linux-kernel - Re: [PATCH v9 07/14] module: Move extra signature support out of core code

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Date:   Sun, 6 Mar 2022 17:46:58 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Aaron Tomlin <atomlin@...hat.com>
CC:     "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "cl@...ux.com" <cl@...ux.com>, "mbenes@...e.cz" <mbenes@...e.cz>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "jeyu@...nel.org" <jeyu@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "void@...ifault.com" <void@...ifault.com>,
        "atomlin@...mlin.com" <atomlin@...mlin.com>,
        "allen.lkml@...il.com" <allen.lkml@...il.com>,
        "joe@...ches.com" <joe@...ches.com>,
        "msuchanek@...e.de" <msuchanek@...e.de>,
        "oleksandr@...alenko.name" <oleksandr@...alenko.name>,
        "jason.wessel@...driver.com" <jason.wessel@...driver.com>,
        "daniel.thompson@...aro.org" <daniel.thompson@...aro.org>,
        "pmladek@...e.com" <pmladek@...e.com>
Subject: Re: [PATCH v9 07/14] module: Move extra signature support out of core
 code



Le 05/03/2022 à 21:37, Aaron Tomlin a écrit :
> On Wed 2022-03-02 08:08 +0000, Christophe Leroy wrote:
>> When it was in main.c, is_module_sig_enforced() was build as soon as
>> CONFIG_MODULES was set.
>>
>> Now it is only built when CONFIG_MODULE_SIG is selected, so you have to
>> modify include/linux/modules.h and have the stub
>> is_module_sig_enforced() when CONFIG_MODULE_SIG is not selected and not
>> only when CONFIG_MODULES is not selected.
> 
> Hi Christophe,
> 
> Looking at this again, perhaps I'm missing something. If I understand
> correctly, Kconfig CONFIG_MODULE_SIG cannot be selected without
> CONFIG_MODULES; also CONFIG_MODULE_SIG depends on CONFIG_MODULES, no?
> So, what is present is enough right i.e. the stub when CONFIG_MODULES is
> not enabled?
> 

There are three possibilities:
1/ CONFIG_MODULES=n, CONFIG_MODULE_SIG=n
2/ CONFIG_MODULES=y, CONFIG_MODULE_SIG=n
3/ CONFIG_MODULES=y, CONFIG_MODULE_SIG=y

Case 1/, is_module_sig_enforced() is a static inline stub in 
linux/modules.h returning always false

Case 3/, is_module_sig_enforced() is in kernel/module/signing.c

Case 2/, is_module_sig_enforced() is nowhere.

In linux/modules.h, you have:

#ifdef CONFIG_MODULES
....
a lot of stuff
...
bool is_module_sig_enforced(void);
void set_module_sig_enforced(void);

#else
....
a lot of stuff
...
static inline bool is_module_sig_enforced(void)
{
	return false;
}

static inline void set_module_sig_enforced(void)
{
}
...
some more stuff
#endif



You must take is_module_sig_enforced() out of that #ifdef CONFIG_MODULES 
/ #else / #endif and add after the #endif /* CONFIG_MODULES */:

#ifdef CONFIG_MODULE_SIG
bool is_module_sig_enforced(void);
#else
static inline bool is_module_sig_enforced(void)
{
	return false;
}
#endif

Christophe