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Re: [PATCH v2 2/2] spapr/nvram: Error out if NVRAM cannot contain all -p

From: John Snow
Subject: Re: [PATCH v2 2/2] spapr/nvram: Error out if NVRAM cannot contain all -prom-env data
Date: Wed, 12 Aug 2020 13:18:40 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 8/12/20 1:08 PM, 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 true, in order to know the required size and fail
gracefully if it's too small.

Reported-by: John Snow <jsnow@redhat.com>
Signed-off-by: Greg Kurz <groug@kaod.org>

Fixes: 61f20b9dc5b7
RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1867739

Thanks :)

  hw/nvram/spapr_nvram.c |   15 +++++++++++++++
  1 file changed, 15 insertions(+)

diff --git a/hw/nvram/spapr_nvram.c b/hw/nvram/spapr_nvram.c
index 992b818d34e7..c29d797ae1f0 100644
--- a/hw/nvram/spapr_nvram.c
+++ b/hw/nvram/spapr_nvram.c
@@ -145,6 +145,7 @@ static void rtas_nvram_store(PowerPCCPU *cpu, 
SpaprMachineState *spapr,
static void spapr_nvram_realize(SpaprVioDevice *dev, Error **errp)
+    ERRP_GUARD();
      SpaprNvram *nvram = VIO_SPAPR_NVRAM(dev);
      int ret;
@@ -187,6 +188,20 @@ static void spapr_nvram_realize(SpaprVioDevice *dev, Error **errp)
      } else if (nb_prom_envs > 0) {
+        int len = chrp_nvram_create_system_partition(nvram->buf,
+                                                     MIN_NVRAM_SIZE / 4,
+                                                     true);
+        /* Check the partition is large enough for all the -prom-env data */
+        if (nvram->size < len) {
+            error_setg(errp, "-prom-env data requires %d bytes but spapr-nvram 
+                       "is only %d bytes in size", len, nvram->size);
+            error_append_hint(errp,
+                              "Try to pass %d less bytes to -prom-env.\n",
+                              len - nvram->size);
+            return;
+        }
          /* Create a system partition to pass the -prom-env variables */
          chrp_nvram_create_system_partition(nvram->buf, MIN_NVRAM_SIZE / 4,

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