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Re: kvm: using uninitialized var in tdp_page_fault

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  Re: kvm: using uninitialized var in tdp_page_fault Paolo Bonzini <pbonzini@redhat.com> - 2016-02-23 15:40 +0100
    Re: kvm: using uninitialized var in tdp_page_fault Dmitry Vyukov <dvyukov@google.com> - 2016-02-28 14:10 +0100

#1340707 — Re: kvm: using uninitialized var in tdp_page_fault

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

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#1345242

On Tue, Feb 23, 2016 at 3:30 PM, Paolo Bonzini <pbonzini@redhat.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.

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