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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Joerg Roedel <joro@8bytes.org>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Joerg Roedel <jroedel@suse.de>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Borislav Petkov <bp@alien8.de>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Colin King <colin.king@canonical.com>
Subject: Re: [PATCH -tip] KVM: SVM: nested: Initialize on-stack pointers in svm_set_nested_state()
In-Reply-To: <20200914115129.10352-1-joro@8bytes.org>
References: <20200914115129.10352-1-joro@8bytes.org>
Date:   Mon, 14 Sep 2020 14:04:27 +0200
Message-ID: <87ft7klg38.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
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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