KVM: arm/arm64: vgic: fix possible spectre-v1 in vgic_mmio_read_apr()

It's possible for userspace to control n. Sanitize n when using it as an
array index.

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>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-mmio-v2.c
index e21e2f4..ffc587b 100644 (file)
--- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
+++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
@@ -14,6 +14,8 @@
 #include <linux/irqchip/arm-gic.h>
 #include <linux/kvm.h>
 #include <linux/kvm_host.h>
+#include <linux/nospec.h>
+
 #include <kvm/iodev.h>
 #include <kvm/arm_vgic.h>
 
@@ -324,6 +326,9 @@ static unsigned long vgic_mmio_read_apr(struct kvm_vcpu *vcpu,
 
                if (n > vgic_v3_max_apr_idx(vcpu))
                        return 0;
+
+               n = array_index_nospec(n, 4);
+
                /* GICv3 only uses ICH_AP1Rn for memory mapped (GICv2) guests */
                return vgicv3->vgic_ap1r[n];
        }