From: Anjali K anjalik@linux.ibm.com
[ Upstream commit 1a14150e1656f7a332a943154fc486504db4d586 ]
Reading the dispatch trace log from /sys/kernel/debug/powerpc/dtl/cpu-* results in a BUG() when the config CONFIG_HARDENED_USERCOPY 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 CONFIG_HARDENED_USERCOPY. 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=DISPATCH_LOG_BYTES to whitelist the entire object.
Co-developed-by: Vishal Chourasia vishalc@linux.ibm.com Signed-off-by: Vishal Chourasia vishalc@linux.ibm.com Signed-off-by: Anjali K anjalik@linux.ibm.com Reviewed-by: Srikar Dronamraju srikar@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20240614173844.746818-1-anjalik@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/platforms/pseries/setup.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c index 822be2680b792..8e4a2e8aee114 100644 --- a/arch/powerpc/platforms/pseries/setup.c +++ b/arch/powerpc/platforms/pseries/setup.c @@ -312,8 +312,8 @@ static int alloc_dispatch_log_kmem_cache(void) { void (*ctor)(void *) = get_dtl_cache_ctor();
- dtl_cache = kmem_cache_create("dtl", DISPATCH_LOG_BYTES, - DISPATCH_LOG_BYTES, 0, ctor); + dtl_cache = kmem_cache_create_usercopy("dtl", DISPATCH_LOG_BYTES, + DISPATCH_LOG_BYTES, 0, 0, DISPATCH_LOG_BYTES, ctor); if (!dtl_cache) { pr_warn("Failed to create dispatch trace log buffer cache\n"); pr_warn("Stolen time statistics will be unreliable\n");