Patch "KVM: arm/arm64: check IRQ number on userland injection" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

KVM: arm/arm64: check IRQ number on userland injection

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-arm-arm64-check-irq-number-on-userland-injection.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andre Przywara <[email protected]>
Date: Fri, 10 Apr 2015 16:17:59 +0100
Subject: KVM: arm/arm64: check IRQ number on userland injection

From: Andre Przywara <[email protected]>

commit fd1d0ddf2ae92fb3df42ed476939861806c5d785 upstream.

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:
-----------------
....
DEBUG: kvm_vgic_inject_irq(kvm, cpu=0, irq=114, level=1)
DEBUG: vgic_update_irq_pending(kvm, cpu=0, irq=114, level=1)
DEBUG: IRQ #114 still in the game, writing to bytemap now...

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = ffffffc07652e000
[00000000] *pgd=00000000f658b003, *pud=00000000f658b003, *pmd=0000000000000000
Internal error: Oops: 96000006 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 1053 Comm: lkvm-msi-irqinj Not tainted 4.0.0-rc7+ #3027
Hardware name: FVP Base (DT)
task: ffffffc0774e9680 ti: ffffffc0765a8000 task.ti: ffffffc0765a8000
PC is at kvm_vgic_inject_irq+0x234/0x310
LR is at kvm_vgic_inject_irq+0x30c/0x310
pc : [<ffffffc0000ae0a8>] lr : [<ffffffc0000ae180>] pstate: 80000145

.....

So this patch fixes this by checking the SPI number against the actual limit. Also we remove the former legacy hard limit of 127 in the ioctl code.

[maz: wrap KVM_ARM_IRQ_GIC_MAX with #ifndef __KERNEL__, as suggested by Christopher Covington]

---
 arch/arm/include/uapi/asm/kvm.h   |    8 +++++++-
 arch/arm/kvm/arm.c                |    3 +--
 arch/arm64/include/uapi/asm/kvm.h |    8 +++++++-
 virt/kvm/arm/vgic.c               |    3 +++
 4 files changed, 18 insertions(+), 4 deletions(-)

@@ -195,8 +195,14 @@ 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.
+ */
+#ifndef __KERNEL__
 #define KVM_ARM_IRQ_GIC_MAX		127
+#endif
 
 /* PSCI interface */
 #define KVM_PSCI_FN_BASE		0x95c1ba5e

@@ -651,8 +651,7 @@ int kvm_vm_ioctl_irq_line(struct kvm *kv
 		if (!irqchip_in_kernel(kvm))
 			return -ENXIO;
 
-		if (irq_num < VGIC_NR_PRIVATE_IRQS ||
-		    irq_num > KVM_ARM_IRQ_GIC_MAX)
+		if (irq_num < VGIC_NR_PRIVATE_IRQS)
 			return -EINVAL;
 
 		return kvm_vgic_inject_irq(kvm, 0, irq_num, level);

@@ -188,8 +188,14 @@ 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.
+ */
+#ifndef __KERNEL__
 #define KVM_ARM_IRQ_GIC_MAX		127
+#endif
 
 /* PSCI interface */
 #define KVM_PSCI_FN_BASE		0x95c1ba5e

@@ -1371,6 +1371,9 @@ int kvm_vgic_inject_irq(struct kvm *kvm,
 			goto out;
 	}
 
+	if (irq_num >= kvm->arch.vgic.nr_irqs)
+		return -EINVAL;
+
 	vcpu_id = vgic_update_irq_pending(kvm, cpuid, irq_num, level);
 	if (vcpu_id >= 0) {
 		/* kick the specified vcpu */

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/kvm-arm-arm64-check-irq-number-on-userland-injection.patch