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

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Date:	Thu,  7 May 2015 14:47:50 +0200
From:	Nicholas Mc Guire <hofrat@...dl.org>
To:	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,
	Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH] MIPS: KVM: do not sign extend on unsigned MMIO load

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>
---

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:
-- 
1.7.10.4

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