From: Peter Gonda <pgonda@google.com>
Date: Wed, 27 Jan 2021 08:15:24 -0800
Subject: Fix unsynchronized access to sev members through
 svm_register_enc_region
Git-commit: 19a23da53932bc8011220bd8c410cb76012de004
Patch-mainline: v5.11-rc7
References: bsc#1114648

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>
Acked-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kvm/svm.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1791,6 +1791,8 @@ static struct page **sev_pin_memory(stru
 	struct page **pages;
 	int first, last;
 
+	lockdep_assert_held(&kvm->lock);
+
 	/* Calculate number of pages. */
 	first = (uaddr & PAGE_MASK) >> PAGE_SHIFT;
 	last = ((uaddr + ulen - 1) & PAGE_MASK) >> PAGE_SHIFT;
@@ -7019,12 +7021,20 @@ static int svm_register_enc_region(struc
 	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;
+
+	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
@@ -7033,13 +7043,6 @@ static int svm_register_enc_region(struc
 	 */
 	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: