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SubjectRe: [PATCH for 5.4] Fix unsynchronized access to sev members through svm_register_enc_region
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On 08/02/21 17:48, Peter Gonda wrote:
> commit 19a23da53932bc8011220bd8c410cb76012de004 upstream.
>
> 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@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: stable@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Fixes: 1e80fdc09d12 ("KVM: SVM: Pin guest memory when SEV is active")
> Signed-off-by: Peter Gonda <pgonda@google.com>
>
> 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@google.com/
>
> Message-Id: <20210127161524.2832400-1-pgonda@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/svm.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2b506904be02..93c89f1ffc5d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1830,6 +1830,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
> struct page **pages;
> unsigned long first, last;
>
> + lockdep_assert_held(&kvm->lock);
> +
> if (ulen == 0 || uaddr + ulen < uaddr)
> return NULL;
>
> @@ -7086,12 +7088,21 @@ static 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 (!region->pages) {
> ret = -ENOMEM;
> + mutex_unlock(&kvm->lock);
> goto e_free;
> }
>
> + region->uaddr = range->addr;
> + region->size = range->size;
> +
> + mutex_lock(&kvm->lock);
> + 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
> @@ -7100,13 +7111,6 @@ static 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:
>

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

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