Unknown
CVE-2024-46797
CVE-2024-46797
Description
In the Linux kernel, the following vulnerability has been resolved:
powerpc/qspinlock: Fix deadlock in MCS queue
If an interrupt occurs in queued_spin_lock_slowpath() after we increment
qnodesp->count and before node->lock is initialized, another CPU might
see stale lock values in get_tail_qnode(). If the stale lock value happens
to match the lock on that CPU, then we write to the “next” pointer of
the wrong qnode. This causes a deadlock as the former CPU, once it becomes
the head of the MCS queue, will spin indefinitely until it’s “next” pointer
is set by its successor in the queue.
Running stress-ng on a 16 core (16EC/16VP) shared LPAR, results in
occasional 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/0x2ec
The following code flow illustrates how the deadlock occurs.
For the sake of brevity, assume that both locks (A and B) are
contended 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—-
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