powerpc/papr_scm: don't requests stats with '0' sized stats buffer

JIRA: https://issues.redhat.com/browse/RHEL-81000

CVE: CVE-2022-49353

commit 07bf943
Author: Vaibhav Jain <[email protected]>
Date:   Tue May 24 16:53:53 2022 +0530

    powerpc/papr_scm: don't requests stats with '0' sized stats buffer

    Sachin reported [1] that on a POWER-10 lpar he is seeing a kernel panic being
    reported with vPMEM when papr_scm probe is being called. The panic is of the
    form below and is observed only with following option disabled(profile) for the
    said LPAR 'Enable Performance Information Collection' in the HMC:

     Kernel attempted to write user page (1c) - exploit attempt? (uid: 0)
     BUG: Kernel NULL pointer dereference on write at 0x0000001c
     Faulting instruction address: 0xc008000001b90844
     Oops: Kernel access of bad area, sig: 11 [#1]
    <snip>
     NIP [c008000001b90844] drc_pmem_query_stats+0x5c/0x270 [papr_scm]
     LR [c008000001b92794] papr_scm_probe+0x2ac/0x6ec [papr_scm]
     Call Trace:
           0xc00000000941bca0 (unreliable)
           papr_scm_probe+0x2ac/0x6ec [papr_scm]
           platform_probe+0x98/0x150
           really_probe+0xfc/0x510
           __driver_probe_device+0x17c/0x230
    <snip>
     ---[ end trace 0000000000000000 ]---
     Kernel panic - not syncing: Fatal exception

    On investigation looks like this panic was caused due to a 'stat_buffer' of
    size==0 being provided to drc_pmem_query_stats() to fetch all performance
    stats-ids of an NVDIMM. However drc_pmem_query_stats() shouldn't have been called
    since the vPMEM NVDIMM doesn't support and performance stat-id's. This was caused
    due to missing check for 'p->stat_buffer_len' at the beginning of
    papr_scm_pmu_check_events() which indicates that the NVDIMM doesn't support
    performance-stats.

    Fix this by introducing the check for 'p->stat_buffer_len' at the beginning of
    papr_scm_pmu_check_events().

    [1] https://lore.kernel.org/all/[email protected]

    Fixes: 0e0946e ("powerpc/papr_scm: Fix leaking nvdimm_events_map elements")
    Reported-by: Sachin Sant <[email protected]>
    Signed-off-by: Vaibhav Jain <[email protected]>
    Tested-by: Sachin Sant <[email protected]>
    Signed-off-by: Michael Ellerman <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]

Signed-off-by: Mamatha Inamdar <[email protected]>

Author: Mamatha Inamdar

arch/powerpc/platforms/pseries/papr_scm.c

@@ -465,6 +465,9 @@ static int papr_scm_pmu_check_events(struct papr_scm_priv *p, struct nvdimm_pmu
 	u32 available_events;
 	int index, rc = 0;
 
+	if (!p->stat_buffer_len)
+		return -ENOENT;
+
 	available_events = (p->stat_buffer_len  - sizeof(struct papr_scm_perf_stats))
 			/ sizeof(struct papr_scm_perf_stat);
 	if (available_events == 0)