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

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Message-ID: <536A57E4.10704@gmail.com>
Date:	Wed, 07 May 2014 18:57:24 +0300
From:	Nadav Amit <nadav.amit@...il.com>
To:	Bandan Das <bsd@...hat.com>, 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

On 5/7/14, 5:43 PM, Bandan Das wrote:
> 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 ?
>
I will make it more readable on the next version.

Thanks,
Nadav
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