mm/vmalloc: combine all TLB flush operations of KASAN shadow virtual address into one operation
CVE: CVE-2024-56559
Component: kernel
Severity: Low
CVSS v3: 4.4/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
Release date: 2024-12-27T00:00:00+00:00

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:
 <IRQ>
 ? 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
 </IRQ>
 <TASK>
 ? 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
 </TASK>

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---

Statement: The affected code not introduced yet in Red Hat Enterprise Linux. The bug happens for specific conditions (when compiling debug kernel for many cores platform). The security impact is limited.

Remediation: