Re: [Qemu-ppc] [PATCH v3] ppc: add host-serial and host-model machine attributes

[Greg Kurz]

On Mon, 18 Feb 2019 11:52:18 +0000
Daniel P. Berrangé <address@hidden> wrote:

> On Mon, Feb 18, 2019 at 12:38:11PM +0100, Greg Kurz wrote:
> > On Mon, 18 Feb 2019 15:42:18 +0530
> > P J P <address@hidden> wrote:
> >   
> > > From: Prasad J Pandit <address@hidden>
> > > 
> > > On ppc hosts, hypervisor shares following system attributes
> > > 
> > >   - /proc/device-tree/system-id
> > >   - /proc/device-tree/model
> > > 
> > > with a guest. This could lead to information leakage and misuse.[*]
> > > Add machine attributes to control such system information exposure
> > > to a guest.
> > > 
> > > [*] https://wiki.openstack.org/wiki/OSSN/OSSN-0028
> > > 
> > > Reported-by: Daniel P. Berrangé <address@hidden>
> > > Fix-suggested-by: Daniel P. Berrangé <address@hidden>
> > > Signed-off-by: Prasad J Pandit <address@hidden>
> > > ---
> > >  hw/ppc/spapr.c         | 79 ++++++++++++++++++++++++++++++++++++++----
> > >  include/hw/ppc/spapr.h |  2 ++
> > >  2 files changed, 75 insertions(+), 6 deletions(-)
> > > 
> > > Update v3: move host-serial,host-model options to ppc sPAPR machine  
> > >   -> https://lists.gnu.org/archive/html/qemu-devel/2019-02/msg03182.html  
> > >   
> > > 
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index 0942f35bf8..666e500376 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -1249,13 +1249,30 @@ static void *spapr_build_fdt(sPAPRMachineState 
> > > *spapr,
> > >       * Add info to guest to indentify which host is it being run on
> > >       * and what is the uuid of the guest
> > >       */
> > > -    if (kvmppc_get_host_model(&buf)) {
> > > -        _FDT(fdt_setprop_string(fdt, 0, "host-model", buf));
> > > -        g_free(buf);
> > > +    if (spapr->host_model && !g_str_equal(spapr->host_model, "none")) {
> > > +        if (g_str_equal(spapr->host_model, "passthrough")) {
> > > +            /* -M host-model=passthrough */
> > > +            if (kvmppc_get_host_model(&buf)) {
> > > +                _FDT(fdt_setprop_string(fdt, 0, "host-model", buf));
> > > +                g_free(buf);
> > > +            }
> > > +        } else {
> > > +            /* -M host-model=<user-string> */
> > > +            _FDT(fdt_setprop_string(fdt, 0, "host-model", 
> > > spapr->host_model));
> > > +        }
> > >      }
> > > -    if (kvmppc_get_host_serial(&buf)) {
> > > -        _FDT(fdt_setprop_string(fdt, 0, "host-serial", buf));
> > > -        g_free(buf);
> > > +
> > > +    if (spapr->host_serial && !g_str_equal(spapr->host_serial, "none")) {
> > > +        if (g_str_equal(spapr->host_serial, "passthrough")) {
> > > +            /* -M host-serial=passthrough */
> > > +            if (kvmppc_get_host_serial(&buf)) {
> > > +                _FDT(fdt_setprop_string(fdt, 0, "host-serial", buf));
> > > +                g_free(buf);
> > > +            }
> > > +        } else {
> > > +            /* -M host-serial=<user-string> */
> > > +            _FDT(fdt_setprop_string(fdt, 0, "host-serial", 
> > > spapr->host_serial));
> > > +        }
> > >      }
> > >  
> > >      buf = qemu_uuid_unparse_strdup(&qemu_uuid);
> > > @@ -3138,6 +3155,36 @@ static void spapr_set_ic_mode(Object *obj, const 
> > > char *value, Error **errp)
> > >      }
> > >  }
> > >  
> > > +static char *spapr_get_host_model(Object *obj, Error **errp)
> > > +{
> > > +    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > > +
> > > +    return g_strdup(spapr->host_model);
> > > +}
> > > +
> > > +static void spapr_set_host_model(Object *obj, const char *value, Error 
> > > **errp)
> > > +{
> > > +    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > > +
> > > +    g_free(spapr->host_model);
> > > +    spapr->host_model = g_strdup(value);
> > > +}
> > > +
> > > +static char *spapr_get_host_serial(Object *obj, Error **errp)
> > > +{
> > > +    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > > +
> > > +    return g_strdup(spapr->host_serial);
> > > +}
> > > +
> > > +static void spapr_set_host_serial(Object *obj, const char *value, Error 
> > > **errp)
> > > +{
> > > +    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > > +
> > > +    g_free(spapr->host_serial);
> > > +    spapr->host_serial = g_strdup(value);
> > > +}
> > > +
> > >  static void spapr_instance_init(Object *obj)
> > >  {
> > >      sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > > @@ -3183,6 +3230,20 @@ static void spapr_instance_init(Object *obj)
> > >      object_property_set_description(obj, "ic-mode",
> > >                   "Specifies the interrupt controller mode (xics, xive, 
> > > dual)",
> > >                   NULL);
> > > +
> > > +    spapr->host_model = NULL;  
> > 
> > This isn't needed since object_initialize_with_type() already takes care
> > of zeroing the instance for us.
> >   
> > > +    object_property_add_str(obj, "host-model",
> > > +        spapr_get_host_model, spapr_set_host_model,
> > > +        &error_abort);
> > > +    object_property_set_description(obj, "host-model",
> > > +        "Set host's model-id to use - none|passthrough|string", 
> > > &error_abort);
> > > +
> > > +    spapr->host_serial = NULL;  
> > 
> > Same here.
> >   
> > > +    object_property_add_str(obj, "host-serial",
> > > +        spapr_get_host_serial, spapr_set_host_serial,
> > > +        &error_abort);
> > > +    object_property_set_description(obj, "host-serial",
> > > +        "Set host's system-id to use - none|passthrough|string", 
> > > &error_abort);
> > >  }
> > >  
> > >  static void spapr_machine_finalizefn(Object *obj)
> > > @@ -4080,9 +4141,15 @@ DEFINE_SPAPR_MACHINE(4_0, "4.0", true);
> > >  static void spapr_machine_3_1_class_options(MachineClass *mc)
> > >  {
> > >      sPAPRMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
> > > +    static GlobalProperty compat[] = {
> > > +        { TYPE_SPAPR_MACHINE, "host-model", "passthrough" },
> > > +        { TYPE_SPAPR_MACHINE, "host-serial", "passthrough" },
> > > +    };
> > >    
> > 
> > So... we don't fix the information leak for older machines by default ? From
> > previous discussions, I understand it is for the sake of compatibility, but
> > leaving the burden of securing the host to downstream or to the user still
> > looks unsecure to me FWIW.  
> 
> Maintaining guest ABI compatibility has to take priority, even over
> fixing security issues, because we must never intentionally break
> guest OS/applications by silently altering guest ABI. This is one of
> the two reasons why machine type versioning exists (the other reason
> being live migration data stream).
> 
> This is nothing new - we've done it before for security flaws where
> a fix would involve changing guest ABI. This particular security flaw
> is pretty minor compared to other cases that we've left unfixed by
> default eg Meltdown / Spectre and is easily addressed by the user if
> needed.
> 
> Regards,
> Daniel

Alright then if there's prior consensus on compatibility versus security.

So, with or without the unneeded zeroing of the spapr->host_* fields:

Reviewed-by: Greg Kurz <address@hidden>