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

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Message-ID: <536A586B.2060200@redhat.com>
Date:	Wed, 07 May 2014 17:59:39 +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 5/5] KVM: x86: Fix wrong masking on relative jump/call

Il 07/05/2014 14:32, Nadav Amit ha scritto:
> 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.

The SDM says "If the operand-size attribute is 16, the upper two bytes 
of the EIP register are cleared, resulting in a maximum instruction 
pointer size of 16 bits".  I'm not sure whether that should also imply 
that 63:32 are _not_ unmodified (because you do a 32-bit write not a 
16-bit one), but in any case it looks like masked_increment is not the 
right function.

Paolo

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