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

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@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/

---

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