From 7d8b44c54e0c7c8f688e3a07f17e6083f849f01f Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Fri, 23 Mar 2018 14:57:09 +0000 Subject: [PATCH] KVM: arm/arm64: vgic-its: Fix potential overrun in vgic_copy_lpi_list vgic_copy_lpi_list() parses the LPI list and picks LPIs targeting a given vcpu. We allocate the array containing the intids before taking the lpi_list_lock, which means we can have an array size that is not equal to the number of LPIs. This is particularly obvious when looking at the path coming from vgic_enable_lpis, which is not a command, and thus can run in parallel with commands: vcpu 0: vcpu 1: vgic_enable_lpis its_sync_lpi_pending_table vgic_copy_lpi_list intids = kmalloc_array(irq_count) MAPI(lpi targeting vcpu 0) list_for_each_entry(lpi_list_head) intids[i++] = irq->intid; At that stage, we will happily overrun the intids array. Boo. An easy fix is is to break once the array is full. The MAPI command will update the config anyway, and we won't miss a thing. We also make sure that lpi_list_count is read exactly once, so that further updates of that value will not affect the array bound check. Cc: stable@vger.kernel.org Fixes: ccb1d791ab9e ("KVM: arm64: vgic-its: Fix pending table sync") Reviewed-by: Andre Przywara Reviewed-by: Eric Auger Signed-off-by: Marc Zyngier --- virt/kvm/arm/vgic/vgic-its.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c index 465095355666..a8f07243aa9f 100644 --- a/virt/kvm/arm/vgic/vgic-its.c +++ b/virt/kvm/arm/vgic/vgic-its.c @@ -316,21 +316,24 @@ static int vgic_copy_lpi_list(struct kvm_vcpu *vcpu, u32 **intid_ptr) struct vgic_dist *dist = &vcpu->kvm->arch.vgic; struct vgic_irq *irq; u32 *intids; - int irq_count = dist->lpi_list_count, i = 0; + int irq_count, i = 0; /* - * We use the current value of the list length, which may change - * after the kmalloc. We don't care, because the guest shouldn't - * change anything while the command handling is still running, - * and in the worst case we would miss a new IRQ, which one wouldn't - * expect to be covered by this command anyway. + * There is an obvious race between allocating the array and LPIs + * being mapped/unmapped. If we ended up here as a result of a + * command, we're safe (locks are held, preventing another + * command). If coming from another path (such as enabling LPIs), + * we must be careful not to overrun the array. */ + irq_count = READ_ONCE(dist->lpi_list_count); intids = kmalloc_array(irq_count, sizeof(intids[0]), GFP_KERNEL); if (!intids) return -ENOMEM; spin_lock(&dist->lpi_list_lock); list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) { + if (i == irq_count) + break; /* We don't need to "get" the IRQ, as we hold the list lock. */ if (irq->target_vcpu != vcpu) continue; -- 2.30.2