linux-kernel - Re: [PATCH v2 8/8] KVM: x86: Bug the VM on an out-of-bounds data read

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Message-ID: <87ilpkok0h.fsf@redhat.com>
Date:   Wed, 01 Jun 2022 10:39:10 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Robert Dinse <nanook@...imo.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 8/8] KVM: x86: Bug the VM on an out-of-bounds data read

Sean Christopherson <seanjc@...gle.com> writes:

> Bug the VM and terminate emulation if an out-of-bounds read into the
> emulator's data cache occurs.  Knowingly contuining on all but guarantees
> that KVM will overwrite random kernel data, which is far, far worse than
> killing the VM.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/emulate.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 2aa17462a9ac..39ea9138224c 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -1373,7 +1373,8 @@ static int read_emulated(struct x86_emulate_ctxt *ctxt,
>  	if (mc->pos < mc->end)
>  		goto read_cached;
>  
> -	WARN_ON((mc->end + size) >= sizeof(mc->data));
> +	if (KVM_EMULATOR_BUG_ON((mc->end + size) >= sizeof(mc->data), ctxt))
> +		return X86EMUL_UNHANDLEABLE;
>  
>  	rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, size,
>  				      &ctxt->exception);

The last WARN_ON() is gone, cool)

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly