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Subject[PATCH 5.10 077/120] Fix unsynchronized access to sev members through svm_register_enc_region
Date
From: Peter Gonda <pgonda@google.com>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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/sev.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -320,6 +320,8 @@ static struct page **sev_pin_memory(stru
unsigned long first, last;
int ret;

+ lockdep_assert_held(&kvm->lock);
+
if (ulen == 0 || uaddr + ulen < uaddr)
return ERR_PTR(-EINVAL);

@@ -1001,12 +1003,20 @@ int svm_register_enc_region(struct 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
@@ -1015,13 +1025,6 @@ int svm_register_enc_region(struct 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:

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