Overview

In the Linux kernel, the following vulnerability has been resolved:

powerpc/imc-pmu: Fix use of mutex in IRQs disabled section

Current imc-pmu code triggers a WARNING with CONFIG_DEBUG_ATOMIC_SLEEP and CONFIG_PROVE_LOCKING enabled, while running a thread_imc event.

Command to trigger the warning:

perf stat -e thread_imc/CPM_CS_FROM_L4_MEM_X_DPTEG/ sleep 5

Performance counter stats for 'sleep 5':

               0      thread_imc/CPM_CS_FROM_L4_MEM_X_DPTEG/

     5.002117947 seconds time elapsed

     0.000131000 seconds user
     0.001063000 seconds sys

Below is snippet of the warning in dmesg:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 2869, name: perf-exec preempt_count: 2, expected: 0 4 locks held by perf-exec/2869: #0: c00000004325c540 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: bprm_execve+0x64/0xa90 #1: c00000004325c5d8 (&sig->exec_update_lock){++++}-{3:3}, at: begin_new_exec+0x460/0xef0 #2: c0000003fa99d4e0 (&cpuctx_lock){-...}-{2:2}, at: perf_event_exec+0x290/0x510 #3: c000000017ab8418 (&ctx->lock){....}-{2:2}, at: perf_event_exec+0x29c/0x510 irq event stamp: 4806 hardirqs last enabled at (4805): [<c000000000f65b94>] _raw_spin_unlock_irqrestore+0x94/0xd0 hardirqs last disabled at (4806): [<c0000000003fae44>] perf_event_exec+0x394/0x510 softirqs last enabled at (0): [<c00000000013c404>] copy_process+0xc34/0x1ff0 softirqs last disabled at (0): [<0000000000000000>] 0x0 CPU: 36 PID: 2869 Comm: perf-exec Not tainted 6.2.0-rc2-00011-g1247637727f2 #61 Hardware name: 8375-42A POWER9 0x4e1202 opal:v7.0-16-g9b85f7d961 PowerNV Call Trace: dump_stack_lvl+0x98/0xe0 (unreliable) __might_resched+0x2f8/0x310 __mutex_lock+0x6c/0x13f0 thread_imc_event_add+0xf4/0x1b0 event_sched_in+0xe0/0x210 merge_sched_in+0x1f0/0x600 visit_groups_merge.isra.92.constprop.166+0x2bc/0x6c0 ctx_flexible_sched_in+0xcc/0x140 ctx_sched_in+0x20c/0x2a0 ctx_resched+0x104/0x1c0 perf_event_exec+0x340/0x510 begin_new_exec+0x730/0xef0 load_elf_binary+0x3f8/0x1e10 ... do not call blocking ops when !TASK_RUNNING; state=2001 set at [<00000000fd63e7cf>] do_nanosleep+0x60/0x1a0 WARNING: CPU: 36 PID: 2869 at kernel/sched/core.c:9912 __might_sleep+0x9c/0xb0 CPU: 36 PID: 2869 Comm: sleep Tainted: G W 6.2.0-rc2-00011-g1247637727f2 #61 Hardware name: 8375-42A POWER9 0x4e1202 opal:v7.0-16-g9b85f7d961 PowerNV NIP: c000000000194a1c LR: c000000000194a18 CTR: c000000000a78670 REGS: c00000004d2134e0 TRAP: 0700 Tainted: G W (6.2.0-rc2-00011-g1247637727f2) MSR: 9000000000021033 <SF,HV,ME,IR,DR,RI,LE> CR: 48002824 XER: 00000000 CFAR: c00000000013fb64 IRQMASK: 1

The above warning triggered because the current imc-pmu code uses mutex lock in interrupt disabled sections. The function mutex_lock() internally calls __might_resched(), which will check if IRQs are disabled and in case IRQs are disabled, it will trigger the warning.

Fix the issue by changing the mutex lock to spinlock.

[mpe: Fix comments, trim oops in change log, add reported-by tags]

Affected

• Linux >= 8f95faaac56c18b32d0e23ace55417a440abdb7e < d0c6d2a31026102d4738b47a610bed4401b9834f
• Linux >= 8f95faaac56c18b32d0e23ace55417a440abdb7e < 8cbeb60320ac45a8240b561c8ef466b86c34dedc
• Linux >= 8f95faaac56c18b32d0e23ace55417a440abdb7e < a90d339f1f66be4a946769b565668e2bd0686dfa
• Linux >= 8f95faaac56c18b32d0e23ace55417a440abdb7e < 424bcb570cb320d1d15238cd4c933522b90f78fa
• Linux >= 8f95faaac56c18b32d0e23ace55417a440abdb7e < 76d588dddc459fefa1da96e0a081a397c5c8e216
• Linux 4.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.