Re: [PATCH] modpost: abort if a module name is too long

[Wanlong Gao]

On 2017/6/2 11:04, Wanlong Gao wrote:
> 
> 
> 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@xxxxxxxxxx>
>>>>>>>
>>>>>>> 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@xxxxxxxxxx>
>>>>>>> Signed-off-by: Xie XiuQi <xiexiuqi@xxxxxxxxxx>
>>>>>>> ---
>>>>>>> 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@xxxxxxxxxx>
>>>>> Tested-by: Wanlong Gao <gaowanlong@xxxxxxxxxx>
>>>>
>>>> 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?


And FYI, if I removed the "used" in attribute, this problem goes away, the
compiled module can be inserted without error. expect that there is a
"_modname_test defined but not used" warning:

  CC      /root/kprobe_example_abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz/abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz.mod.o
/root/kprobe_example_abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz/abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz.mod.c:18:38: warning: ‘__modname_test’ defined but not used [-Wunused-function]
 __attribute__((section(".discard"))) __modname_test(void)


Any idea?

Thanks,
Wanlong Gao

> 
> Thanks,
> Wanlong Gao
> 
>>
>> 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
>>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>
>>>> .
>>>>
>>>
>>
>> .
>>
> 
> 
> .
>