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Date: Wed, 9 Jan 2019 10:26:30 +0800
From: Jason Yan <yanaijie@...wei.com>
To: Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>
CC: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
<zhaohongjiang@...wei.com>, <miaoxie@...wei.com>, Li Bin
<huawei.libin@...wei.com>, Wei Yongjun <weiyongjun1@...wei.com>
Subject: Re: [PATCH] usercopy: skip the check if not a real usercopy
Hi all,
On 2019/1/9 7:54, Kees Cook wrote:
> I would think we'd still want to be performing bounds-checking even in
> the kernel-to-kernel case. It seems like there is some other issue
> here? Why would the check stall?
>
> Can you find out from your build what your top-of-dump line this
> resolves to? (My various kernel version builds don't share the same
> function size, so this doesn't resolve for me...)
>
> $ ./scripts/faddr2line vmlinux __check_object_size+0x1f1/0x460
>
> Maybe it's getting stuck in loop doing stack frame walking? I'd expect
> that to show up in the backtrace though (since it's noinline).
It's very easy to reproduce in qemu using my config with v4.20. Please
refer to the attachment.
I did some debug and found that check_object_size() did not stuck but
check_object_size() sometimes takes more than 30 milliseconds, and
ftrace will call __probe_kernel_write() thousands of times, which makes
the whole process stuck for more than 20 seconds.
[root@...alhost ~]# cat functiontracer.sh
ping 127.0.0.1 -i 0.01 > /dev/null &
sleep 1
echo function > /sys/kernel/debug/tracing/current_tracer
[root@...alhost ~]#
[root@...alhost ~]#
[root@...alhost ~]# sh functiontracer.sh
[ 64.641771] hrtimer: interrupt took 2996981 ns
[ 91.605642] watchdog: BUG: soft lockup - CPU#4 stuck for 23s! [sh:363]
[ 91.634624] Modules linked in:
[ 91.642420] irq event stamp: 644434
[ 91.656045] hardirqs last enabled at (644433): [<ffffffff810074b3>]
trace_hardirqs_on_thunk+0x1a/0x1c
[ 91.685643] hardirqs last disabled at (644434): [<ffffffff810074cf>]
trace_hardirqs_off_thunk+0x1a/0x1c
[ 91.704044] softirqs last enabled at (31910): [<ffffffff83a00ad1>]
__do_softirq+0xad1/0xec6
[ 91.719178] softirqs last disabled at (31889): [<ffffffff8125c61e>]
irq_exit+0x36e/0x410
[ 91.735142] CPU: 4 PID: 363 Comm: sh Not tainted
4.20.0-514.55.6.9.x86_64 #73
[ 91.749510] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-2.fc27 04/01/2014
[ 91.763355] RIP: 0010:__check_object_size+0x5/0x460
[ 91.772696] Code: 94 06 01 e9 24 ff ff ff e8 58 44 b9 ff 48 c7 c5 e0
61 d5 83 48 83 05 f9 d3 94 06 01 e9 19 ff ff ff 0f 1f 40 00 cc 8b 93 5b
1e <41> 57 41 56 41 55 41 54 41 89 d5 55 53 48 89 f5 48 89 fb 48 83 ec
[ 91.803047] RSP: 0018:ffff8880ba4cf948 EFLAGS: 00000202 ORIG_RAX:
ffffffffffffff13
[ 91.815877] RAX: 0000000000000005 RBX: ffffffff8727fce0 RCX:
ffffffff817c3e05
[ 91.827660] RDX: 0000000000000001 RSI: 0000000000000001 RDI:
ffffffff8727fce0
[ 91.838595] RBP: 0000000000000001 R08: 0000000000000000 R09:
fffffbfff0e4ff9c
[ 91.851927] R10: 0000000000000001 R11: fffffbfff0e4ff9c R12:
00007ffffffff000
[ 91.863474] R13: ffff8880014d6b90 R14: ffff8880ba41e000 R15:
0000000000000001
[ 91.876266] FS: 00007fc0d1974740(0000) GS:ffff88810ed00000(0000)
knlGS:0000000000000000
[ 91.889452] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 91.898713] CR2: 0000563a08d928d0 CR3: 00000000ba45c000 CR4:
00000000000006e0
[ 91.911489] Call Trace:
[ 91.916210] __probe_kernel_write+0x195/0x390
[ 91.925149] ftrace_write+0x67/0xa0
[ 91.931678] ftrace_replace_code+0x5b3/0xa30
[ 91.941139] ? ftrace_int3_handler+0x100/0x100
[ 91.951361] ftrace_modify_all_code+0x1f6/0x2e0
[ 91.959368] ? function_stack_trace_call+0x340/0x340
[ 91.967523] arch_ftrace_update_code+0x3a/0x70
[ 91.976491] ftrace_run_update_code+0x35/0xf0
[ 91.984167] ftrace_startup_enable+0x7a/0xa0
[ 91.992115] ftrace_startup+0x405/0x6a0
[ 92.000624] register_ftrace_function+0x76/0x150
[ 92.009144] function_trace_init+0x1bb/0x250
[ 92.018110] tracing_set_tracer+0x4af/0xa10
[ 92.026486] tracing_set_trace_write+0x40e/0x660
[ 92.038413] ? tracing_set_tracer+0xa10/0xa10
[ 92.046526] ? kasan_check_read+0x1d/0x30
[ 92.053576] ? do_raw_spin_unlock+0x6c/0x300
[ 92.061467] ? _raw_spin_unlock+0x44/0x70
[ 92.070397] ? do_anonymous_page+0x6d3/0x1030
[ 92.081349] ? tracing_set_tracer+0xa10/0xa10
[ 92.088821] __vfs_write+0x11b/0x880
[ 92.095857] ? kernel_read+0x150/0x150
[ 92.104057] ? __lock_acquire+0x925/0x1770
[ 92.111109] ? __lock_acquire+0x925/0x1770
[ 92.119004] ? pmd_alloc+0x140/0x140
[ 92.125594] ? __lock_is_held+0xe3/0x1a0
[ 92.135659] ? kasan_check_read+0x1d/0x30
[ 92.143276] ? rcu_read_lock_sched_held+0x1dd/0x210
[ 92.153367] ? rcu_sync_lockdep_assert+0xf0/0x190
[ 92.170296] ? __sb_start_write+0x1b3/0x3e0
[ 92.189716] vfs_write+0x210/0x640
[ 92.197563] ksys_write+0xe6/0x210
[ 92.205248] ? __x64_sys_read+0xe0/0xe0
[ 92.212270] ? trace_hardirqs_on_thunk+0x1a/0x1c
[ 92.222093] ? do_syscall_64+0x98/0x2b0
[ 92.228907] ? do_syscall_64+0x98/0x2b0
[ 92.238538] __x64_sys_write+0x94/0xe0
[ 92.245679] do_syscall_64+0x161/0x2b0
[ 92.254452] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 92.262656] RIP: 0033:0x7fc0d1a64ed8
[ 92.269044] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00
00 f3 0f 1e fa 48 8d 05 45 78 0d 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f
05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
[ 92.298533] RSP: 002b:00007ffdc4882138 EFLAGS: 00000246 ORIG_RAX:
0000000000000001
[ 92.310119] RAX: ffffffffffffffda RBX: 0000000000000009 RCX:
00007fc0d1a64ed8
[ 92.322580] RDX: 0000000000000009 RSI: 0000558f3eb5ff90 RDI:
0000000000000001
[ 92.334280] RBP: 0000558f3eb5ff90 R08: 000000000000000a R09:
00007fc0d1b37cc0
[ 92.346608] R10: 000000000000000a R11: 0000000000000246 R12:
00007fc0d1b38780
[ 92.366134] R13: 0000000000000009 R14: 00007fc0d1b33740 R15:
0000000000000009
[yanaijie@138 linux]$ ./scripts/faddr2line vmlinux
__check_object_size+0x5/0x460
__check_object_size+0x5/0x460:
__check_object_size at mm/usercopy.c:254
[yanaijie@138 linux]$
View attachment "functiontrace.config" of type "text/plain" (177261 bytes)
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