Re: [PATCH] KVM: Fix wallclock version writing race

[Avi Kivity <avi@redhat.com>]

On 05/04/2010 03:02 PM, Avi Kivity wrote:
> Wallclock writing uses an unprotected global variable to hold the version;
> this can cause one guest to interfere with another if both write their
> wallclock at the same time.
>
> Signed-off-by: Avi Kivity<avi@redhat.com>
>    

This was pointed out by Naphtali.

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f6f8dad..c3152d7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -754,14 +754,22 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
>
>   static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
>   {
> -	static int version;
> +	int version;
> +	int r;
>   	struct pvclock_wall_clock wc;
>   	struct timespec boot;
>
>   	if (!wall_clock)
>   		return;
>
> -	version++;
> +	r = kvm_read_guest(kvm, wall_clock,&version, sizeof(version));
> +	if (r)
> +		return;
> +
> +	if (version&  1)
> +		++version;  /* first time write, random junk */
> +
> +	++version;
>
>   	kvm_write_guest(kvm, wall_clock,&version, sizeof(version));
>
>    


-- 
error compiling committee.c: too many arguments to function