On Thu, Sep 14, 2017 at 11:56:25PM +0200, Greg Kurz wrote:
> 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@xxxxxxxxxxxxxxx # v4.7+
> Signed-off-by: Greg Kurz <groug@xxxxxxxx>
I don't think this is right. I'm pretty sure you want to fall back to
hv_enabled *only when* kvm is NULL. Otherwise if you have a PR guest
on an HV capable machine, this will give the wrong answer, when called
for that specific VM.
> ---
> 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;
>
--
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
Attachment:
signature.asc
Description: PGP signature