Hi Gustavo,
On 12/12/2018 20:11, Gustavo A. R. Silva wrote:
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> ---
> virt/kvm/arm/vgic/vgic.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 50e25438fb3c..5db40696055a 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -103,13 +103,13 @@ 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];
> }
>
> /* SPIs */
> if (intid <= VGIC_MAX_SPI) {
> - intid = array_index_nospec(intid, VGIC_MAX_SPI);
> + intid = array_index_nospec(intid, VGIC_MAX_SPI + 1);
> return &kvm->arch.vgic.spis[intid - VGIC_NR_PRIVATE_IRQS];
> }
>
>
That's a good one. Out of curiosity, how did you find it?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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