From: Vaibhav Jain vaibhav@linux.ibm.com
[ Upstream commit 07bf9431b1590d1cd7a8d62075d0b50b073f0495 ]
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.c...
Fixes: 0e0946e22f3665d2732 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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)