Re: [PATCH] KVM: PPC: fix oops when checking KVM_CAP_PPC_HTM

From: Michael Ellerman <mpe@ellerman.id.au>
To: Greg Kurz <groug@kaod.org>, kvm@vger.kernel.org
Cc: kvm-ppc@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
	stable@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	linuxppc-dev@lists.ozlabs.org,
	Sam Bobroff <sam.bobroff@au1.ibm.com>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH] KVM: PPC: fix oops when checking KVM_CAP_PPC_HTM
Date: Thu, 12 Oct 2017 22:27:54 +1100	[thread overview]
Message-ID: <87wp40txl1.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <150542618501.6859.11512107352972110416.stgit@bahia.lan>

Greg Kurz <groug@kaod.org> writes:
> The following program causes a kernel oops:
>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/ioctl.h>
> #include <linux/kvm.h>
>
> main()
> {
>     int fd = open("/dev/kvm", O_RDWR);
>     ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_PPC_HTM);
> }
>
> This happens because when using the global KVM fd with
> KVM_CHECK_EXTENSION, kvm_vm_ioctl_check_extension() gets
> called with a NULL kvm argument, which gets dereferenced
> in is_kvmppc_hv_enabled(). Spotted while reading the code.
>
> Let's use the hv_enabled fallback variable, like everywhere
> else in this function.
>
> Fixes: 23528bb21ee2 ("KVM: PPC: Introduce KVM_CAP_PPC_HTM")
> Cc: stable@vger.kernel.org # v4.7+
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>  arch/powerpc/kvm/powerpc.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 3480faaf1ef8..ee279c7f4802 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -644,8 +644,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		break;
>  #endif
>  	case KVM_CAP_PPC_HTM:
> -		r = cpu_has_feature(CPU_FTR_TM_COMP) &&
> -		    is_kvmppc_hv_enabled(kvm);
> +		r = cpu_has_feature(CPU_FTR_TM_COMP) && hv_enabled;
>  		break;
>  	default:
>  		r = 0;

Did this go anywhere?

cheers