On Mon, Feb 18, 2019 at 11:52:18AM +0000, Daniel P. Berrangé 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 <ppan...@redhat.com> wrote: > > > > > From: Prasad J Pandit <p...@fedoraproject.org> > > > > > > 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 <berra...@redhat.com> > > > Fix-suggested-by: Daniel P. Berrangé <berra...@redhat.com> > > > Signed-off-by: Prasad J Pandit <p...@fedoraproject.org> > > > --- > > > 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.
So, Markus was saying at the last KVM Forum - and I agree with him -
that using "must maintain compatibility" as if its holy writ isn't
actually very sensible. It's always a tradeoff, and we need to engage
with that tradeoff on a case by case basis.
In this case the security hole it fixes is pretty small - but the
chances of realistically breaking the guests is also very small.
--
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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