linux-kernel - Re: [PATCH v9 2/8] powerpc/ima: add support to initialize ima policy rules

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Message-ID: <482b2f08-f810-6ed0-4b32-0d5e64246ece@linux.microsoft.com>
Date:   Fri, 25 Oct 2019 11:03:03 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Nayna Jain <nayna@...ux.vnet.ibm.com>,
        Nayna Jain <nayna@...ux.ibm.com>, linuxppc-dev@...abs.org,
        linux-efi@...r.kernel.org, linux-integrity@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jeremy Kerr <jk@...abs.org>,
        Matthew Garret <matthew.garret@...ula.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        George Wilson <gcwilson@...ux.ibm.com>,
        Elaine Palmer <erpalmer@...ibm.com>,
        Eric Ricther <erichte@...ux.ibm.com>,
        Oliver O'Halloran <oohall@...il.com>,
        Prakhar Srivastava <prsriva02@...il.com>
Subject: Re: [PATCH v9 2/8] powerpc/ima: add support to initialize ima policy
 rules

On 10/25/2019 10:02 AM, Nayna Jain wrote:

 >> Is there any way to not use conditional compilation in
 >> the above array definition? Maybe define different functions to get
 >> "secure_rules" for when CONFIG_MODULE_SIG_FORCE is defined and when
 >> it is not defined.
 >
 > How will you decide which function to be called ?

Define the array in the C file:

const char *const secure_rules_kernel_check[] = {
    "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
    NULL
};

const char *const secure_rules_kernel_module_check[] = {
    "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
    "appraise func=MODULE_CHECK appraise_type=imasig|modsig",
    NULL
};

And, in the header file :

extern const char *const secure_rules_kernel_check;
extern const char *const secure_rules_kernel_module_check;

#ifdef CONFIG_MODULE_SIG_FORCE
const char *secure_rules() { return secure_rules_kernel_check; }
#else
const char *secure_rules() { return secure_rules_kernel_module_check;}
#endif // #ifdef CONFIG_MODULE_SIG_FORCE

If you want to avoid duplication, secure_rules_kernel_check and 
secure_rules_kernel_module_check could be defined in separate C files 
and conditionally compiled (in Makefile).


I was just trying to suggest the guidelines given in
"Section 21) Conditional Compilation" in coding-style.rst.

It says:
Whenever possible don't use preprocessor conditionals (#ifdef, #if) in 
.c files;...

Feel free to do what you think is appropriate.

thanks,
  -lakshmi