[PATCH] Fix unsynchronized access to sev members through svm_register_enc_region

[Peter Gonda]

sev_pin_memory assumes that callers hold the kvm->lock. This was true for
all callers except svm_register_enc_region since it does not originate
from svm_mem_enc_op. Also added lockdep annotation to help prevent
future regressions.

Tested: Booted SEV enabled VM on host.

Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Joerg Roedel <j...@8bytes.org>
Cc: Tom Lendacky <thomas.lenda...@amd.com>
Cc: Brijesh Singh <brijesh.si...@amd.com>
Cc: Sean Christopherson <sea...@google.com>
Cc: x...@kernel.org
Cc: k...@vger.kernel.org
Cc: sta...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Fixes: 116a2214c5173 (KVM: SVM: Pin guest memory when SEV is active)
Signed-off-by: Peter Gonda <pgo...@google.com>

---
 arch/x86/kvm/svm.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index afdc5b44fe9f..9884e57f3d0f 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1699,6 +1699,8 @@ 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;
 
@@ -7228,12 +7230,19 @@ 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;
                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
@@ -7242,13 +7251,6 @@ 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:
-- 
2.30.0.280.ga3ce27912f-goog