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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/6B3A522A-6A5F-4CC9-B268-0C63AA6E07D3@linux.ibm.com

Fixes: 0e0946e22f ("powerpc/papr_scm: Fix leaking nvdimm_events_map elements")
Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220524112353.1718454-1-vaibhav@linux.ibm.com
This commit is contained in:
Vaibhav Jain 2022-05-24 16:53:53 +05:30 committed by Michael Ellerman
parent 1346d00e1b
commit 07bf9431b1
1 changed files with 3 additions and 0 deletions
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3
arch/powerpc/platforms/pseries/papr_scm.c
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@ -465,6 +465,9 @@ static int papr_scm_pmu_check_events(struct papr_scm_priv *p, struct nvdimm_pmu
u32 available_events; u32 available_events;
int index, rc = 0; int index, rc = 0;
if (!p->stat_buffer_len)
return -ENOENT;
available_events = (p->stat_buffer_len - sizeof(struct papr_scm_perf_stats)) available_events = (p->stat_buffer_len - sizeof(struct papr_scm_perf_stats))
/ sizeof(struct papr_scm_perf_stat); / sizeof(struct papr_scm_perf_stat);
if (available_events == 0) if (available_events == 0)