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

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Oct 12, 2017 at 02:51:57PM +0200, Greg Kurz wrote:
> On Thu, 12 Oct 2017 22:27:54 +1100
> Michael Ellerman <mpe@ellerman.id.au> wrote:
> 
> > 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
> 
> 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.

He's back now.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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