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-b268-0c63aa6e0...@linux.ibm.com
Fixes: 0e0946e22f3665d2732 ("powerpc/papr_scm: Fix leaking nvdimm_events_map
elements")
Reported-by: Sachin Sant <sach...@linux.ibm.com>
Signed-off-by: Vaibhav Jain <vaib...@linux.ibm.com>
---
arch/powerpc/platforms/pseries/papr_scm.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/powerpc/platforms/pseries/papr_scm.c
b/arch/powerpc/platforms/pseries/papr_scm.c
index 181b855b3050..82cae08976bc 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/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)
--
2.35.1
