linux-kernel - Re: [PATCH 1/5] KVM: x86: Emulator does not calculate address correctly

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Message-ID: <536A3BD7.10804@redhat.com>
Date:	Wed, 07 May 2014 15:57:43 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>, mtosatti@...hat.com,
	hpa@...or.com
CC:	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] KVM: x86: Emulator does not calculate address correctly

Il 07/05/2014 14:32, Nadav Amit ha scritto:
> In long-mode, when the address size is 4 bytes, the linear address is not
> truncated as the emulator mistakenly does.  Instead, the offset within the
> segment (the ea field) should be truncated according to the address size.
>
> As Intel SDM says: "In 64-bit mode, the effective address components are added
> and the effective address is truncated ... before adding the full 64-bit
> segment base."
>
> Signed-off-by: Nadav Amit <namit@...technion.ac.il>
> ---
>  arch/x86/kvm/emulate.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index e8a5840..743e8e3 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -631,7 +631,8 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
>  	u16 sel;
>  	unsigned cpl;
>
> -	la = seg_base(ctxt, addr.seg) + addr.ea;
> +	la = seg_base(ctxt, addr.seg) +
> +	    (ctxt->ad_bytes == 8 ? addr.ea : (u32)addr.ea);

I think you need "fetch || ctxt->ad_bytes == 8" here.

Paolo

>  	switch (ctxt->mode) {
>  	case X86EMUL_MODE_PROT64:
>  		if (((signed long)la << 16) >> 16 != la)
> @@ -678,7 +679,7 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
>  		}
>  		break;
>  	}
> -	if (fetch ? ctxt->mode != X86EMUL_MODE_PROT64 : ctxt->ad_bytes != 8)
> +	if (ctxt->mode != X86EMUL_MODE_PROT64)
>  		la &= (u32)-1;
>  	if (insn_aligned(ctxt, size) && ((la & (size - 1)) != 0))
>  		return emulate_gp(ctxt, 0);
>

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