linux-kernel - Re: kvm: using uninitialized var in tdp_page

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Date:	Sun, 28 Feb 2016 14:08:14 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Gleb Natapov <gleb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>
Subject: Re: kvm: using uninitialized var in tdp_page_fault

On Tue, Feb 23, 2016 at 3:30 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
>
> 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)) {



Sasha, does it fix the issue? This patch is still not merged.