| Message ID | 20170222160119.52771-4-pasic@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the > reward for trying to migrate an array with some null pointers in it was > an illegal memory access, that is a swift and painless death of the > process. Let's make vmstate cope with this scenario. > > The general approach is, when we encounter a null pointer (element), > instead of following the pointer to save/load the data behind it, we > save/load a placeholder. This way we can detect if we expected a null > pointer at the load side but not null data was saved instead. > > Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com> > Reviewed-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > --- > We will need this to load/save some on demand created state in the > (s390x) channel subsystem (see ChannelSubSys.css in hw/s390x/css.c for > an example). > --- > include/migration/vmstate.h | 4 ++++ > migration/vmstate.c | 40 ++++++++++++++++++++++++++++++++++++++-- > 2 files changed, 42 insertions(+), 2 deletions(-) > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h > index 63e7b02..f2dbf84 100644 > --- a/include/migration/vmstate.h > +++ b/include/migration/vmstate.h > @@ -253,6 +253,10 @@ extern const VMStateInfo vmstate_info_uint16; > extern const VMStateInfo vmstate_info_uint32; > extern const VMStateInfo vmstate_info_uint64; > > +/** Put this in the stream when migrating a null pointer.*/ > +#define VMS_NULLPTR_MARKER (0x30U) /* '0' */ > +extern const VMStateInfo vmstate_info_nullptr; > + > extern const VMStateInfo vmstate_info_float64; > extern const VMStateInfo vmstate_info_cpudouble; > > diff --git a/migration/vmstate.c b/migration/vmstate.c > index 836a7a4..78b3cd4 100644 > --- a/migration/vmstate.c > +++ b/migration/vmstate.c > @@ -117,7 +117,11 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd, > if (field->flags & VMS_ARRAY_OF_POINTER) { > curr_elem = *(void **)curr_elem; > } > - if (field->flags & VMS_STRUCT) { > + if (!curr_elem) { > + /* if null pointer check placeholder and do not follow */ > + assert(field->flags & VMS_ARRAY_OF_POINTER); > + ret = vmstate_info_nullptr.get(f, curr_elem, size, NULL); > + } else if (field->flags & VMS_STRUCT) { > ret = vmstate_load_state(f, field->vmsd, curr_elem, > field->vmsd->version_id); > } else { > @@ -332,7 +336,11 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd, > assert(curr_elem); > curr_elem = *(void **)curr_elem; > } > - if (field->flags & VMS_STRUCT) { > + if (!curr_elem) { > + /* if null pointer write placeholder and do not follow */ > + assert(field->flags & VMS_ARRAY_OF_POINTER); > + vmstate_info_nullptr.put(f, curr_elem, size, NULL, NULL); > + } else if (field->flags & VMS_STRUCT) { > vmstate_save_state(f, field->vmsd, curr_elem, vmdesc_loop); > } else { > field->info->put(f, curr_elem, size, field, vmdesc_loop); > @@ -747,6 +755,34 @@ const VMStateInfo vmstate_info_uint64 = { > .put = put_uint64, > }; > > +static int get_nullptr(QEMUFile *f, void *pv, size_t size, VMStateField *field) > + > +{ > + if (qemu_get_byte(f) == VMS_NULLPTR_MARKER) { > + return 0; > + } > + error_report("vmstate: get_nullptr expected VMS_NULLPTR_MARKER"); > + return -EINVAL; > +} > + > +static int put_nullptr(QEMUFile *f, void *pv, size_t size, > + VMStateField *field, QJSON *vmdesc) > + > +{ > + if (pv == NULL) { > + qemu_put_byte(f, VMS_NULLPTR_MARKER); > + return 0; > + } > + error_report("vmstate: put_nullptr must be called with pv == NULL"); > + return -EINVAL; > +} > + > +const VMStateInfo vmstate_info_nullptr = { > + .name = "uint64", > + .get = get_nullptr, > + .put = put_nullptr, > +}; > + > /* 64 bit unsigned int. See that the received value is the same than the one > in the field */ > > -- > 2.8.4 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On 02/24/2017 01:29 PM, Dr. David Alan Gilbert wrote: > * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: >> Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the >> reward for trying to migrate an array with some null pointers in it was >> an illegal memory access, that is a swift and painless death of the >> process. Let's make vmstate cope with this scenario. >> >> The general approach is, when we encounter a null pointer (element), >> instead of following the pointer to save/load the data behind it, we >> save/load a placeholder. This way we can detect if we expected a null >> pointer at the load side but not null data was saved instead. >> >> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com> >> Reviewed-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com> > > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > Thanks! Seems there are no further objections. Is the series going in via your tree (softfreeze starting 28.02, me worried)? Regards, Halil
* Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > > > On 02/24/2017 01:29 PM, Dr. David Alan Gilbert wrote: > > * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > >> Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the > >> reward for trying to migrate an array with some null pointers in it was > >> an illegal memory access, that is a swift and painless death of the > >> process. Let's make vmstate cope with this scenario. > >> > >> The general approach is, when we encounter a null pointer (element), > >> instead of following the pointer to save/load the data behind it, we > >> save/load a placeholder. This way we can detect if we expected a null > >> pointer at the load side but not null data was saved instead. > >> > >> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com> > >> Reviewed-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com> > > > > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > > > > Thanks! Seems there are no further objections. Is the series going in > via your tree (softfreeze starting 28.02, me worried)? I'm ok with that; and there will be a migration pull tomorrow. So lets see what we can do. Dave > > Regards, > Halil > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h index 63e7b02..f2dbf84 100644 --- a/include/migration/vmstate.h +++ b/include/migration/vmstate.h @@ -253,6 +253,10 @@ extern const VMStateInfo vmstate_info_uint16; extern const VMStateInfo vmstate_info_uint32; extern const VMStateInfo vmstate_info_uint64; +/** Put this in the stream when migrating a null pointer.*/ +#define VMS_NULLPTR_MARKER (0x30U) /* '0' */ +extern const VMStateInfo vmstate_info_nullptr; + extern const VMStateInfo vmstate_info_float64; extern const VMStateInfo vmstate_info_cpudouble; diff --git a/migration/vmstate.c b/migration/vmstate.c index 836a7a4..78b3cd4 100644 --- a/migration/vmstate.c +++ b/migration/vmstate.c @@ -117,7 +117,11 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd, if (field->flags & VMS_ARRAY_OF_POINTER) { curr_elem = *(void **)curr_elem; } - if (field->flags & VMS_STRUCT) { + if (!curr_elem) { + /* if null pointer check placeholder and do not follow */ + assert(field->flags & VMS_ARRAY_OF_POINTER); + ret = vmstate_info_nullptr.get(f, curr_elem, size, NULL); + } else if (field->flags & VMS_STRUCT) { ret = vmstate_load_state(f, field->vmsd, curr_elem, field->vmsd->version_id); } else { @@ -332,7 +336,11 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd, assert(curr_elem); curr_elem = *(void **)curr_elem; } - if (field->flags & VMS_STRUCT) { + if (!curr_elem) { + /* if null pointer write placeholder and do not follow */ + assert(field->flags & VMS_ARRAY_OF_POINTER); + vmstate_info_nullptr.put(f, curr_elem, size, NULL, NULL); + } else if (field->flags & VMS_STRUCT) { vmstate_save_state(f, field->vmsd, curr_elem, vmdesc_loop); } else { field->info->put(f, curr_elem, size, field, vmdesc_loop); @@ -747,6 +755,34 @@ const VMStateInfo vmstate_info_uint64 = { .put = put_uint64, }; +static int get_nullptr(QEMUFile *f, void *pv, size_t size, VMStateField *field) + +{ + if (qemu_get_byte(f) == VMS_NULLPTR_MARKER) { + return 0; + } + error_report("vmstate: get_nullptr expected VMS_NULLPTR_MARKER"); + return -EINVAL; +} + +static int put_nullptr(QEMUFile *f, void *pv, size_t size, + VMStateField *field, QJSON *vmdesc) + +{ + if (pv == NULL) { + qemu_put_byte(f, VMS_NULLPTR_MARKER); + return 0; + } + error_report("vmstate: put_nullptr must be called with pv == NULL"); + return -EINVAL; +} + +const VMStateInfo vmstate_info_nullptr = { + .name = "uint64", + .get = get_nullptr, + .put = put_nullptr, +}; + /* 64 bit unsigned int. See that the received value is the same than the one in the field */