Re: [PATCH v2 01/14] KVM: SVM: Zero out the VMCB array used to track SEV ASID association

Brijesh Singh
2021-01-14T20:58:56Z

On 1/13/21 6:36 PM, Sean Christopherson wrote:
> Zero out the array of VMCB pointers so that pre_sev_run() won't see
> garbage when querying the array to detect when an SEV ASID is being
> associated with a new VMCB. In practice, reading random values is all
> but guaranteed to be benign as a false negative (which is extremely
> unlikely on its own) can only happen on CPU0 on the first VMRUN and would
> only cause KVM to skip the ASID flush. For anything bad to happen, a
> previous instance of KVM would have to exit without flushing the ASID,
> _and_ KVM would have to not flush the ASID at any time while building the
> new SEV guest.
>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Fixes: 70cd94e60c73 ("KVM: SVM: VMRUN should use associated ASID when SEV is enabled")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/svm/svm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 7ef171790d02..ccf52c5531fb 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -573,7 +573,7 @@ static int svm_cpu_init(int cpu)
> if (svm_sev_enabled()) {
> sd->sev_vmcbs = kmalloc_array(max_sev_asid + 1,
> sizeof(void *),
> - GFP_KERNEL);
> + GFP_KERNEL | __GFP_ZERO);
> if (!sd->sev_vmcbs)
> goto free_save_area;
> }

Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>