hyp_vm->kvm.created_vcpus) {
> ret = -EINVAL;
> goto unlock;
> }
>
> - ret = init_pkvm_hyp_vcpu(hyp_vcpu, hyp_vm, host_vcpu, idx);
> - if (ret)
> + if (hyp_vm->vcpus[idx]) {
> + ret = -EINVAL;
> goto unlock;
> + }
I'm not sure how much we care at EL2, but it looks like there's a
potential spectre gadget here given that 'idx' is now untrusted.
Perhaps chuck something like:
idx = array_index_nospec(idx, hyp_vm->kvm.created_vcpus);
before indexing into 'hyp_vm->vcpus[]'?
Either way:
Acked-by: Will Deacon <will at kernel.org>
Will
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