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Subject[PATCH AUTOSEL for 4.15 185/189] powerpc/powernv: IMC fix out of bounds memory access at shutdown
From: Nicholas Piggin <>

[ Upstream commit e7bde88cdb4f0e432398a7d29ca2a15d2c18952a ]

The OPAL IMC driver's shutdown handler disables nest PMU counters by
walking nodes and taking the first CPU out of their cpumask, which is
used to index into the paca (get_hard_smp_processor_id()). This does
not always do the right thing, and in particular for CPU-less nodes it
returns NR_CPUS and that overruns the paca and dereferences random

Fix it by being more careful about checking returned CPU, and only
using online CPUs. It's not clear this shutdown code makes sense after
commit 885dcd709b ("powerpc/perf: Add nest IMC PMU support"), but this
should not make things worse

Currently the bug causes us to call OPAL with a junk CPU number. A
separate patch in development to change the way pacas are allocated
escalates this bug into a crash:

Unable to handle kernel paging request for data at address 0x2a21af1eeb000076
Faulting instruction address: 0xc0000000000a5468
Oops: Kernel access of bad area, sig: 11 [#1]
NIP opal_imc_counters_shutdown+0x148/0x1d0
LR opal_imc_counters_shutdown+0x134/0x1d0
Call Trace:
opal_imc_counters_shutdown+0x134/0x1d0 (unreliable)

Signed-off-by: Nicholas Piggin <>
Signed-off-by: Michael Ellerman <>
Signed-off-by: Sasha Levin <>
arch/powerpc/platforms/powernv/opal-imc.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/opal-imc.c b/arch/powerpc/platforms/powernv/opal-imc.c
index 465ea105b771..5f27854b57aa 100644
--- a/arch/powerpc/platforms/powernv/opal-imc.c
+++ b/arch/powerpc/platforms/powernv/opal-imc.c
@@ -126,9 +126,11 @@ static void disable_nest_pmu_counters(void)
const struct cpumask *l_cpumask;

- for_each_online_node(nid) {
+ for_each_node_with_cpus(nid) {
l_cpumask = cpumask_of_node(nid);
- cpu = cpumask_first(l_cpumask);
+ cpu = cpumask_first_and(l_cpumask, cpu_online_mask);
+ if (cpu >= nr_cpu_ids)
+ continue;
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