[PATCH 4.19 166/170] KVM: arm/arm64: vgic: Fix off-by-one bug in vgic_get_irq()

From: Greg Kroah-Hartman
Date: Mon Jan 07 2019 - 07:59:14 EST

4.19-stable review patch. If anyone has any objections, please let me know.


From: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

commit c23b2e6fc4ca346018618266bcabd335c0a8a49e upstream.

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

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@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
[dropped the SPI part which was fixed separately]
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

virt/kvm/arm/vgic/vgic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -103,7 +103,7 @@ struct vgic_irq *vgic_get_irq(struct kvm
/* 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];