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

From: Greg Kurz <[email-masked]>
Date: Thu, 12 Oct 2017 14:51:57 +0200

On Thu, 12 Oct 2017 22:27:54 +1100
Michael Ellerman <[email-masked]> wrote:

> Greg Kurz <[email-masked]> 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: [email-masked] # v4.7+
> > Signed-off-by: Greg Kurz <[email-masked]>
> > ---
> >  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

I'm afraid not... and I haven't tried to ping Paul yet, since he's
supposed to be on vacation from what I've been told.