Date:   Tue, 6 Jun 2017 09:07:04 +0800
From:   Wanlong Gao <gaowanlong@...wei.com>
To:     Jessica Yu <jeyu@...hat.com>
CC:     <gaowanlong@...wei.com>, Xie XiuQi <xiexiuqi@...wei.com>,
        <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <rusty@...tcorp.com.au>, <john.wanghui@...wei.com>,
        <wencongyang2@...wei.com>, <guijianfeng@...wei.com>
Subject: Re: [PATCH] modpost: abort if a module name is too long



On 2017/6/5 10:09, Jessica Yu wrote:
> +++ Wanlong Gao [02/06/17 11:04 +0800]:
>>
>>
>> On 2017/6/2 7:23, Jessica Yu wrote:
>>> +++ Wanlong Gao [31/05/17 11:48 +0800]:
>>>>
>>>>
>>>> On 2017/5/31 11:30, Jessica Yu wrote:
>>>>> +++ Wanlong Gao [31/05/17 10:23 +0800]:
>>>>>> Hi Jessica,
>>>>>>
>>>>>> On 2017/5/29 17:10, Jessica Yu wrote:
>>>>>>> +++ Xie XiuQi [20/05/17 15:46 +0800]:
>>>>>>>> From: Wanlong Gao <gaowanlong@...wei.com>
>>>>>>>>
>>>>>>>> Module name has a limited length, but currently the build system
>>>>>>>> allows the build finishing even if the module name is too long.
>>>>>>>>
>>>>>>>>  CC      /root/kprobe_example/abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz.mod.o
>>>>>>>> /root/kprobe_example/abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz.mod.c:9:2:
>>>>>>>> warning: initializer-string for array of chars is too long [enabled by default]
>>>>>>>>  .name = KBUILD_MODNAME,
>>>>>>>>  ^
>>>>>>>>
>>>>>>>> but it's merely a warning.
>>>>>>>>
>>>>>>>> This patch adds the check of the module name length in modpost and stops
>>>>>>>> the build properly.
>>>>>>>>
>>>>>>>> Signed-off-by: Wanlong Gao <gaowanlong@...wei.com>
>>>>>>>> Signed-off-by: Xie XiuQi <xiexiuqi@...wei.com>
>>>>>>>> ---
>>>>>>>> scripts/mod/modpost.c | 11 +++++++++++
>>>>>>>> 1 file changed, 11 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>>>>>>>> index 30d752a..db11c57 100644
>>>>>>>> --- a/scripts/mod/modpost.c
>>>>>>>> +++ b/scripts/mod/modpost.c
>>>>>>>> @@ -2166,6 +2166,17 @@ static int add_versions(struct buffer *b, struct module *mod)
>>>>>>>> {
>>>>>>>>     struct symbol *s, *exp;
>>>>>>>>     int err = 0;
>>>>>>>> +    const char *mod_name;
>>>>>>>> +
>>>>>>>> +    mod_name = strrchr(mod->name, '/');
>>>>>>>> +    if (mod_name == NULL)
>>>>>>>> +        mod_name = mod->name;
>>>>>>>> +    else
>>>>>>>> +        mod_name++;
>>>>>>>> +    if (strlen(mod_name) >= MODULE_NAME_LEN) {
>>>>>>>> +        merror("module name is too long [%s.ko]\n", mod->name);
>>>>>>>> +        return 1;
>>>>>>>> +    }
>>>>>>>
>>>>>>> Hi Xie,
>>>>>>>
>>>>>>> This check shouldn't be in add_versions() (which does something else entirely),
>>>>>>> it should probably be put in a separate helper function called from main. But
>>>>>>> I'm not a big fan of the extra string manipulation to do something this simple.
>>>>>>>
>>>>>>> I think this check can be vastly simplified, how about something like the
>>>>>>> following?
>>>>>>
>>>>>> This looks better, would you apply your following patch?
>>>>>>
>>>>>> Reviewed-by: Wanlong Gao <gaowanlong@...wei.com>
>>>>>> Tested-by: Wanlong Gao <gaowanlong@...wei.com>
>>>>>
>>>>> Sure, thanks for testing. I'll go ahead and format this into a proper
>>>>> patch and resend.
>>>>
>>>> Please wait, I just found that this patch makes the built module can't
>>>> be inserted by the following error:
>>>>
>>>> # insmod abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabc.ko
>>>> insmod: ERROR: could not insert module abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabc.ko: Invalid parameters
>>>>
>>>> # dmesg
>>>> abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabc: Unknown symbol __fentry__ (err -22)
>>>
>>> Hm, I am unable to reproduce this. It looks like __fentry__ is missing
>>> from your kernel, you may have a mismatch between the kernel config
>>> that you're running and the config you are using to build the module.
>>> In other words, it seems like you might have built the module with
>>> CONFIG_FTRACE but built the kernel without.
>>>
>>> Few questions -
>>>
>>> What is the output of running `grep __fentry__ /proc/kallsyms`?
>>>
>>
>> Sure it has.
>>
>>> Does your module correspond to the running kernel version?
>>
>> Sure.
>>
>>>
>>> Do you have CONFIG_FTRACE/FUNCTION_TRACER enabled in your running
>>> kernel?
>>>
>>
>> Sure.
>>
>>
>>> Is that the full dmesg output (are there any other error messages)?
>>
>> Even when I compiled the kernel with your patch, the kernel module load
>> failed at the boot time with the following error:
>>
>> [    1.656708] libcrc32c: no symbol version for __fentry__
>> [    1.656709] libcrc32c: Unknown symbol __fentry__ (err -22)
>>
>> But my above patch in add_versions() doesn't have such problem, I've no
>> idea why. Maybe your patch breaks some sections?
> 
> Hm, I am still unable to reproduce this on my system with modversions
> enabled and the -rc2 kernel. But judging by the errno (-22) it looks
> like this is failing in check_version()/resolve_symbol() for you,
> which leads me to think that this is somehow messing with the
> __versions table generated by modpost (not sure why).
> 
> Does the  ____versions[] array in the generated *.mod.c file for your
> test module look different with and without the patch? Also: what
> version of gcc and binutils are you using, and what kernel version are
> you testing on?

The *.mod.c file are same except the added __modname_test section, the gcc
,binutils and kernel are all from centos 7.2 (3.10.0-327).

Thanks,
Wanlong Gao

> 
> If you could also send me off-list the *.mod.c files generated by
> modpost with and without the patch applied, that'd also help.
> 
> Thanks,
> 
> Jessica
> 
>>>>>>> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>>>>>>> index 48397fe..bb09fc7 100644
>>>>>>> --- a/scripts/mod/modpost.c
>>>>>>> +++ b/scripts/mod/modpost.c
>>>>>>> @@ -2139,6 +2139,9 @@ static void add_header(struct buffer *b, struct module *mod)
>>>>>>>                   "#endif\n");
>>>>>>>     buf_printf(b, "\t.arch = MODULE_ARCH_INIT,\n");
>>>>>>>     buf_printf(b, "};\n");
>>>>>>> +    buf_printf(b, "\n");
>>>>>>> +    buf_printf(b, "static void __attribute__((section(\".discard\"), used)) __modname_test(void)\n");
>>>>>>> +    buf_printf(b, "{ BUILD_BUG_ON(sizeof(KBUILD_MODNAME) > MODULE_NAME_LEN); }\n");
>>>>>>> }
>>>>>>>
>>>>>>> static void add_intree_flag(struct buffer *b, int is_intree)
>>>>>>>
>>>>>>> This simply checks if KBUILD_MODNAME > MODULE_NAME_LEN and breaks the build if
>>>>>>> it does.
>>>>>>>
>>>>>>> Jessica
>>>>>>>
>>>>>>>>     for (s = mod->unres; s; s = s->next) {
>>>>>>>>         exp = find_symbol(s->name);
>>>>>>>> -- 
>>>>>>>> 1.8.3.1
>>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>>
>>> .
>>>
>>
> 
> .
> 

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