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

[Greg Kurz]

On Tue, 11 Aug 2020 19:27:50 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> On 11/08/2020 18:36, Greg Kurz wrote:
> > 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 ?
> 
> It's not true for all the arguments: take for instance the blockdev, the
> chardev, the netdev, vnc,  ... I think it's true only for parameters
> that define the devices, the machine. And until now for prom-env it was
> not the case, look at the migration-test test case.
> 

        arch_source = g_strdup_printf("-nodefaults "
                                      "-prom-env 'use-nvramrc?=true' -prom-env "
                                      "'nvramrc=hex .\" _\" begin %x %x "
                                      "do i c@ 1 + i c! 1000 +loop .\" B\" 0 "
                                      "until'", end_address, start_address);
        arch_target = g_strdup("");

Ok, my bad... I should have run that before posting.

So, I'll go the other way around and have QEMU to error out if the -prom-env
data doesn't fit in the default size (64 Kib).

> Thanks,
> Laurent
> 
>