Re: [PATCH -tip] KVM: SVM: nested: Initialize on-stack pointers in svm_set_nested_state()

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Joerg Roedel <joro@8bytes.org> writes:

> From: Joerg Roedel <jroedel@suse.de>
>
> The save and ctl pointers need to be initialized to NULL because there
> is a way through the function in which there is no memory allocated
> for the pointers but where they are freed in the end.
>
> This involves the 'goto out_set_gif' before the memory for the
> pointers is allocated.
>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Fixes: 6ccbd29ade0d ("KVM: SVM: nested: Don't allocate VMCB structures on stack")
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  arch/x86/kvm/svm/nested.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 598a769f1961..72a3d6f87107 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1062,8 +1062,8 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>  	struct vmcb *hsave = svm->nested.hsave;
>  	struct vmcb __user *user_vmcb = (struct vmcb __user *)
>  		&user_kvm_nested_state->data.svm[0];
> -	struct vmcb_control_area *ctl;
> -	struct vmcb_save_area *save;
> +	struct vmcb_control_area *ctl = NULL;
> +	struct vmcb_save_area *save = NULL;
>  	int ret;
>  	u32 cr0;

Hi Joerg,

this was previously reported by Colin:
https://lore.kernel.org/kvm/20200911110730.24238-1-colin.king@canonical.com/

the fix itself looks good, however, I had an alternative suggestion on how
to fix this:
https://lore.kernel.org/kvm/87o8mclei1.fsf@vitty.brq.redhat.com/

-- 
Vitaly