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

[Laurent Vivier <lvivier@redhat.com>]

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
will differ and the migration will fail.

Thanks,
Laurent