Re: [PATCH] spapr: Fix buffer overflow in spapr_numa_associativity_init()

[Daniel Henrique Barboza]

On 12/18/20 10:53 AM, Greg Kurz wrote:

Running a guest with 128 NUMA nodes crashes QEMU:

../../util/error.c:59: error_setv: Assertion `*errp == NULL' failed.

The crash happens when setting the FWNMI migration blocker:

2861        if (spapr_get_cap(spapr, SPAPR_CAP_FWNMI) == SPAPR_CAP_ON) {
2862            /* Create the error string for live migration blocker */
2863            error_setg(&spapr->fwnmi_migration_blocker,
2864                "A machine check is being handled during migration. The 
handler"
2865                "may run and log hardware error on the destination");
2866        }

Inspection reveals that papr->fwnmi_migration_blocker isn't NULL:

(gdb) p spapr->fwnmi_migration_blocker
$1 = (Error *) 0x8000000004000000

Since this is the only place where papr->fwnmi_migration_blocker is
set, this means someone wrote there in our back. Further analysis
points to spapr_numa_associativity_init(), especially the part
that initializes the associative arrays for NVLink GPUs:

     max_nodes_with_gpus = nb_numa_nodes + NVGPU_MAX_NUM;

ie. max_nodes_with_gpus = 128 + 6, but the array isn't sized to
accommodate the 6 extra nodes:

#define MAX_NODES 128

struct SpaprMachineState {
     .
     .
     .
     uint32_t numa_assoc_array[MAX_NODES][NUMA_ASSOC_SIZE];

     Error *fwnmi_migration_blocker;
};

and the following loops happily overwrite spapr->fwnmi_migration_blocker,
and probably more:

     for (i = nb_numa_nodes; i < max_nodes_with_gpus; i++) {
         spapr->numa_assoc_array[i][0] = cpu_to_be32(MAX_DISTANCE_REF_POINTS);

         for (j = 1; j < MAX_DISTANCE_REF_POINTS; j++) {
             uint32_t gpu_assoc = smc->pre_5_1_assoc_refpoints ?
                                  SPAPR_GPU_NUMA_ID : cpu_to_be32(i);
             spapr->numa_assoc_array[i][j] = gpu_assoc;
         }

         spapr->numa_assoc_array[i][MAX_DISTANCE_REF_POINTS] = cpu_to_be32(i);
     }

Fix the size of the array. This requires "hw/ppc/spapr.h" to see
NVGPU_MAX_NUM. Including "hw/pci-host/spapr.h" introduces a
circular dependency that breaks the build, so this moves the
definition of NVGPU_MAX_NUM to "hw/ppc/spapr.h" instead.

Reported-by: Min Deng <md...@redhat.com>
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1908693
Fixes: dd7e1d7ae431 ("spapr_numa: move NVLink2 associativity handling to 
spapr_numa.c")
Cc: danielhb...@gmail.com
Signed-off-by: Greg Kurz <gr...@kaod.org>
---

Good catch. Thanks for fixing it!

Reviewed-by: Daniel Henrique Barboza <danielhb...@gmail.com>

  include/hw/pci-host/spapr.h |    2 --
  include/hw/ppc/spapr.h      |    5 ++++-
  2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/hw/pci-host/spapr.h b/include/hw/pci-host/spapr.h
index 4f58f0223b56..bd014823a933 100644
--- a/include/hw/pci-host/spapr.h
+++ b/include/hw/pci-host/spapr.h
@@ -115,8 +115,6 @@ struct SpaprPhbState {
  #define SPAPR_PCI_NV2RAM64_WIN_BASE  SPAPR_PCI_LIMIT
  #define SPAPR_PCI_NV2RAM64_WIN_SIZE  (2 * TiB) /* For up to 6 GPUs 256GB each 
*/

-/* Max number of these GPUsper a physical box */

-#define NVGPU_MAX_NUM                6
  /* Max number of NVLinks per GPU in any physical box */
  #define NVGPU_MAX_LINKS              3

diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h

index 06a5b4259f20..1cc19575f548 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -112,6 +112,9 @@ typedef enum {
  #define NUMA_ASSOC_SIZE            (MAX_DISTANCE_REF_POINTS + 1)
  #define VCPU_ASSOC_SIZE            (NUMA_ASSOC_SIZE + 1)

+/* Max number of these GPUsper a physical box */

+#define NVGPU_MAX_NUM                6
+
  typedef struct SpaprCapabilities SpaprCapabilities;
  struct SpaprCapabilities {
      uint8_t caps[SPAPR_CAP_NUM];
@@ -240,7 +243,7 @@ struct SpaprMachineState {
      unsigned gpu_numa_id;
      SpaprTpmProxy *tpm_proxy;

- uint32_t numa_assoc_array[MAX_NODES][NUMA_ASSOC_SIZE];

+    uint32_t numa_assoc_array[MAX_NODES + NVGPU_MAX_NUM][NUMA_ASSOC_SIZE];

Error *fwnmi_migration_blocker;

  };