Re: [PATCH] KVM: x86: fix out-of-bounds access in lapic

[Paolo Bonzini]

On 22/11/2016 20:20, Radim KrÄmÃÅ 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 KrÄmÃÅ <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>