Re: kvm: using uninitialized var in tdp_page_fault

[Paolo Bonzini <pbonzini@redhat.com>]

On 15/01/2016 18:02, Sasha Levin wrote:
> Hi all,
> 
> While fuzzing with syzkaller on the latest -next kernel running on a KVM tools
> guest, I've hit the following use of an uninitialized variable:
> 
> [  810.783676] UBSAN: Undefined behaviour in arch/x86/kvm/mmu.c:3502:6
> 
> [  810.785650] load of value 179 is not a valid value for type '_Bool'

Can you check this patch:

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index be3cef12706c..fd54613a1204 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1449,8 +1449,11 @@ pfn_t __gfn_to_pfn_memslot(struct
 	if (addr == KVM_HVA_ERR_RO_BAD)
 		return KVM_PFN_ERR_RO_FAULT;
 
-	if (kvm_is_error_hva(addr))
+	if (kvm_is_error_hva(addr)) {
+		if (writable)
+			*writable = false;
 		return KVM_PFN_NOSLOT;
+	}
 
 	/* Do not map writable pfn in the readonly memslot. */
 	if (writable && memslot_is_readonly(slot)) {

Thanks,

Paolo