CVE-2024-41065

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

powerpc/pseries: Whitelist dtl slub object for copying to userspace

Reading the dispatch trace log from /sys/kernel/debug/powerpc/dtl/cpu-* results in a BUG() when the config CONFIGHARDENEDUSERCOPY is enabled as shown below.

kernel BUG at mm/usercopy.c:102!
Oops: Exception in kernel mode, sig: 5 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
Modules linked in: xfs libcrc32c dm_service_time sd_mod t10_pi sg ibmvfc
scsi_transport_fc ibmveth pseries_wdt dm_multipath dm_mirror dm_region_hash dm_log dm_mod fuse
CPU: 27 PID: 1815 Comm: python3 Not tainted 6.10.0-rc3 #85
Hardware name: IBM,9040-MRX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1060.00 (NM1060_042) hv:phyp pSeries
NIP:  c0000000005d23d4 LR: c0000000005d23d0 CTR: 00000000006ee6f8
REGS: c000000120c078c0 TRAP: 0700   Not tainted  (6.10.0-rc3)
MSR:  8000000000029033 <SF,EE,ME,IR,DR,RI,LE>  CR: 2828220f  XER: 0000000e
CFAR: c0000000001fdc80 IRQMASK: 0
[ ... GPRs omitted ... ]
NIP [c0000000005d23d4] usercopy_abort+0x78/0xb0
LR [c0000000005d23d0] usercopy_abort+0x74/0xb0
Call Trace:
 usercopy_abort+0x74/0xb0 (unreliable)
 __check_heap_object+0xf8/0x120
 check_heap_object+0x218/0x240
 __check_object_size+0x84/0x1a4
 dtl_file_read+0x17c/0x2c4
 full_proxy_read+0x8c/0x110
 vfs_read+0xdc/0x3a0
 ksys_read+0x84/0x144
 system_call_exception+0x124/0x330
 system_call_vectored_common+0x15c/0x2ec
--- interrupt: 3000 at 0x7fff81f3ab34

Commit 6d07d1cd300f ("usercopy: Restrict non-usercopy caches to size 0") requires that only whitelisted areas in slab/slub objects can be copied to userspace when usercopy hardening is enabled using CONFIGHARDENEDUSERCOPY. Dtl contains hypervisor dispatch events which are expected to be read by privileged users. Hence mark this safe for user access. Specify useroffset=0 and usersize=DISPATCHLOGBYTES to whitelist the entire object.