Re: [PATCH 2/2] spapr/nvram: Allocate enough space for all -prom-env options

[Greg Kurz <groug@kaod.org>]

On Tue, 11 Aug 2020 18:05:21 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> On 11/08/2020 17:30, Greg Kurz wrote:
> > Since commit 61f20b9dc5b7 ("spapr_nvram: Pre-initialize the NVRAM to
> > support the -prom-env parameter"), pseries machines can pre-initialize
> > the "system" partition in the NVRAM with the data passed to all -prom-env
> > parameters on the QEMU command line.
> > 
> > In this cases it is assumed that all the data fits in 64 KiB, but the user
> > can easily pass more and crash QEMU:
> > 
> > $ qemu-system-ppc64 -M pseries $(for ((x=0;x<128;x++)); do \
> >   echo -n " -prom-env "$(for ((y=0;y<1024;y++)); do echo -n x ; done) ; \
> >   done) # this requires ~128 Kib
> > malloc(): corrupted top size
> > Aborted (core dumped)
> > 
> > Call chrp_nvram_create_system_partition() first with its recently added
> > parameter dry_run set to false, to know the required size and allocate
> > the NVRAM buffer accordingly.
> > 
> > Fixes: 61f20b9dc5b7 ("spapr_nvram: Pre-initialize the NVRAM to support the -prom-env parameter")
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> >  hw/nvram/spapr_nvram.c |    4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/hw/nvram/spapr_nvram.c b/hw/nvram/spapr_nvram.c
> > index 992b818d34e7..1b74bec6200a 100644
> > --- a/hw/nvram/spapr_nvram.c
> > +++ b/hw/nvram/spapr_nvram.c
> > @@ -165,6 +165,10 @@ static void spapr_nvram_realize(SpaprVioDevice *dev, Error **errp)
> >          if (ret < 0) {
> >              return;
> >          }
> > +    } else if (nb_prom_envs > 0) {
> > +        nvram->size = chrp_nvram_create_system_partition(NULL,
> > +                                                         MIN_NVRAM_SIZE / 4,
> > +                                                         true);
> 
> I think this will break the migration: the prom-env parameters can be on
> the source side without being on the dest side. And so the pram size

Huh ? Migration mandates to have the same arguments on the command line,
and libvirt buys us that AFAIK or am I missing something ?

> will differ and the migration will fail.
> 
> Thanks,
> Laurent
>