kvm: x86/vmx: Use kzalloc for cached_vmcs12

This changes the allocation of cached_vmcs12 to use kzalloc instead of
kmalloc. This removes the information leak found by Syzkaller (see
Reported-by) in this case and prevents similar leaks from happening
based on cached_vmcs12.

It also changes vmx_get_nested_state to copy out the full 4k VMCS12_SIZE
in copy_to_user rather than only the size of the struct.

Tested: rebuilt against head, booted, and ran the syszkaller repro
  https://syzkaller.appspot.com/text?tag=ReproC&x=174efca3400000 without
  observing any problems.

Reported-by: syzbot+ded1696f6b50b615b630@syzkaller.appspotmail.com
Fixes: 1877921b6206427f6676139c30ed44fc07e5d8f9
Cc: stable@vger.kernel.org
Signed-off-by: Tom Roeder <tmroeder@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 2616bd2c7f2c78b25339eff719d37a22b9070404..ce81539238547bb7e1d9f40d9ff4d198c2343f2c 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4140,11 +4140,11 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
        if (r < 0)
                goto out_vmcs02;
 
-       vmx->nested.cached_vmcs12 = kmalloc(VMCS12_SIZE, GFP_KERNEL);
+       vmx->nested.cached_vmcs12 = kzalloc(VMCS12_SIZE, GFP_KERNEL);
        if (!vmx->nested.cached_vmcs12)
                goto out_cached_vmcs12;
 
-       vmx->nested.cached_shadow_vmcs12 = kmalloc(VMCS12_SIZE, GFP_KERNEL);
+       vmx->nested.cached_shadow_vmcs12 = kzalloc(VMCS12_SIZE, GFP_KERNEL);
        if (!vmx->nested.cached_shadow_vmcs12)
                goto out_cached_shadow_vmcs12;
 
@@ -5263,13 +5263,17 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
                        copy_shadow_to_vmcs12(vmx);
        }
 
-       if (copy_to_user(user_kvm_nested_state->data, vmcs12, sizeof(*vmcs12)))
+       /*
+        * Copy over the full allocated size of vmcs12 rather than just the size
+        * of the struct.
+        */
+       if (copy_to_user(user_kvm_nested_state->data, vmcs12, VMCS12_SIZE))
                return -EFAULT;
 
        if (nested_cpu_has_shadow_vmcs(vmcs12) &&
            vmcs12->vmcs_link_pointer != -1ull) {
                if (copy_to_user(user_kvm_nested_state->data + VMCS12_SIZE,
-                                get_shadow_vmcs12(vcpu), sizeof(*vmcs12)))
+                                get_shadow_vmcs12(vcpu), VMCS12_SIZE))
                        return -EFAULT;
        }