On 2019/07/17 6:51, Vegard Nossum wrote:
>
...
>
> Got a different one:
>
> WARNING: CPU: 0 PID: 2150 at arch/x86/kernel/traps.c:791 do_debug+0xfe/0x240
> CPU: 0 PID: 2150 Comm: init Not tainted 5.2.0+ #124
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> Ubuntu-1.8.2-1ubuntu1 04/01/2014
> RIP: 0010:do_debug+0xfe/0x240
...
Hello Vegard
I found a way to reproduce #DB WARNING by setting hardware watchpoint to
the address arch_stack_walk_user() will touch.
[Steps to Reproduce #DB WARNING]
poc.s:
```
.global _start
.text
_start:
# exit(0)
mov $60, %rax
xor %rdi, %rdi
syscall
```
build:
# gcc -g -c poc.s; ld -o poc poc.o
setup ftrace:
# echo 1 > options/userstacktrace
# echo 1 > events/preemptirq/irq_disable/enable
exec gdb:(set hardware watch point to $rbp)
[18:28:48 root@vm loops]# gdb ./poc
GNU gdb (GDB) Fedora 8.3-6.fc30
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Type "show copying" and "show warranty" for details.
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Type "show configuration" for configuration details.
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For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./poc...
(gdb) l
1 .global _start
2
3 .text
4 _start:
5 # exit(0)
6 mov $60, %rax
7 xor %rdi, %rdi
8 syscall
(gdb) b 6
Breakpoint 1 at 0x401000: file poc.s, line 6.
(gdb) start
Function "main" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
Starting program: /root/tmp/loops/poc
Breakpoint 1, _start () at poc.s:6
6 mov $60, %rax
(gdb) set $rbp = $rsp
(gdb) p $rbp
$1 = (void *) 0x7fffffffe4b0
(gdb) rwatch *0x7fffffffe4b0
Hardware read watchpoint 2: *0x7fffffffe4b0
(gdb) c
Continuing.
[Inferior 1 (process 2744) exited normally]
dmesg:
[ 564.646159][ T2744] WARNING: CPU: 0 PID: 2744 at arch/x86/kernel/traps.c:791
do_debug+0x220/0x490
[ 564.648581][ T2744] Modules linked in:
[ 564.649530][ T2744] CPU: 0 PID: 2744 Comm: poc Tainted: G W
5.2.0+ #77
[ 564.651121][ T2744] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.12.0-2.fc30 04/01/2014
[ 564.653569][ T2744] RIP: 0010:do_debug+0x220/0x490
[ 564.654847][ T2744] Code: 00 48 8b 95 60 ff ff ff 48 b8 00 00 00 00 00 fc ff
df 48 c1 ea 03 80 3c 02 00 0f 85 03 02 00 00 41 f6 87 88 00 00 00 03 75 60 <0f>
0b 4c 89 f2 49 81 e5 ff bf ff ff 48 b8 00 00 00 00 00 fc ff df
[ 564.659905][ T2744] RSP: 0000:fffffe0000014e98 EFLAGS: 00010046
[ 564.661500][ T2744] RAX: dffffc0000000000 RBX: 1fffffc0000029d8 RCX:
1ffff1100f81c2d3
[ 564.663531][ T2744] RDX: 1fffffc0000029fc RSI: 0000000000000000 RDI:
ffffffff85c19f00
[ 564.665553][ T2744] RBP: fffffe0000014f48 R08: fffffe0000014fe8 R09:
ffff88807c0e08a0
[ 564.667637][ T2744] R10: 0000000000000001 R11: 1ffff1100d1042ba R12:
ffff88807c0e0000
[ 564.669700][ T2744] R13: 0000000000004001 R14: ffff88807c0e1698 R15:
fffffe0000014f58
[ 564.671768][ T2744] FS: 0000000000000000(0000) GS:ffff888068800000(0000)
knlGS:0000000000000000
[ 564.674032][ T2744] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 564.675752][ T2744] CR2: 0000000000000001 CR3: 000000005fe08002 CR4:
0000000000160ef0
[ 564.677570][ T2744] DR0: 00007fffffffe4b0 DR1: 0000000000000000 DR2:
0000000000000000
[ 564.679686][ T2744] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
00000000000f0602
[ 564.681788][ T2744] Call Trace:
[ 564.682700][ T2744] <#DB>
[ 564.683492][ T2744] ? trace_hardirqs_off_thunk+0x1a/0x1c
[ 564.684954][ T2744] ? do_int3+0x1f0/0x1f0
[ 564.686074][ T2744] ? trace_hardirqs_off_thunk+0x1a/0x1c
[ 564.687512][ T2744] debug+0x2d/0x70
[ 564.688456][ T2744] RIP: 0010:arch_stack_walk_user+0x7d/0xf2
[ 564.689899][ T2744] Code: 00 0f 85 8d 00 00 00 49 8b 87 d8 16 00 00 48 83 e8
10 49 39 c6 77 32 41 83 87 e8 15 00 00 01 0f 1f 00 0f ae e8 31 c0 49 8b 0e <85>
c0 75 6d 49 8b 76 08 0f 1f 00 85 c0 74 1f 65 48 8b 04 25 00 ef
[ 564.694763][ T2744] RSP: 0000:ffff888061fb7c48 EFLAGS: 00000046
[ 564.696316][ T2744] RAX: 0000000000000000 RBX: ffff88807c0e0000 RCX:
0000000000000001
[ 564.698342][ T2744] RDX: 1ffff1100ba08e93 RSI: 0000000000401009 RDI:
ffff888061fb7cbc
[ 564.700323][ T2744] RBP: ffff888061fb7c80 R08: 1ffff1100ba08e93 R09:
ffff88805d04749c
[ 564.702337][ T2744] R10: ffffed100ba08e9b R11: ffff88805d0474db R12:
ffff888061fb7cb0
[ 564.704359][ T2744] R13: ffff888061fb7f58 R14: 00007fffffffe4b0 R15:
ffff88807c0e0000
[ 564.706413][ T2744] </#DB>
[ 564.707182][ T2744] ? stack_trace_save+0xc0/0xc0
[ 564.708447][ T2744] stack_trace_save_user+0x138/0x160
[ 564.709752][ T2744] ? stack_trace_save_tsk_reliable+0x210/0x210
[ 564.711235][ T2744] ? kasan_check_read+0x11/0x20
[ 564.712358][ T2744] trace_buffer_unlock_commit_regs+0x208/0x360
[ 564.713871][ T2744] trace_event_buffer_commit+0x1a0/0x790
[ 564.715278][ T2744] ? trace_event_buffer_reserve+0x163/0x240
[ 564.716742][ T2744] trace_event_raw_event_preemptirq_template+0x156/0x200
[ 564.718431][ T2744] ? perf_trace_preemptirq_template+0x490/0x490
[ 564.719761][ T2744] ? rcu_irq_enter_irqson+0x23/0x30
[ 564.721064][ T2744] ? trace_hardirqs_off+0x28/0x180
[ 564.722337][ T2744] ? trace_hardirqs_off_thunk+0x1a/0x1c
[ 564.723729][ T2744] ? debug+0x49/0x70
[ 564.724703][ T2744] ? trace_hardirqs_off_thunk+0x1a/0x1c
[ 564.726113][ T2744] ? perf_trace_preemptirq_template+0x490/0x490
[ 564.727721][ T2744] trace_hardirqs_off_caller+0x106/0x170
[ 564.729154][ T2744] ? debug+0x44/0x70
[ 564.730108][ T2744] trace_hardirqs_off_thunk+0x1a/0x1c
[ 564.731456][ T2744] debug+0x49/0x70
[ 564.732278][ T2744] RIP: 0033:0x401009
[ 564.733155][ T2744] Code: Bad RIP value.
[ 564.734019][ T2744] RSP: 002b:00007fffffffe4b0 EFLAGS: 00000302
[ 564.735366][ T2744] RAX: 000000000000003c RBX: 0000000000000000 RCX:
0000000000000000
[ 564.737290][ T2744] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
0000000000000000
[ 564.739314][ T2744] RBP: 00007fffffffe4b0 R08: 0000000000000000 R09:
0000000000000000
[ 564.741338][ T2744] R10: 0000000000000000 R11: 0000000000000000 R12:
0000000000000000
[ 564.743311][ T2744] R13: 0000000000000000 R14: 0000000000000000 R15:
0000000000000000
[ 564.745463][ T2744] irq event stamp: 3340
[ 564.746554][ T2744] hardirqs last enabled at (3339): [<ffffffff82a04c12>]
trace_hardirqs_on_thunk+0x1a/0x1c
[ 564.748558][ T2744] hardirqs last disabled at (3340): [<ffffffff82d28b32>]
rcu_irq_enter_irqson+0x12/0x30
[ 564.750479][ T2744] softirqs last enabled at (3330): [<ffffffff85a00634>]
__do_softirq+0x634/0x9f1
[ 564.752737][ T2744] softirqs last disabled at (3319): [<ffffffff82b77920>]
irq_exit+0x150/0x180
[ 564.754933][ T2744] ---[ end trace 67c6e66ff6ba5cd0 ]---
