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SubjectRe: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES_LIST ioctl
Hello Tom,

On Thu, Feb 04, 2021 at 10:14:37AM -0600, Tom Lendacky wrote:
> On 2/3/21 6:39 PM, Ashish Kalra wrote:
> > From: Brijesh Singh <brijesh.singh@amd.com>
> >
> > The ioctl is used to retrieve a guest's shared pages list.
> >
>
> ...
>
> > +int svm_get_shared_pages_list(struct kvm *kvm,
> > + struct kvm_shared_pages_list *list)
> > +{
> > + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > + struct shared_region_array_entry *array;
> > + struct shared_region *pos;
> > + int ret, nents = 0;
> > + unsigned long sz;
> > +
> > + if (!sev_guest(kvm))
> > + return -ENOTTY;
> > +
> > + if (!list->size)
> > + return -EINVAL;
> > +
> > + if (!sev->shared_pages_list_count)
> > + return put_user(0, list->pnents);
> > +
> > + sz = sev->shared_pages_list_count * sizeof(struct shared_region_array_entry);
> > + if (sz > list->size)
> > + return -E2BIG;
> > +
> > + array = kmalloc(sz, GFP_KERNEL);
> > + if (!array)
> > + return -ENOMEM;
> > +
> > + mutex_lock(&kvm->lock);
>
> I think this lock needs to be taken before the memory size is calculated. If
> the list is expanded after obtaining the size and before taking the lock,
> you will run off the end of the array.
>

Yes, as the page encryption status hcalls can happen simultaneously to
this ioctl, therefore this is an issue, so i will take the lock before
the memory size is calculated.

Thanks,
Ashish

>
> > + list_for_each_entry(pos, &sev->shared_pages_list, list) {
> > + array[nents].gfn_start = pos->gfn_start;
> > + array[nents++].gfn_end = pos->gfn_end;
> > + }
> > + mutex_unlock(&kvm->lock);
> > +
> > + ret = -EFAULT;
> > + if (copy_to_user(list->buffer, array, sz))
> > + goto out;
> > + if (put_user(nents, list->pnents))
> > + goto out;
> > + ret = 0;
> > +out:
> > + kfree(array);
> > + return ret;
> > +}
> > +

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