Re: [PATCH RFC v7 10/64] KVM: SEV: Populate private memory fd during LAUNCH_UPDATE_DATA

[Michael Roth <michael.roth@amd.com>]

On Fri, Jan 13, 2023 at 08:11:14PM +0100, Borislav Petkov wrote:
> On Wed, Dec 14, 2022 at 01:40:02PM -0600, Michael Roth wrote:
> > From: Vishal Annapurve <vannapurve@google.com>
> > 
> > This change adds handling of HVA ranges to copy contents
> 
> s/This change adds handling of/Handle/
> 
> > +static int sev_launch_update_priv_gfn_handler(struct kvm *kvm,
> > +					      struct kvm_gfn_range *range,
> > +					      struct kvm_sev_cmd *argp)
> > +{
> > +	struct sev_data_launch_update_data data;
> > +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > +	gfn_t gfn;
> > +	kvm_pfn_t pfn;
> > +	struct kvm_memory_slot *memslot = range->slot;
> > +	int ret = 0;
> > +
> > +	data.reserved = 0;
> > +	data.handle = sev->handle;
> > +
> > +	for (gfn = range->start; gfn < range->end; gfn++) {
> > +		int order;
> > +		void *kvaddr;
> > +
> > +		ret = kvm_restricted_mem_get_pfn(memslot, gfn, &pfn, &order);
> > +		if (ret)
> > +			return ret;
> > +
> > +		kvaddr = pfn_to_kaddr(pfn);
> > +		if (!virt_addr_valid(kvaddr)) {
> > +			pr_err("Invalid kvaddr 0x%llx\n", (uint64_t)kvaddr);
> 
> Is that some debugging help leftover or what is that printk issued for?

A mix of error-reporting and debugging I think. I think the error message
isn't needed since the error value will get plumbed straight to
userspace and anything beyond that is kernel debugging, so I added some
context and switched this to pr_debug().

> > +			ret = -EINVAL;
> > +			goto e_ret;
> > +		}
> > +
> > +		ret = kvm_read_guest_page(kvm, gfn, kvaddr, 0, PAGE_SIZE);
> > +		if (ret) {
> > +			pr_err("guest read failed 0x%x\n", ret);
> > +			goto e_ret;
> > +		}
> > +
> > +		if (!this_cpu_has(X86_FEATURE_SME_COHERENT))
> 
> check_for_deprecated_apis: WARNING: arch/x86/kvm/svm/sev.c:602: Do not use this_cpu_has() - use cpu_feature_enabled() instead.
> 
> > +			clflush_cache_range(kvaddr, PAGE_SIZE);
> > +
> > +		data.len = PAGE_SIZE;
> > +		data.address = __sme_set(pfn << PAGE_SHIFT);
> > +		ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_DATA, &data, &argp->error);
> > +		if (ret)
> > +			goto e_ret;
> > +		kvm_release_pfn_clean(pfn);
> > +	}
> > +	kvm_vm_set_region_attr(kvm, range->start, range->end,
> > +		true /* priv_attr */);
> 
> No need to break that line.
> 
> > +
> > +e_ret:
> > +	return ret;
> > +}
> > +
> > +static int sev_launch_update_gfn_handler(struct kvm *kvm, struct kvm_gfn_range *range,
> > +					 void *data)
> > +{
> > +	struct kvm_sev_cmd *argp = (struct kvm_sev_cmd *)data;
> > +
> > +	if (kvm_slot_can_be_private(range->slot))
> > +		return sev_launch_update_priv_gfn_handler(kvm, range, argp);
> > +
> > +	return sev_launch_update_shared_gfn_handler(kvm, range, argp);
> > +}
> > +
> > +static int sev_launch_update_data(struct kvm *kvm,
> > +		struct kvm_sev_cmd *argp)
> > +{
> > +	struct kvm_sev_launch_update_data params;
> > +
> > +	if (!sev_guest(kvm))
> > +		return -ENOTTY;
> > +
> > +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
> > +		return -EFAULT;
> 
> Not gonna check those user-supplied values for sanity?
> 
> Or is this check
> 
>         if (WARN_ON_ONCE(hva_end <= hva_start))
>                 return -EINVAL;
> 
> in kvm_vm_do_hva_range_op() enough?

Only partially, but kvm_vm_do_hva_range_op() should sanitize the address
range and only call sev_launch_update_gfn_handler() on valid GFNs within
the range, so if userspace provides a bogus HVA range that doesn't
actually correspond to a valid memslot it'll simply be treated as a
no-op.

-Mike

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette