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    Subject[PATCH AUTOSEL 4.18 54/88] KVM: arm/arm64: vgic: Fix possible spectre-v1 write in vgic_mmio_write_apr()
    Date
    From: Mark Rutland <mark.rutland@arm.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@arm.com>
    Cc: Christoffer Dall <christoffer.dall@arm.com>
    Cc: Marc Zyngier <marc.zyngier@arm.com>
    Cc: kvmarm@lists.cs.columbia.edu
    Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.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
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