On 2020-09-28 17:07, Sai Prakash Ranjan wrote:
There was a report of NULL pointer dereference in ETF enable
path for perf CS mode with PID. It is almost 100% reproducible
when the process to monitor is something very active such as
chrome and only with ETF as the sink. Currently in a bid to
find the pid, the owner is dereferenced via task_pid_nr() call
in tmc_enable_etf_sink_perf(). With owner being NULL, we get a
NULL pointer dereference, so check the owner before dereferencing
it to prevent the system crash.
perf record -e cs_etm/@tmc_etf0/ -N -p <pid>
Unable to handle kernel NULL pointer dereference at virtual address
0000000000000548
Mem abort info:
ESR = 0x96000006
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
Data abort info:
ISV = 0, ISS = 0x00000006
CM = 0, WnR = 0
Call trace:
tmc_enable_etf_sink+0xe4/0x280
coresight_enable_path+0x168/0x1fc
etm_event_start+0x8c/0xf8
etm_event_add+0x38/0x54
event_sched_in+0x194/0x2ac
group_sched_in+0x54/0x12c
flexible_sched_in+0xd8/0x120
visit_groups_merge+0x100/0x16c
ctx_flexible_sched_in+0x50/0x74
ctx_sched_in+0xa4/0xa8
perf_event_sched_in+0x60/0x6c
perf_event_context_sched_in+0x98/0xe0
__perf_event_task_sched_in+0x5c/0xd8
finish_task_switch+0x184/0x1cc
schedule_tail+0x20/0xec
ret_from_fork+0x4/0x18
+Peter,
I could reproduce this (without my band-aid patch 100%) even on the
latest
coresight-next tip which is on 5.9-rc5 with my debian installed on
SDM845 based board.
Hi Peter, sorry to bother you. We observe that the NULL pointer is
propagated from events core code(in the call trace below), is it even
valid for the owner(task) to be NULL?
Reproduction is as simple as below:
perf record -e cs_etm/@tmc_etf0/ -N -p 1
[ 16.411231] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000468
[ 16.420080] Mem abort info:
[ 16.422903] ESR = 0x96000004
[ 16.425988] EC = 0x25: DABT (current EL), IL = 32 bits
[ 16.431345] SET = 0, FnV = 0
[ 16.434429] EA = 0, S1PTW = 0
[ 16.437602] Data abort info:
[ 16.440506] ISV = 0, ISS = 0x00000004
[ 16.444377] CM = 0, WnR = 0
[ 16.447372] user pgtable: 4k pages, 48-bit VAs, pgdp=00000001f078c000
[ 16.453858] [0000000000000468] pgd=0000000000000000,
p4d=0000000000000000
[ 16.460704] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[ 16.466323] Modules linked in:
[ 16.469409] CPU: 5 PID: 2795 Comm: systemd Not tainted
5.9.0-rc5-g1aeb4770c2f1-dirty #6
[ 16.484046] pstate: 80400085 (Nzcv daIf +PAN -UAO BTYPE=--)
[ 16.489668] pc : tmc_enable_etf_sink+0x74/0x2e8
[ 16.494237] lr : tmc_enable_etf_sink+0x50/0x2e8
[ 16.498807] sp : ffff800010c73b20
[ 16.502149] x29: ffff800010c73b20 x28: ffff0001712b0008
[ 16.507510] x27: ffff00017c76b308 x26: ffffa1e8a227dc80
[ 16.512860] x25: 0000000000000002 x24: ffff00017c766768
[ 16.518217] x23: 0000000000000080 x22: ffff000171c192e0
[ 16.523575] x21: ffff000173868000 x20: ffff000171c19280
[ 16.528934] x19: 0000000000000002 x18: ffffffffffffffff
[ 16.534293] x17: 0000000000000000 x16: 0000000000000000
[ 16.539652] x15: ffffa1e8a1ec9948 x14: ffff800090c738a7
[ 16.545011] x13: ffff800010c738b5 x12: 0000000000000028
[ 16.550369] x11: ffffa1e8a1eea000 x10: 0000000000000000
[ 16.555728] x9 : 0000000000000000 x8 : 00000aeb00000aeb
[ 16.561088] x7 : 003000000000000c x6 : 0000000000000001
[ 16.566447] x5 : 0000000000000002 x4 : 0000000000000001
[ 16.571805] x3 : 0000000000000000 x2 : 0000000000000001
[ 16.577163] x1 : 0000000000000000 x0 : 00000000ffffffff
[ 16.582523] Call trace:
[ 16.584998] tmc_enable_etf_sink+0x74/0x2e8
[ 16.589219] coresight_enable_path+0xd8/0x208
[ 16.593608] etm_event_start+0xe8/0x128
[ 16.597481] etm_event_add+0x44/0x60
[ 16.601094] event_sched_in.isra.139+0xd0/0x218
[ 16.605664] merge_sched_in+0x148/0x370
[ 16.609536] visit_groups_merge.constprop.147+0x124/0x490
[ 16.614973] ctx_sched_in+0xc4/0x168
[ 16.618575] perf_event_sched_in+0x6c/0xa8
[ 16.622706] __perf_event_task_sched_in+0x1a0/0x1b0
[ 16.627623] finish_task_switch+0x19c/0x248
[ 16.631843] schedule_tail+0x20/0x120
[ 16.635535] ret_from_fork+0x4/0x1c
[ 16.639060] Code: 54000f20 f9400301 b9406680 f9414821 (b9446839)
[ 16.645215] ---[ end trace bf238834e81d5892 ]---
[ 16.649877] Kernel panic - not syncing: Fatal exception
Thanks,
Sai
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