Re: [PATCH V2] Fix unsynchronized access to sev members through svm_register_enc_region

[Paolo Bonzini]

On 27/01/21 17:15, Peter Gonda wrote:
> Grab kvm->lock before pinning memory when registering an encrypted
> region; sev_pin_memory() relies on kvm->lock being held to ensure
> correctness when checking and updating the number of pinned pages.
>
> Add a lockdep assertion to help prevent future regressions.
>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Joerg Roedel <joro@xxxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Fixes: 1e80fdc09d12 ("KVM: SVM: Pin guest memory when SEV is active")
> Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
>
> V2
>   - Fix up patch description
>   - Correct file paths svm.c -> sev.c
>   - Add unlock of kvm->lock on sev_pin_memory error
>
> V1
>   - https://lore.kernel.org/kvm/20210126185431.1824530-1-pgonda@xxxxxxxxxx/
>
> ---
>   arch/x86/kvm/svm/sev.c | 17 ++++++++++-------
>   1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c8ffdbc81709..b80e9bf0a31b 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -342,6 +342,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
>   	unsigned long first, last;
>   	int ret;
>   
> +	lockdep_assert_held(&kvm->lock);
> +
>   	if (ulen == 0 || uaddr + ulen < uaddr)
>   		return ERR_PTR(-EINVAL);
>   
> @@ -1119,12 +1121,20 @@ int svm_register_enc_region(struct kvm *kvm,
>   	if (!region)
>   		return -ENOMEM;
>   
> +	mutex_lock(&kvm->lock);
>   	region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages, 1);
>   	if (IS_ERR(region->pages)) {
>   		ret = PTR_ERR(region->pages);
> +		mutex_unlock(&kvm->lock);
>   		goto e_free;
>   	}
>   
> +	region->uaddr = range->addr;
> +	region->size = range->size;
> +
> +	list_add_tail(&region->list, &sev->regions_list);
> +	mutex_unlock(&kvm->lock);
> +
>   	/*
>   	 * The guest may change the memory encryption attribute from C=0 -> C=1
>   	 * or vice versa for this memory range. Lets make sure caches are
> @@ -1133,13 +1143,6 @@ int svm_register_enc_region(struct kvm *kvm,
>   	 */
>   	sev_clflush_pages(region->pages, region->npages);
>   
> -	region->uaddr = range->addr;
> -	region->size = range->size;
> -
> -	mutex_lock(&kvm->lock);
> -	list_add_tail(&region->list, &sev->regions_list);
> -	mutex_unlock(&kvm->lock);
> -
>   	return ret;
>   
>   e_free:

Queued, thanks.

Paolo