Change allocation of ccw_io_region so that the usercopy hardening
code can figure out that everything is fine.
s390/cio: Refactor alloc of ccw_io_region

If I attach a vfio-ccw device to my guest, I get the following warning
on the host when the host kernel is CONFIG_HARDENED_USERCOPY=y

[250757.595325] Bad or missing usercopy whitelist? Kernel memory overwrite attempt detected to SLUB object 'dma-kmalloc-512' (offset 64, size 124)!
[250757.595365] WARNING: CPU: 2 PID: 10958 at mm/usercopy.c:81 usercopy_warn+0xac/0xd8
[250757.595369] Modules linked in: kvm vhost_net vhost tap xt_CHECKSUM iptable_mangle ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack libcrc32c devlink tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables sunrpc dm_multipath s390_trng crc32_vx_s390 ghash_s390 prng aes_s390 des_s390 des_generic sha512_s390 sha1_s390 eadm_sch tape_3590 tape tape_class qeth_l2 qeth ccwgroup vfio_ccw vfio_mdev zcrypt_cex4 mdev vfio_iommu_type1 zcrypt vfio sha256_s390 sha_common zfcp scsi_transport_fc qdio dasd_eckd_mod dasd_mod
[250757.595424] CPU: 2 PID: 10958 Comm: CPU 2/KVM Not tainted 4.18.0-derp #2
[250757.595426] Hardware name: IBM 3906 M05 780 (LPAR)
...snip regs...
[250757.595523] Call Trace:
[250757.595529] ([<0000000000349210>] usercopy_warn+0xa8/0xd8)
[250757.595535]  [<000000000032daaa>] __check_heap_object+0xfa/0x160
[250757.595540]  [<0000000000349396>] __check_object_size+0x156/0x1d0
[250757.595547]  [<000003ff80332d04>] vfio_ccw_mdev_write+0x74/0x148 [vfio_ccw]
[250757.595552]  [<000000000034ed12>] __vfs_write+0x3a/0x188
[250757.595556]  [<000000000034f040>] vfs_write+0xa8/0x1b8
[250757.595559]  [<000000000034f4e6>] ksys_pwrite64+0x86/0xc0
[250757.595568]  [<00000000008959a0>] system_call+0xdc/0x2b0
[250757.595570] Last Breaking-Event-Address:
[250757.595573]  [<0000000000349210>] usercopy_warn+0xa8/0xd8

While vfio_ccw_mdev_{write|read} validates that the input position/count
does not run over the ccw_io_region struct, the usercopy code that does
copy_{to|from}_user doesn't necessarily know this. It sees the variable
length and gets worried that it's affecting a normal kmalloc'd struct,
and generates the above warning.

Adjust how the ccw_io_region is alloc'd with a whitelist to remove this
warning. The boundary checking will continue to do its thing.

Signed-off-by: Eric Farman <>
Message-Id: <>
Signed-off-by: Cornelia Huck <>
1 file changed