Commit f1ecde00 authored Jan 27, 2021 by Peter Gonda Committed by Greg Kroah-Hartman Feb 13, 2021

Fix unsynchronized access to sev members through svm_register_enc_region



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: 1e80fdc0 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 050462f0

arch/x86/kvm/svm.c

+11 −7

Original line number	Diff line number	Diff line
		@@ -1832,6 +1832,8 @@ 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;

		@@ -7084,12 +7086,21 @@ 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
		@@ -7098,13 +7109,6 @@ 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: