KVM: arm/arm64: vgic: Fix off-by-one bug in vgic_get_irq()

When using the nospec API, it should be taken into account that:

"...if the CPU speculates past the bounds check then
 * array_index_nospec() will clamp the index within the range of [0,
 * size)."

The above is part of the header for macro array_index_nospec() in
linux/nospec.h

Now, in this particular case, if intid evaluates to exactly VGIC_MAX_SPI
or to exaclty VGIC_MAX_PRIVATE, the array_index_nospec() macro ends up
returning VGIC_MAX_SPI - 1 or VGIC_MAX_PRIVATE - 1 respectively, instead
of VGIC_MAX_SPI or VGIC_MAX_PRIVATE, which, based on the original logic:

	/* SGIs and PPIs */
	if (intid <= VGIC_MAX_PRIVATE)
 		return &vcpu->arch.vgic_cpu.private_irqs[intid];

 	/* SPIs */
	if (intid <= VGIC_MAX_SPI)
 		return &kvm->arch.vgic.spis[intid - VGIC_NR_PRIVATE_IRQS];

are valid values for intid.

Fix this by calling array_index_nospec() macro with VGIC_MAX_PRIVATE + 1
and VGIC_MAX_SPI + 1 as arguments for its parameter size.

Fixes: 41b87599c743 ("KVM: arm/arm64: vgic: fix possible spectre-v1 in vgic_get_irq()")
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
[dropped the SPI part which was fixed separately]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
CVE-2017-5753

(cherry picked from commit c23b2e6fc4ca346018618266bcabd335c0a8a49e)
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
index 4332bef09228e49c2318e9d365bf4f26dc0c66bc..d9679ce97298a2dfca64e587b9c7d90cea39fef2 100644 (file)
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -107,7 +107,7 @@ struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
 {
        /* SGIs and PPIs */
        if (intid <= VGIC_MAX_PRIVATE) {
-               intid = array_index_nospec(intid, VGIC_MAX_PRIVATE);
+               intid = array_index_nospec(intid, VGIC_MAX_PRIVATE + 1);
                return &vcpu->arch.vgic_cpu.private_irqs[intid];
        }