Re: [PATCH v15 21/23] KVM: selftests: Add support for per-VM ucall ops on x86

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] kvm: selftests: host-side ucall_x86_ops is a process-wide global, breaking multi-VM isolation
--

commit abf66b381d3f3c93b178cddc07865810aae03f24
Author: Sean Christopherson <seanjc@google.com>

KVM: selftests: Add support for per-VM ucall ops on x86

This commit introduces a layer of indirection for x86 ucall operations to
support TDX VMs. It replaces hardcoded ucall functions with an operations
structure that can be customized.

> diff --git a/tools/testing/selftests/kvm/lib/x86/ucall.c b/tools/testing/selftests/kvm/lib/x86/ucall.c
> index 38050c60a0670..c003df3c7b8a8 100644
> --- a/tools/testing/selftests/kvm/lib/x86/ucall.c
> +++ b/tools/testing/selftests/kvm/lib/x86/ucall.c

[ ... ]

> @@ -26,3 +26,26 @@ void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
>  	}
>  	return NULL;
>  }
> +
> +static struct {
> +	void (*do_ucall)(gva_t uc);
> +	void *(*get_ucall)(struct kvm_vcpu *vcpu);
> +} ucall_x86_ops = {
> +	.do_ucall = ucall_x86_do_ucall,
> +	.get_ucall = ucall_x86_get_ucall,
> +};

[Severity: Medium]
The commit message mentions adding support for per-VM ucall ops, but
ucall_x86_ops is defined as a static global variable. Doesn't this mean it
will act as a process-wide shared variable on the host side, rather than
being isolated per-VM?

If a selftest process initializes a TDX VM (which presumably overrides
these operations) followed by a non-TDX VM, or runs multiple VMs
concurrently, will the non-TDX VMs incorrectly end up using the TDX ucall
callbacks?

> +
> +void ucall_arch_init(struct kvm_vm *vm, gpa_t mmio_gpa)
> +{
> +	sync_global_to_guest(vm, ucall_x86_ops);
> +}
> +
> +void ucall_arch_do_ucall(gva_t uc)
> +{
> +	return ucall_x86_ops.do_ucall(uc);
> +}
> +
> +void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
> +{
> +	return ucall_x86_ops.get_ucall(vcpu);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261001-tdx-selftests-v15-0-7c62a5d8a992@google.com?part=21