linux-kernel - Re: [PATCH RESEND] KVM: X86: Fix stack-out-of-bounds read in write

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Message-ID: <e9adc7ef-37c5-d2e0-ce3d-1aa70c3432f1@redhat.com>
Date:   Tue, 12 Dec 2017 17:07:54 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH RESEND] KVM: X86: Fix stack-out-of-bounds read in
 write_mmio

On 12/12/2017 09:57, Wanpeng Li wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bc5d853..51e7932 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4690,7 +4690,10 @@ static int write_emulate(struct kvm_vcpu *vcpu, gpa_t gpa,
>  
>  static int write_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes, void *val)
>  {
> -	trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, *(u64 *)val);
> +	u64 data = 0;
> +
> +	memcpy(&data, val, min(8, bytes));
> +	trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, data);
>  	return vcpu_mmio_write(vcpu, gpa, bytes, val);
>  }
>  
> 

Please do the memcpy in TRACE_EVENT(kvm_mmio)'s TP_fast_assign block.
That is done only when the trace event is active.

Thanks,

Paolo