[PATCH 4.20 079/117] kvm: x86/vmx: Use kzalloc for cached_vmcs12

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tom Roeder <tmroeder@xxxxxxxxxx>

commit 3a33d030daaa7c507e1c12d5adcf828248429593 upstream.

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 8fcc4b5923af5de58b80b53a069453b135693304
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Tom Roeder <tmroeder@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8315,11 +8315,11 @@ static int enter_vmx_operation(struct kv
 	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;
 
@@ -14853,13 +14853,17 @@ static int vmx_get_nested_state(struct k
 			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;
 	}