Date:   Thu, 22 Jun 2017 09:11:22 +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 2017/6/22 0:09, Jessica Yu wrote:
> +++ Jessica Yu [06/06/17 20:41 -0700]:
>> +++ Wanlong Gao [06/06/17 09:07 +0800]:
>>>
>>>
>>> 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 for the additional info. Just FYI, I'm going to be out this
>> week and part of next week due to travelling, but I'll be able to take
>> another look at this next Thurs/Fri. If we can't resolve the issue, we
>> can just work on your original patch.
> 
> Thanks for your patience, I've just moved abroad and getting to stable
> internet has been a challenge :-/
> 
> Here's my last attempt at fixing the BUILD_BUG_ON patch (I am not sure
> why it seems to be messing with the __versions table on your setup,
> perhaps it is related to .discard usage?).
> 
> Do either of the patches below work on your setup? (try one or the
> other and let me know if either of them work..)

Sorry to say that neither ;< It seems not to add section in mod.c
is more safe.


Thanks,
Wanlong Gao

> 
> Thanks!
> 
> ---
> Variant #1 - don't put __modname_check in .discard...
> ---
> 
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 48397fe..c88a5a7 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 __used __modname_check(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)
> 
> ---
> Variant #2 - put __modname_check at the very end of .mod.c
> ---
> 
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 48397fe..37cdf36 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -2263,6 +2263,13 @@ static void add_srcversion(struct buffer *b, struct module *mod)
>     }
> }
> 
> +static void add_modname_check(struct buffer *b, struct module *mod)
> +{
> +    buf_printf(b, "\n");
> +    buf_printf(b, "static void __attribute__((section(\".discard\"), used)) __modname_check(void)\n");
> +    buf_printf(b, "{ BUILD_BUG_ON(sizeof(KBUILD_MODNAME) > MODULE_NAME_LEN); }\n");
> +}
> +
> static void write_if_changed(struct buffer *b, const char *fname)
> {
>     char *tmp;
> @@ -2497,6 +2504,7 @@ int main(int argc, char **argv)
>         add_depends(&buf, mod, modules);
>         add_moddevtable(&buf, mod);
>         add_srcversion(&buf, mod);
> +        add_modname_check(&buf, mod);
> 
>         sprintf(fname, "%s.mod.c", mod->name);
>         write_if_changed(&buf, fname);
> 
> 
> .
> 

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