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

s390/fpu: Fix false-positive kmsan report in fpu_vstl()

A false-positive kmsan report is detected when running ping command.

An inline assembly instruction 'vstl' can write varied amount of bytes
depending on value of 'index' argument. If 'index' > 0, 'vstl' writes
at least 2 bytes.

clang generates kmsan write helper call depending on inline assembly
constraints. Constraints are evaluated compile-time, but value of
'index' argument is known only at runtime.

clang currently generates call to __msan_instrument_asm_store with 1 byte
as size. Manually call kmsan function to indicate correct amount of bytes
written and fix false-positive report.

This change fixes following kmsan reports:

[ 36.563119] =====================================================
[ 36.563594] BUG: KMSAN: uninit-value in virtqueue_add+0x35c6/0x7c70
[ 36.563852] virtqueue_add+0x35c6/0x7c70
[ 36.564016] virtqueue_add_outbuf+0xa0/0xb0
[ 36.564266] start_xmit+0x288c/0x4a20
[ 36.564460] dev_hard_start_xmit+0x302/0x900
[ 36.564649] sch_direct_xmit+0x340/0xea0
[ 36.564894] __dev_queue_xmit+0x2e94/0x59b0
[ 36.565058] neigh_resolve_output+0x936/0xb40
[ 36.565278] __neigh_update+0x2f66/0x3a60
[ 36.565499] neigh_update+0x52/0x60
[ 36.565683] arp_process+0x1588/0x2de0
[ 36.565916] NF_HOOK+0x1da/0x240
[ 36.566087] arp_rcv+0x3e4/0x6e0
[ 36.566306] __netif_receive_skb_list_core+0x1374/0x15a0
[ 36.566527] netif_receive_skb_list_internal+0x1116/0x17d0
[ 36.566710] napi_complete_done+0x376/0x740
[ 36.566918] virtnet_poll+0x1bae/0x2910
[ 36.567130] __napi_poll+0xf4/0x830
[ 36.567294] net_rx_action+0x97c/0x1ed0
[ 36.567556] handle_softirqs+0x306/0xe10
[ 36.567731] irq_exit_rcu+0x14c/0x2e0
[ 36.567910] do_io_irq+0xd4/0x120
[ 36.568139] io_int_handler+0xc2/0xe8
[ 36.568299] arch_cpu_idle+0xb0/0xc0
[ 36.568540] arch_cpu_idle+0x76/0xc0
[ 36.568726] default_idle_call+0x40/0x70
[ 36.568953] do_idle+0x1d6/0x390
[ 36.569486] cpu_startup_entry+0x9a/0xb0
[ 36.569745] rest_init+0x1ea/0x290
[ 36.570029] start_kernel+0x95e/0xb90
[ 36.570348] startup_continue+0x2e/0x40
[ 36.570703]
[ 36.570798] Uninit was created at:
[ 36.571002] kmem_cache_alloc_node_noprof+0x9e8/0x10e0
[ 36.571261] kmalloc_reserve+0x12a/0x470
[ 36.571553] __alloc_skb+0x310/0x860
[ 36.571844] __ip_append_data+0x483e/0x6a30
[ 36.572170] ip_append_data+0x11c/0x1e0
[ 36.572477] raw_sendmsg+0x1c8c/0x2180
[ 36.572818] inet_sendmsg+0xe6/0x190
[ 36.573142] __sys_sendto+0x55e/0x8e0
[ 36.573392] __s390x_sys_socketcall+0x19ae/0x2ba0
[ 36.573571] __do_syscall+0x12e/0x240
[ 36.573823] system_call+0x6e/0x90
[ 36.573976]
[ 36.574017] Byte 35 of 98 is uninitialized
[ 36.574082] Memory access of size 98 starts at 0000000007aa0012
[ 36.574218]
[ 36.574325] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G B N 6.17.0-dirty #16 NONE
[ 36.574541] Tainted: [B]=BAD_PAGE, [N]=TEST
[ 36.574617] Hardware name: IBM 3931 A01 703 (KVM/Linux)
[ 36.574755] =====================================================

[ 63.532541] =====================================================
[ 63.533639] BUG: KMSAN: uninit-value in virtqueue_add+0x35c6/0x7c70
[ 63.533989] virtqueue_add+0x35c6/0x7c70
[ 63.534940] virtqueue_add_outbuf+0xa0/0xb0
[ 63.535861] start_xmit+0x288c/0x4a20
[ 63.536708] dev_hard_start_xmit+0x302/0x900
[ 63.537020] sch_direct_xmit+0x340/0xea0
[ 63.537997] __dev_queue_xmit+0x2e94/0x59b0
[ 63.538819] neigh_resolve_output+0x936/0xb40
[ 63.539793] ip_finish_output2+0x1ee2/0x2200
[ 63.540784] __ip_finish_output+0x272/0x7a0
[ 63.541765] ip_finish_output+0x4e/0x5e0
[ 63.542791] ip_output+0x166/0x410
[ 63.543771] ip_push_pending_frames+0x1a2/0x470
[ 63.544753] raw_sendmsg+0x1f06/0x2180
[ 63.545033] inet_sendmsg+0xe6/0x190
[ 63.546006] __sys_sendto+0x55e/0x8e0
---truncated---
Published: 2026-01-05
Score: 5.5 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8094-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8094-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8094-3 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-8094-4 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8094-5 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-8152-1 Linux kernel (OEM) vulnerabilities
History

Mon, 05 Jan 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Low

Mon, 05 Jan 2026 10:00:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: s390/fpu: Fix false-positive kmsan report in fpu_vstl() A false-positive kmsan report is detected when running ping command. An inline assembly instruction 'vstl' can write varied amount of bytes depending on value of 'index' argument. If 'index' > 0, 'vstl' writes at least 2 bytes. clang generates kmsan write helper call depending on inline assembly constraints. Constraints are evaluated compile-time, but value of 'index' argument is known only at runtime. clang currently generates call to __msan_instrument_asm_store with 1 byte as size. Manually call kmsan function to indicate correct amount of bytes written and fix false-positive report. This change fixes following kmsan reports: [ 36.563119] ===================================================== [ 36.563594] BUG: KMSAN: uninit-value in virtqueue_add+0x35c6/0x7c70 [ 36.563852] virtqueue_add+0x35c6/0x7c70 [ 36.564016] virtqueue_add_outbuf+0xa0/0xb0 [ 36.564266] start_xmit+0x288c/0x4a20 [ 36.564460] dev_hard_start_xmit+0x302/0x900 [ 36.564649] sch_direct_xmit+0x340/0xea0 [ 36.564894] __dev_queue_xmit+0x2e94/0x59b0 [ 36.565058] neigh_resolve_output+0x936/0xb40 [ 36.565278] __neigh_update+0x2f66/0x3a60 [ 36.565499] neigh_update+0x52/0x60 [ 36.565683] arp_process+0x1588/0x2de0 [ 36.565916] NF_HOOK+0x1da/0x240 [ 36.566087] arp_rcv+0x3e4/0x6e0 [ 36.566306] __netif_receive_skb_list_core+0x1374/0x15a0 [ 36.566527] netif_receive_skb_list_internal+0x1116/0x17d0 [ 36.566710] napi_complete_done+0x376/0x740 [ 36.566918] virtnet_poll+0x1bae/0x2910 [ 36.567130] __napi_poll+0xf4/0x830 [ 36.567294] net_rx_action+0x97c/0x1ed0 [ 36.567556] handle_softirqs+0x306/0xe10 [ 36.567731] irq_exit_rcu+0x14c/0x2e0 [ 36.567910] do_io_irq+0xd4/0x120 [ 36.568139] io_int_handler+0xc2/0xe8 [ 36.568299] arch_cpu_idle+0xb0/0xc0 [ 36.568540] arch_cpu_idle+0x76/0xc0 [ 36.568726] default_idle_call+0x40/0x70 [ 36.568953] do_idle+0x1d6/0x390 [ 36.569486] cpu_startup_entry+0x9a/0xb0 [ 36.569745] rest_init+0x1ea/0x290 [ 36.570029] start_kernel+0x95e/0xb90 [ 36.570348] startup_continue+0x2e/0x40 [ 36.570703] [ 36.570798] Uninit was created at: [ 36.571002] kmem_cache_alloc_node_noprof+0x9e8/0x10e0 [ 36.571261] kmalloc_reserve+0x12a/0x470 [ 36.571553] __alloc_skb+0x310/0x860 [ 36.571844] __ip_append_data+0x483e/0x6a30 [ 36.572170] ip_append_data+0x11c/0x1e0 [ 36.572477] raw_sendmsg+0x1c8c/0x2180 [ 36.572818] inet_sendmsg+0xe6/0x190 [ 36.573142] __sys_sendto+0x55e/0x8e0 [ 36.573392] __s390x_sys_socketcall+0x19ae/0x2ba0 [ 36.573571] __do_syscall+0x12e/0x240 [ 36.573823] system_call+0x6e/0x90 [ 36.573976] [ 36.574017] Byte 35 of 98 is uninitialized [ 36.574082] Memory access of size 98 starts at 0000000007aa0012 [ 36.574218] [ 36.574325] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G B N 6.17.0-dirty #16 NONE [ 36.574541] Tainted: [B]=BAD_PAGE, [N]=TEST [ 36.574617] Hardware name: IBM 3931 A01 703 (KVM/Linux) [ 36.574755] ===================================================== [ 63.532541] ===================================================== [ 63.533639] BUG: KMSAN: uninit-value in virtqueue_add+0x35c6/0x7c70 [ 63.533989] virtqueue_add+0x35c6/0x7c70 [ 63.534940] virtqueue_add_outbuf+0xa0/0xb0 [ 63.535861] start_xmit+0x288c/0x4a20 [ 63.536708] dev_hard_start_xmit+0x302/0x900 [ 63.537020] sch_direct_xmit+0x340/0xea0 [ 63.537997] __dev_queue_xmit+0x2e94/0x59b0 [ 63.538819] neigh_resolve_output+0x936/0xb40 [ 63.539793] ip_finish_output2+0x1ee2/0x2200 [ 63.540784] __ip_finish_output+0x272/0x7a0 [ 63.541765] ip_finish_output+0x4e/0x5e0 [ 63.542791] ip_output+0x166/0x410 [ 63.543771] ip_push_pending_frames+0x1a2/0x470 [ 63.544753] raw_sendmsg+0x1f06/0x2180 [ 63.545033] inet_sendmsg+0xe6/0x190 [ 63.546006] __sys_sendto+0x55e/0x8e0 ---truncated---
Title s390/fpu: Fix false-positive kmsan report in fpu_vstl()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-05-11T21:52:38.615Z

Reserved: 2025-12-24T10:30:51.032Z

Link: CVE-2025-68751

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-01-05T10:15:56.050

Modified: 2026-04-15T00:35:42.020

Link: CVE-2025-68751

cve-icon Redhat

Severity : Low

Publid Date: 2026-01-05T00:00:00Z

Links: CVE-2025-68751 - Bugzilla

cve-icon OpenCVE Enrichment

No data.

Weaknesses

No weakness.