From 4ad79c874e53ebb7fe3b8ae7ac6c858a2121f415 Mon Sep 17 00:00:00 2001 From: Ben Horgan Date: Fri, 6 Mar 2026 18:27:16 +0000 Subject: [PATCH] arm_mpam: Fix null pointer dereference when restoring bandwidth counters When an MSC supporting memory bandwidth monitoring is brought offline and then online, mpam_restore_mbwu_state() calls __ris_msmon_read() via ipi to restore the configuration of the bandwidth counters. It doesn't care about the value read, mbwu_arg.val, and doesn't set it leading to a null pointer dereference when __ris_msmon_read() adds to it. This results in a kernel oops with a call trace such as: Call trace: __ris_msmon_read+0x19c/0x64c (P) mpam_restore_mbwu_state+0xa0/0xe8 smp_call_on_cpu_callback+0x1c/0x38 process_one_work+0x154/0x4b4 worker_thread+0x188/0x310 kthread+0x11c/0x130 ret_from_fork+0x10/0x20 Provide a local variable for val to avoid __ris_msmon_read() dereferencing a null pointer when adding to val. Fixes: 41e8a14950e1 ("arm_mpam: Track bandwidth counter state for power management") Signed-off-by: Ben Horgan Reviewed-by: James Morse Signed-off-by: James Morse Signed-off-by: Will Deacon --- drivers/resctrl/mpam_devices.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c index 1eebc2602187..0666be6b0e88 100644 --- a/drivers/resctrl/mpam_devices.c +++ b/drivers/resctrl/mpam_devices.c @@ -1428,6 +1428,7 @@ static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid, static int mpam_restore_mbwu_state(void *_ris) { int i; + u64 val; struct mon_read mwbu_arg; struct mpam_msc_ris *ris = _ris; struct mpam_class *class = ris->vmsc->comp->class; @@ -1437,6 +1438,7 @@ static int mpam_restore_mbwu_state(void *_ris) mwbu_arg.ris = ris; mwbu_arg.ctx = &ris->mbwu_state[i].cfg; mwbu_arg.type = mpam_msmon_choose_counter(class); + mwbu_arg.val = &val; __ris_msmon_read(&mwbu_arg); }