Subject: [PATCH] KVM: arm/arm64: check IRQ number on userland injection

From: [email-masked] (Christopher Covington)
Date: Fri, 10 Apr 2015 11:29:22 -0400

Hi Andre,

On 04/10/2015 11:17 AM, Andre Przywara wrote:
> When userland injects a SPI via the KVM_IRQ_LINE ioctl we currently
> only check it against a fixed limit, which historically is set
> to 127. With the new dynamic IRQ allocation the effective limit may
> actually be smaller (64).
> So when now a malicious or buggy userland injects a SPI in that
> range, we spill over on our VGIC bitmaps and bytemaps memory.
> I could trigger a host kernel NULL pointer dereference with current
> mainline by injecting some bogus IRQ number from a hacked kvmtool:

> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -195,7 +195,11 @@ struct kvm_arch_memory_slot {
>  #define KVM_ARM_IRQ_CPU_IRQ		0
>  #define KVM_ARM_IRQ_CPU_FIQ		1
>  
> -/* Highest supported SPI, from VGIC_NR_IRQS */
> +/*
> + * This used to hold the highest supported SPI, but it is now obsolete
> + * and only here to provide source code level compatibility with older
> + * userland. The highest SPI number can be set via KVM_DEV_ARM_VGIC_GRP_NR_IRQS.
> + */
>  #define KVM_ARM_IRQ_GIC_MAX		127

If that's the case should it maybe only defined when __KERNEL__ is not defined?

Chris

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