CVE-2024-26687

In the Linux kernel, the following vulnerability has been resolved:
xen/events: close evtchn after mapping cleanup shutdown_pirq and
startup_pirq are not taking the irq_mapping_update_lock because they can’t
due to lock inversion. Both are called with the irq_desc->lock being
taking. The lock order, however, is first irq_mapping_update_lock and then
irq_desc->lock. This opens multiple races: - shutdown_pirq can be
interrupted by a function that allocates an event channel: CPU0 CPU1
shutdown_pirq { xen_evtchn_close(e) __startup_pirq { EVTCHNOP_bind_pirq ->
returns just freed evtchn e set_evtchn_to_irq(e, irq) }
xen_irq_info_cleanup() { set_evtchn_to_irq(e, -1) } } Assume here event
channel e refers here to the same event channel number. After this race the
evtchn_to_irq mapping for e is invalid (-1). - __startup_pirq races with
__unbind_from_irq in a similar way. Because __startup_pirq doesn’t take
irq_mapping_update_lock it can grab the evtchn that __unbind_from_irq is
currently freeing and cleaning up. In this case even though the event
channel is allocated, its mapping can be unset in evtchn_to_irq. The fix is
to first cleanup the mappings and then close the event channel. In this
way, when an event channel gets allocated it’s potential previous
evtchn_to_irq mappings are guaranteed to be unset already. This is also the
reverse order of the allocation where first the event channel is allocated
and then the mappings are setup. On a 5.10 kernel prior to commit
3fcdaf3d7634 (“xen/events: modify internal [un]bind interfaces”), we hit a
BUG like the following during probing of NVMe devices. The issue is that
during nvme_setup_io_queues, pci_free_irq is called for every device which
results in a call to shutdown_pirq. With many nvme devices it’s therefore
likely to hit this race during boot because there will be multiple calls to
shutdown_pirq and startup_pirq are running potentially in parallel.
------------[ cut here ]------------ blkfront: xvda: barrier or flush:
disabled; persistent grants: enabled; indirect descriptors: enabled; bounce
buffer: enabled kernel BUG at drivers/xen/events/events_base.c:499! invalid
opcode: 0000 [#1] SMP PTI CPU: 44 PID: 375 Comm: kworker/u257:23 Not
tainted 5.10.201-191.748.amzn2.x86_64 #1 Hardware name: Xen HVM domU, BIOS
4.11.amazon 08/24/2006 Workqueue: nvme-reset-wq nvme_reset_work RIP:
0010:bind_evtchn_to_cpu+0xdf/0xf0 Code: 5d 41 5e c3 cc cc cc cc 44 89 f7 e8
2b 55 ad ff 49 89 c5 48 85 c0 0f 84 64 ff ff ff 4c 8b 68 30 41 83 fe ff 0f
85 60 ff ff ff <0f> 0b 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 0f 1f
44 00 00 RSP: 0000:ffffc9000d533b08 EFLAGS: 00010046 RAX: 0000000000000000
RBX: 0000000000000000 RCX: 0000000000000006 RDX: 0000000000000028 RSI:
00000000ffffffff RDI: 00000000ffffffff RBP: ffff888107419680 R08:
0000000000000000 R09: ffffffff82d72b00 R10: 0000000000000000 R11:
0000000000000000 R12: 00000000000001ed R13: 0000000000000000 R14:
00000000ffffffff R15: 0000000000000002 FS: 0000000000000000(0000)
GS:ffff88bc8b500000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000
CR0: 0000000080050033 CR2: 0000000000000000 CR3: 0000000002610001 CR4:
00000000001706e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400 Call Trace: ? show_trace_log_lvl+0x1c1/0x2d9 ?
show_trace_log_lvl+0x1c1/0x2d9 ? set_affinity_irq+0xdc/0x1c0 ?
__die_body.cold+0x8/0xd ? die+0x2b/0x50 ? do_trap+0x90/0x110 ?
bind_evtchn_to_cpu+0xdf/0xf0 ? do_error_trap+0x65/0x80 ?
bind_evtchn_to_cpu+0xdf/0xf0 ? exc_invalid_op+0x4e/0x70 ?
bind_evtchn_to_cpu+0xdf/0xf0 ? asm_exc_invalid_op+0x12/0x20 ?
bind_evtchn_to_cpu+0xdf/0x —truncated—