KVM: SVM: Initialize prev_ga_tag before use

commit f6426ab9c957e97418ac5b0466538792767b1738 upstream.

The function amd_ir_set_vcpu_affinity makes use of the parameter struct
amd_iommu_pi_data.prev_ga_tag to determine if it should delete struct
amd_iommu_pi_data from a list when not running in AVIC mode.

However, prev_ga_tag is initialized only when AVIC is enabled. The non-zero
uninitialized value can cause unintended code path, which ends up making
use of the struct vcpu_svm.ir_list and ir_list_lock without being
initialized (since they are intended only for the AVIC case).

This triggers NULL pointer dereference bug in the function vm_ir_list_del
with the following call trace:

    svm_update_pi_irte+0x3c2/0x550 [kvm_amd]
    ? proc_create_single_data+0x41/0x50
    kvm_arch_irq_bypass_add_producer+0x40/0x60 [kvm]
    __connect+0x5f/0xb0 [irqbypass]
    irq_bypass_register_producer+0xf8/0x120 [irqbypass]
    vfio_msi_set_vector_signal+0x1de/0x2d0 [vfio_pci]
    vfio_msi_set_block+0x77/0xe0 [vfio_pci]
    vfio_pci_set_msi_trigger+0x25c/0x2f0 [vfio_pci]
    vfio_pci_set_irqs_ioctl+0x88/0xb0 [vfio_pci]
    vfio_pci_ioctl+0x2ea/0xed0 [vfio_pci]
    ? alloc_file_pseudo+0xa5/0x100
    vfio_device_fops_unl_ioctl+0x26/0x30 [vfio]
    ? vfio_device_fops_unl_ioctl+0x26/0x30 [vfio]
    __x64_sys_ioctl+0x96/0xd0
    do_syscall_64+0x37/0x80
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

Therefore, initialize prev_ga_tag to zero before use. This should be safe
because ga_tag value 0 is invalid (see function avic_vm_init).

Fixes: dfa20099e26e ("KVM: SVM: Refactor AVIC vcpu initialization into avic_init_vcpu()")
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Message-Id: <20201003232707.4662-1-suravee.suthikulpanit@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 78826d123fb86b83fcab8540c00b8f5fbb25924e..cfd6e58e824b3c578482780185835817ef97e1f2 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4862,6 +4862,7 @@ static int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
                         * - Tell IOMMU to use legacy mode for this interrupt.
                         * - Retrieve ga_tag of prior interrupt remapping data.
                         */
+                       pi.prev_ga_tag = 0;
                        pi.is_guest_mode = false;
                        ret = irq_set_vcpu_affinity(host_irq, &pi);