Ack: Re: [maverick CVE 1/1] KVM: x86: Prevent starting PIT timers in the absence of irqchip support

[Brad Figg]

On 01/03/2012 09:31 AM, Andy Whitcroft wrote:
> From: Jan Kiszka<jan.kiszka at siemens.com>
>
> User space may create the PIT and forgets about setting up the irqchips.
> In that case, firing PIT IRQs will crash the host:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000128
> IP: [<ffffffffa10f6280>] kvm_set_irq+0x30/0x170 [kvm]
> ...
> Call Trace:
>   [<ffffffffa11228c1>] pit_do_work+0x51/0xd0 [kvm]
>   [<ffffffff81071431>] process_one_work+0x111/0x4d0
>   [<ffffffff81071bb2>] worker_thread+0x152/0x340
>   [<ffffffff81075c8e>] kthread+0x7e/0x90
>   [<ffffffff815a4474>] kernel_thread_helper+0x4/0x10
>
> Prevent this by checking the irqchip mode before starting a timer. We
> can't deny creating the PIT if the irqchips aren't set up yet as
> current user land expects this order to work.
>
> Signed-off-by: Jan Kiszka<jan.kiszka at siemens.com>
> Signed-off-by: Marcelo Tosatti<mtosatti at redhat.com>
>
> (cherry picked from commit 0924ab2cfa98b1ece26c033d696651fd62896c69)
> CVE-2011-4622
> BugLink: http://bugs.launchpad.net/bugs/911303
> Signed-off-by: Andy Whitcroft<apw at canonical.com>
> ---
>   arch/x86/kvm/i8254.c |   10 +++++++---
>   1 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> index 0150aff..ac06e2a 100644
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -280,11 +280,15 @@ static struct kvm_timer_ops kpit_ops = {
>   	.is_periodic = kpit_is_periodic,
>   };
>
> -static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
> +static void create_pit_timer(struct kvm *kvm, u32 val, int is_period)
>   {
> +	struct kvm_kpit_state *ps =&kvm->arch.vpit->pit_state;
>   	struct kvm_timer *pt =&ps->pit_timer;
>   	s64 interval;
>
> +	if (!irqchip_in_kernel(kvm))
> +		return;
> +
>   	interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ);
>
>   	pr_debug("create pit timer, interval is %llu nsec\n", interval);
> @@ -336,13 +340,13 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
>           /* FIXME: enhance mode 4 precision */
>   	case 4:
>   		if (!(ps->flags&  KVM_PIT_FLAGS_HPET_LEGACY)) {
> -			create_pit_timer(ps, val, 0);
> +			create_pit_timer(kvm, val, 0);
>   		}
>   		break;
>   	case 2:
>   	case 3:
>   		if (!(ps->flags&  KVM_PIT_FLAGS_HPET_LEGACY)){
> -			create_pit_timer(ps, val, 1);
> +			create_pit_timer(kvm, val, 1);
>   		}
>   		break;
>   	default:


-- 
Brad Figg brad.figg at canonical.com http://www.canonical.com