linux-kernel - Re: [PATCH security-next v3 00/29] LSM: Explict LSM ordering

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Date:   Sun, 30 Sep 2018 11:36:15 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Kees Cook <keescook@...omium.org>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <jmorris@...ei.org>,
        John Johansen <john.johansen@...onical.com>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        "Schaufler, Casey" <casey.schaufler@...el.com>,
        LSM <linux-security-module@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH security-next v3 00/29] LSM: Explict LSM ordering

On 2018/09/30 3:18, Kees Cook wrote:
>> Just wondering what is "__lsm_name_##lsm" for...
>>
>> +#define DEFINE_LSM(lsm)                                                        \
>> +       static const char __lsm_name_##lsm[] __initconst                \
>> +               __aligned(1) = #lsm;                                    \
>> +       static struct lsm_info __lsm_##lsm                              \
>> +               __used __section(.lsm_info.init)                        \
>> +               __aligned(sizeof(unsigned long))                        \
>> +               = {                                                     \
>> +                       .name = __lsm_name_##lsm,                       \
>> +
>> +#define END_LSM          }
> 
> I wasn't super happy with the END_LSM thing, but I wanted to be able
> to declare the name as __initconst, otherwise it needlessly stays in
> memory after init. That said, it's not a huge deal, and maybe
> readability trumps a tiny meory savings?

The value of .name field is a few bytes string, and is not sensitive
information. Keeping such string in non-__initdata section unlikely
increases total memory pages required for that module.

Unless we need to generate unique address of such string for some reason,
I think that this saving is pointless.