linux-kernel - [PATCH AUTOSEL 4.18 54/88] KVM: arm/arm64: vgic: Fix possible spectre-v1 write in vgic_mmio_write

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Date:   Fri, 7 Sep 2018 00:36:31 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Mark Rutland <mark.rutland@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 54/88] KVM: arm/arm64: vgic: Fix possible
 spectre-v1 write in vgic_mmio_write_apr()

From: Mark Rutland <mark.rutland@....com>

[ Upstream commit 6b8b9a48545e08345b8ff77c9fd51b1aebdbefb3 ]

It's possible for userspace to control n. Sanitize n when using it as an
array index, to inhibit the potential spectre-v1 write gadget.

Note that while it appears that n must be bound to the interval [0,3]
due to the way it is extracted from addr, we cannot guarantee that
compiler transformations (and/or future refactoring) will ensure this is
the case, and given this is a slow path it's better to always perform
the masking.

Found by smatch.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Christoffer Dall <christoffer.dall@....com>
Cc: Marc Zyngier <marc.zyngier@....com>
Cc: kvmarm@...ts.cs.columbia.edu
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 virt/kvm/arm/vgic/vgic-mmio-v2.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-mmio-v2.c
index ffc587bf4742..64e571cc02df 100644
--- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
+++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
@@ -352,6 +352,9 @@ static void vgic_mmio_write_apr(struct kvm_vcpu *vcpu,
 
 		if (n > vgic_v3_max_apr_idx(vcpu))
 			return;
+
+		n = array_index_nospec(n, 4);
+
 		/* GICv3 only uses ICH_AP1Rn for memory mapped (GICv2) guests */
 		vgicv3->vgic_ap1r[n] = val;
 	}
-- 
2.17.1