===DF-2422 control (cdb_ptr mid-page, cdb_len=6)===
$ /root/pass2422 -c
issuing READ(10) cdb_len=6 cdb_ptr=0x800473800 (control=1)...
returned: status=0xb
rc=0   (kernel read the 10-byte rw_10 struct from mapped user memory;
       DISK path reached, no fault)

===DF-2422 trigger (cdb_ptr at page end, next page PROT_NONE)===
$ /root/pass2422
issuing READ(10) cdb_len=6 cdb_ptr=0x800473ffa (control=0)...