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 [email protected]

Signed-off-by Tom Roeder <[email protected]>

---
Changelog since v1:
- Changed the copy_to_user calls in vmx_get_nested_state to copy the full 4k buffer.

 arch/x86/kvm/vmx/nested.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

arch/x86/kvm/vmx/nested.c +7 -3

index 2616bd2c7f2c7..ce81539238547 100644
@@ -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))