linux-kernel - Re: [PATCH] MIPS: KVM: do not sign extend on unsigned MMIO load

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Message-ID: <554CC530.20906@imgtec.com>
Date:	Fri, 8 May 2015 15:16:16 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Nicholas Mc Guire <hofrat@...dl.org>,
	Gleb Natapov <gleb@...nel.org>
CC:	Paolo Bonzini <pbonzini@...hat.com>,
	Ralf Baechle <ralf@...ux-mips.org>, <kvm@...r.kernel.org>,
	<linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: KVM: do not sign extend on unsigned MMIO load

On 07/05/15 13:47, Nicholas Mc Guire wrote:
> Fix possible unintended sign extension in unsigned MMIO loads by casting
> to uint16_t in the case of mmio_needed != 2.
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>

Looks good to me. I wrote an MMIO test to reproduce the issue, and this
fixes it.

Reviewed-by: James Hogan <james.hogan@...tec.com>
Tested-by: James Hogan <james.hogan@...tec.com>

It looks suitable for stable too (3.10+).

Cheers
James

> ---
> 
> Thanks to James Hogan <james.hogan@...tec.com> for the explaination of 
> mmio_needed (there is not really any helpful comment in the code on this)
> in this case (mmio_needed!=2) it should be unsigned.
> 
> Patch was only compile tested msp71xx_defconfig + CONFIG_KVM=m
> 
> Patch is against 4.1-rc2 (localversion-next is -next-20150506)
> 
>  arch/mips/kvm/emulate.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
> index 6230f37..2f0fc60 100644
> --- a/arch/mips/kvm/emulate.c
> +++ b/arch/mips/kvm/emulate.c
> @@ -2415,7 +2415,7 @@ enum emulation_result kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu,
>  		if (vcpu->mmio_needed == 2)
>  			*gpr = *(int16_t *) run->mmio.data;
>  		else
> -			*gpr = *(int16_t *) run->mmio.data;
> +			*gpr = *(uint16_t *)run->mmio.data;
>  
>  		break;
>  	case 1:
> 


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