On 22/11/2016 20:20, Radim Krčmář wrote:
> Cluster xAPIC delivery incorrectly assumed that dest_id <= 0xff.
> With enabled KVM_X2APIC_API_USE_32BIT_IDS in KVM_CAP_X2APIC_API, a
> userspace can send an interrupt with dest_id that results in
> out-of-bounds access.
>
> Found by syzkaller:
>
> BUG: KASAN: slab-out-of-bounds in kvm_irq_delivery_to_apic_fast+0x11fa/0x1210 at addr ffff88003d9ca750
> Read of size 8 by task syz-executor/22923
> CPU: 0 PID: 22923 Comm: syz-executor Not tainted 4.9.0-rc4+ #49
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> [...]
> Call Trace:
> [...] __dump_stack lib/dump_stack.c:15
> [...] dump_stack+0xb3/0x118 lib/dump_stack.c:51
> [...] kasan_object_err+0x1c/0x70 mm/kasan/report.c:156
> [...] print_address_description mm/kasan/report.c:194
> [...] kasan_report_error mm/kasan/report.c:283
> [...] kasan_report+0x231/0x500 mm/kasan/report.c:303
> [...] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:329
> [...] kvm_irq_delivery_to_apic_fast+0x11fa/0x1210 arch/x86/kvm/lapic.c:824
> [...] kvm_irq_delivery_to_apic+0x132/0x9a0 arch/x86/kvm/irq_comm.c:72
> [...] kvm_set_msi+0x111/0x160 arch/x86/kvm/irq_comm.c:157
> [...] kvm_send_userspace_msi+0x201/0x280 arch/x86/kvm/../../../virt/kvm/irqchip.c:74
> [...] kvm_vm_ioctl+0xba5/0x1670 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3015
> [...] vfs_ioctl fs/ioctl.c:43
> [...] do_vfs_ioctl+0x18c/0x1040 fs/ioctl.c:679
> [...] SYSC_ioctl fs/ioctl.c:694
> [...] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
> [...] entry_SYSCALL_64_fastpath+0x1f/0xc2
>
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: e45115b62f9a ("KVM: x86: use physical LAPIC array for logical x2APIC")
> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> ---
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Steve Rutherford <srutherford@xxxxxxxxxx>
> ---
> arch/x86/kvm/lapic.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 09edd32b8e42..34a66b2d47e6 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -138,7 +138,7 @@ static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
> *mask = dest_id & 0xff;
> return true;
> case KVM_APIC_MODE_XAPIC_CLUSTER:
> - *cluster = map->xapic_cluster_map[dest_id >> 4];
> + *cluster = map->xapic_cluster_map[(dest_id >> 4) & 0xf];
> *mask = dest_id & 0xf;
> return true;
> default:
>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
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