linux-kernel - Re: [PATCH 5/5] KVM: x86: Fix wrong masking on relative jump/call

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Date:	Wed, 07 May 2014 10:43:50 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>
Cc:	mtosatti@...hat.com, pbonzini@...hat.com, hpa@...or.com,
	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] KVM: x86: Fix wrong masking on relative jump/call

Nadav Amit <namit@...technion.ac.il> writes:

> Relative jumps and calls do the masking according to the operand size, and not
> according to the address size as the KVM emulator does today.  In 64-bit mode,
> the resulting RIP is always 64-bit. Otherwise it is masked according to the
> instruction operand-size. Note that when 16-bit address size is used, bits
> 63:32 are unmodified.
>
> Signed-off-by: Nadav Amit <namit@...technion.ac.il>
> ---
>  arch/x86/kvm/emulate.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 6833b41..e406705 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -506,7 +506,9 @@ static void rsp_increment(struct x86_emulate_ctxt *ctxt, int inc)
>  
>  static inline void jmp_rel(struct x86_emulate_ctxt *ctxt, int rel)
>  {
> -	register_address_increment(ctxt, &ctxt->_eip, rel);
> +	/* 64-bit mode relative jumps are always 64-bit; otherwise mask */
> +	int op_bytes = ctxt->mode == X86EMUL_MODE_PROT64 ? 8 : ctxt->op_bytes;

Just a nit, probably break this up for readability ?

> +	masked_increment(&ctxt->eip, op_bytes, rel);
>  }
>  
>  static u32 desc_limit_scaled(struct desc_struct *desc)
--
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