Re: [PATCH] usercopy: skip the check if not a real usercopy

[Jason Yan <yanaijie@huawei.com>]

On 2019/1/9 10:26, Jason Yan wrote:
> 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.

And I tried kernel v5.0-rc1，the system directly reboot and didn't print 
any thing.


[root@localhost ~]#
[root@localhost ~]# cat functiontracer.sh
ping 127.0.0.1 -i 0.01 > /dev/null &
sleep 1
echo function > /sys/kernel/debug/tracing/current_tracer
[root@localhost ~]#
[root@localhost ~]#
[root@localhost ~]# sh functiontracer.sh
[   43.972860] hrtimer: interrupt took 3515386 ns
[    0.000000] Linux version 5.0.0-rc1-514.55.6.9.x86_64 (yanaijie@138) 
(gcc version 7.3.1 20180712 (Red Hat 7.3.1-6) (GCC)) #72 SMP Wed Jan 9 
09:25:31 CST 2019
[    0.000000] Command line: console=ttyS0 IP=192.168.25.187 
root=/dev/vda rw
[    0.000000] x86/fpu: x87 FPU will use FXSAVE
[    0.000000] BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
[    0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] 
reserved
[    0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] 
reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x00000000bffddfff] usable
[    0.000000] BIOS-e820: [mem 0x00000000bffde000-0x00000000bfffffff] 
reserved
[    0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] 
reserved
[    0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] 
reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000013fffffff] usable