N/A - CVE-2024-56559

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

mm/vmalloc: combine all TLB flush operations of KASAN shadow virtual address into one operation

When compiling kernel source 'make -j $(nproc)' with the up-and-running KASAN-enabled kernel on a 256-core machine, the following soft lockup is shown:

watchdog: BUG: soft lockup - CPU#28 stuck for 22s! [kworker/28:1:1760] CPU: 28 PID: 1760 Comm: kworker/28:1 Kdump: loaded Not tainted 6.10.0-rc5 #95 Workqueue: events drain_vmap_area_work RIP: 0010:smp_call_function_many_cond+0x1d8/0xbb0 Code: 38 c8 7c 08 84 c9 0f 85 49 08 00 00 8b 45 08 a8 01 74 2e 48 89 f1 49 89 f7 48 c1 e9 03 41 83 e7 07 4c 01 e9 41 83 c7 03 f3 90 <0f> b6 01 41 38 c7 7c 08 84 c0 0f 85 d4 06 00 00 8b 45 08 a8 01 75 RSP: 0018:ffffc9000cb3fb60 EFLAGS: 00000202 RAX: 0000000000000011 RBX: ffff8883bc4469c0 RCX: ffffed10776e9949 RDX: 0000000000000002 RSI: ffff8883bb74ca48 RDI: ffffffff8434dc50 RBP: ffff8883bb74ca40 R08: ffff888103585dc0 R09: ffff8884533a1800 R10: 0000000000000004 R11: ffffffffffffffff R12: ffffed1077888d39 R13: dffffc0000000000 R14: ffffed1077888d38 R15: 0000000000000003 FS: 0000000000000000(0000) GS:ffff8883bc400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005577b5c8d158 CR3: 0000000004850000 CR4: 0000000000350ef0 Call Trace:

? watchdog_timer_fn+0x2cd/0x390
? __pfx_watchdog_timer_fn+0x10/0x10
? __hrtimer_run_queues+0x300/0x6d0
? sched_clock_cpu+0x69/0x4e0
? __pfx___hrtimer_run_queues+0x10/0x10
? srso_return_thunk+0x5/0x5f
? ktime_get_update_offsets_now+0x7f/0x2a0
? srso_return_thunk+0x5/0x5f
? srso_return_thunk+0x5/0x5f
? hrtimer_interrupt+0x2ca/0x760
? __sysvec_apic_timer_interrupt+0x8c/0x2b0
? sysvec_apic_timer_interrupt+0x6a/0x90


? asm_sysvec_apic_timer_interrupt+0x16/0x20
? smp_call_function_many_cond+0x1d8/0xbb0
? __pfx_do_kernel_range_flush+0x10/0x10
on_each_cpu_cond_mask+0x20/0x40
flush_tlb_kernel_range+0x19b/0x250
? srso_return_thunk+0x5/0x5f
? kasan_release_vmalloc+0xa7/0xc0
purge_vmap_node+0x357/0x820
? __pfx_purge_vmap_node+0x10/0x10
__purge_vmap_area_lazy+0x5b8/0xa10
drain_vmap_area_work+0x21/0x30
process_one_work+0x661/0x10b0
worker_thread+0x844/0x10e0
? srso_return_thunk+0x5/0x5f
? __kthread_parkme+0x82/0x140
? __pfx_worker_thread+0x10/0x10
kthread+0x2a5/0x370
? __pfx_kthread+0x10/0x10
ret_from_fork+0x30/0x70
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30

Debugging Analysis:

1. The following ftrace log shows that the lockup CPU spends too much
time iterating vmap_nodes and flushing TLB when purging vm_area
structures. (Some info is trimmed).

kworker: funcgraph_entry: | drain_vmap_area_work() {
kworker: funcgraph_entry: | mutex_lock() {
kworker: funcgraph_entry: 1.092 us | __cond_resched();
kworker: funcgraph_exit: 3.306 us | }
... ...
kworker: funcgraph_entry: | flush_tlb_kernel_range() {
... ...
kworker: funcgraph_exit: # 7533.649 us | }
... ...
kworker: funcgraph_entry: 2.344 us | mutex_unlock();
kworker: funcgraph_exit: $ 23871554 us | }

The drain_vmap_area_work() spends over 23 seconds.

There are 2805 flush_tlb_kernel_range() calls in the ftrace log.
* One is called in __purge_vmap_area_lazy().
* Others are called by purge_vmap_node->kasan_release_vmalloc.
purge_vmap_node() iteratively releases kasan vmalloc
allocations and flushes TLB for each vmap_area.
- [Rough calculation] Each flush_tlb_kernel_range() runs
about 7.5ms.
-- 2804 * 7.5ms = 21.03 seconds.
-- That's why a soft lock is triggered.

2. Extending the soft lockup time can work around the issue (For example,
# echo ---truncated---