摘要:

In the Linux kernel, the following vulnerability has been resolved:powerpc/qspinlock: Fix deadlock in MCS queueIf an interrupt occurs in queued_spin_lock_slowpath() after we incrementqnodesp->count and before node->lock is initialized, another CPU mightsee stale lock values in get_tail_qnode(). If the stale lock value happensto match the lock on that CPU, then we write to the next pointer ofthe wrong qnode. This causes a deadlock as the former CPU, once it becomesthe head of the MCS queue, will spin indefinitely until it s next pointeris set by its successor in the queue.Running stress-ng on a 16 core (16EC/16VP) shared LPAR, results inoccasional lockups similar to the following: $ stress-ng --all 128 --vm-bytes 80% --aggressive --maximize --oomable --verify --syslog --metrics --times --timeout 5m watchdog: CPU 15 Hard LOCKUP ...... NIP [c0000000000b78f4] queued_spin_lock_slowpath+0x1184/0x1490 LR [c000000001037c5c] _raw_spin_lock+0x6c/0x90 Call Trace: 0xc000002cfffa3bf0 (unreliable) _raw_spin_lock+0x6c/0x90 raw_spin_rq_lock_nested.part.135+0x4c/0xd0 sched_ttwu_pending+0x60/0x1f0 __flush_smp_call_function_queue+0x1dc/0x670 smp_ipi_demux_relaxed+0xa4/0x100 xive_muxed_ipi_action+0x20/0x40 __handle_irq_event_percpu+0x80/0x240 handle_irq_event_percpu+0x2c/0x80 handle_percpu_irq+0x84/0xd0 generic_handle_irq+0x54/0x80 __do_irq+0xac/0x210 __do_IRQ+0x74/0xd0 0x0 do_IRQ+0x8c/0x170 hardware_interrupt_common_virt+0x29c/0x2a0 --- interrupt: 500 at queued_spin_lock_slowpath+0x4b8/0x1490 ...... NIP [c0000000000b6c28] queued_spin_lock_slowpath+0x4b8/0x1490 LR [c000000001037c5c] _raw_spin_lock+0x6c/0x90 --- interrupt: 500 0xc0000029c1a41d00 (unreliable) _raw_spin_lock+0x6c/0x90 futex_wake+0x100/0x260 do_futex+0x21c/0x2a0 sys_futex+0x98/0x270 system_call_exception+0x14c/0x2f0 system_call_vectored_common+0x15c/0x2ecThe following code flow illustrates how the deadlock occurs.For the sake of brevity, assume that both locks (A and B) arecontended and we call the queued_spin_lock_slowpath() function. CPU0 CPU1 ---- ---- spin_lock_irqsave(A) | spin_unlock_irqrestore(A) | spin_lock(B) | | | ▼ | id = qnodesp->count++; | (Note that nodes[0].lock == A) | | | ▼ | Interrupt | (happens before nodes[0].lock = B ) | | | ▼ | spin_lock_irqsave(A) | | | ▼ | id = qnodesp->count++ | nodes[1].lock = A | | | ▼ | Tail of MCS queue | | spin_lock_irqsave(A) ▼ | Head of MCS queue ▼ | CPU0 is previous tail ▼ | Spin indefinitely ▼ (until nodes[1].next != NULL ) prev = get_tail_qnode(A, CPU0) | ▼ prev == &qnodes[CPU0].nodes[0] (as qnodes---truncated---

安全等级: Low

公告ID: KylinSec-SA-2024-3913

发布日期: 2024年10月12日

关联CVE: CVE-2024-46797