2021-05-05 22:25:19

by Thomas Gleixner

Subject: KVM: x86: Cancel pvclock_gtod_work on module removal

Nothing prevents the following:

pvclock_gtod_notify()
queue_work(system_long_wq, &pvclock_gtod_work);
...
remove_module(kvm);
...
work_queue_run()
pvclock_gtod_work() <- UAF

Ditto for any other operation on that workqueue list head which touches
pvclock_gtod_work after module removal.

Cancel the work in kvm_arch_exit() to prevent that.

Fixes: 16e8d74d2da9 ("KVM: x86: notifier for clocksource changes")
Signed-off-by: Thomas Gleixner <[email protected]>
---
Found by inspection because of:
https://lkml.kernel.org/r/[email protected]
See also:
https://lkml.kernel.org/r/[email protected]

TL;DR: Scheduling work with tk_core.seq write held is a bad idea.
---
arch/x86/kvm/x86.c | 1 +
1 file changed, 1 insertion(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8168,6 +8168,7 @@ void kvm_arch_exit(void)
cpuhp_remove_state_nocalls(CPUHP_AP_X86_KVM_CLK_ONLINE);
#ifdef CONFIG_X86_64
pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
+ cancel_work_sync(&pvclock_gtod_work);
#endif
kvm_x86_ops.hardware_enable = NULL;
kvm_mmu_module_exit();

2021-05-06 11:38:53

by Paolo Bonzini

Subject: Re: KVM: x86: Cancel pvclock_gtod_work on module removal

On 05/05/21 23:48, Thomas Gleixner wrote:
> Nothing prevents the following:
>
> pvclock_gtod_notify()
> queue_work(system_long_wq, &pvclock_gtod_work);
> ...
> remove_module(kvm);
> ...
> work_queue_run()
> pvclock_gtod_work() <- UAF
>
> Ditto for any other operation on that workqueue list head which touches
> pvclock_gtod_work after module removal.
>
> Cancel the work in kvm_arch_exit() to prevent that.
>
> Fixes: 16e8d74d2da9 ("KVM: x86: notifier for clocksource changes")
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---
> Found by inspection because of:
> https://lkml.kernel.org/r/[email protected]
> See also:
> https://lkml.kernel.org/r/[email protected]
>
> TL;DR: Scheduling work with tk_core.seq write held is a bad idea.
> ---
> arch/x86/kvm/x86.c | 1 +
> 1 file changed, 1 insertion(+)
>
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8168,6 +8168,7 @@ void kvm_arch_exit(void)
> cpuhp_remove_state_nocalls(CPUHP_AP_X86_KVM_CLK_ONLINE);
> #ifdef CONFIG_X86_64
> pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
> + cancel_work_sync(&pvclock_gtod_work);
> #endif
> kvm_x86_ops.hardware_enable = NULL;
> kvm_mmu_module_exit();
>

Queued, thanks (with added Cc to stable).

Paolo