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

[Daniel Henrique Barboza <danielhb413@gmail.com>]

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 <mdeng@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: danielhb413@gmail.com
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---


Good catch. Thanks for fixing it!

Reviewed-by: Daniel Henrique Barboza <danielhb413@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;
>   };
> 
> 
>