[PATCH 2/2] s390/fpu: Fix kmsan in fpu_vstl function

Aleksei Nikiforov
2025-11-06T16:09:30Z

clang generates call to __msan_instrument_asm_store with 1 byte as size.
Manually call kmsan helper to indicate correct amount of bytes written.

If function fpu_vstl is called with argument 'index' > 0,
it writes at least 2 bytes, but kmsan only marks first byte as written.

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
[ 63.546859] __s390x_sys_socketcall+0x19ae/0x2ba0
[ 63.547730] __do_syscall+0x12e/0x240
[ 63.548019] system_call+0x6e/0x90
[ 63.548989]
[ 63.549779] Uninit was created at:
[ 63.550691] kmem_cache_alloc_node_noprof+0x9e8/0x10e0
[ 63.550975] kmalloc_reserve+0x12a/0x470
[ 63.551969] __alloc_skb+0x310/0x860
[ 63.552949] __ip_append_data+0x483e/0x6a30
[ 63.553902] ip_append_data+0x11c/0x1e0
[ 63.554912] raw_sendmsg+0x1c8c/0x2180
[ 63.556719] inet_sendmsg+0xe6/0x190
[ 63.557534] __sys_sendto+0x55e/0x8e0
[ 63.557875] __s390x_sys_socketcall+0x19ae/0x2ba0
[ 63.558869] __do_syscall+0x12e/0x240
[ 63.559832] system_call+0x6e/0x90
[ 63.560780]
[ 63.560972] Byte 35 of 98 is uninitialized
[ 63.561741] Memory access of size 98 starts at 0000000005704312
[ 63.561950]
[ 63.562824] CPU: 3 UID: 0 PID: 192 Comm: ping Tainted: G B N 6.17.0-dirty #16 NONE
[ 63.563868] Tainted: [B]=BAD_PAGE, [N]=TEST
[ 63.564751] Hardware name: IBM 3931 A01 703 (KVM/Linux)
[ 63.564986] =====================================================

Fixes: dcd3e1de9d17 ("s390/checksum: provide csum_partial_copy_nocheck()")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Aleksei Nikiforov <aleksei.nikiforov@linux.ibm.com>
---
arch/s390/include/asm/fpu-insn.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/s390/include/asm/fpu-insn.h b/arch/s390/include/asm/fpu-insn.h
index 135bb89c0a89..151b17e22923 100644
--- a/arch/s390/include/asm/fpu-insn.h
+++ b/arch/s390/include/asm/fpu-insn.h
@@ -393,6 +393,7 @@ static __always_inline void fpu_vstl(u8 v1, u32 index, const void *vxr)
: [vxr] "=Q" (*(u8 *)vxr)
: [index] "d" (index), [v1] "I" (v1)
: "memory");
+ instrument_write_after(vxr, size);
}

#else /* CONFIG_CC_HAS_ASM_AOR_FORMAT_FLAGS */
@@ -409,6 +410,7 @@ static __always_inline void fpu_vstl(u8 v1, u32 index, const void *vxr)
: [vxr] "=R" (*(u8 *)vxr)
: [index] "d" (index), [v1] "I" (v1)
: "memory", "1");
+ instrument_write_after(vxr, size);
}

#endif /* CONFIG_CC_HAS_ASM_AOR_FORMAT_FLAGS */
--
2.43.7