Re: [PATCH v4 6/6] x86/ima: define arch_get_ima_policy() for x86

[Mimi Zohar <zohar@linux.ibm.com>]

Hi Eric, Nayna,

On Wed, 2018-09-26 at 17:52 +0530, Nayna Jain wrote:
> From: Eric Richter <erichte@linux.vnet.ibm.com>

> This patch implements an example arch-specific IMA policy for x86 to
> enable measurement and appraisal of any kernel image loaded for kexec,
> when CONFIG_KEXEC_VERIFY_SIG is not enabled.
> 
> For systems with CONFIG_KEXEC_VERIFY_SIG enabled, only the measurement
> rule is enabled, not the IMA-appraisal rule.

The patch itself looks good, but this patch description explains
"what" the patch is doing, not "why".  Missing is the motivation for
the patch.

Mimi

> 
> Signed-off-by: Eric Richter <erichte@linux.vnet.ibm.com>
> - Removed the policy KEXEC_ORIG_KERNEL_CHECK which was defined to
>   disable the kexec_load syscall.
> - arch_get_ima_policy() uses arch_ima_get_secureboot() to get secureboot
>   state
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
> ---
>  arch/x86/kernel/ima_arch.c     | 18 ++++++++++++++++++
>  include/linux/ima.h            |  4 ++++
>  security/integrity/ima/Kconfig |  8 ++++++++
>  3 files changed, 30 insertions(+)
> 
> diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
> index bb5a88d2b271..245976e49a55 100644
> --- a/arch/x86/kernel/ima_arch.c
> +++ b/arch/x86/kernel/ima_arch.c
> @@ -15,3 +15,21 @@ bool arch_ima_get_secureboot(void)
>  	else
>  		return false;
>  }
> +
> +/* arch rules for audit and user mode */
> +static const char * const sb_arch_rules[] = {
> +#ifndef CONFIG_KEXEC_VERIFY_SIG
> +	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
> +#endif /* CONFIG_KEXEC_VERIFY_SIG */
> +	"measure func=KEXEC_KERNEL_CHECK",
> +	NULL
> +};
> +
> +#ifdef CONFIG_IMA_ARCH_POLICY
> +const char * const *arch_get_ima_policy(void)
> +{
> +	if (arch_ima_get_secureboot())
> +		return sb_arch_rules;
> +	return NULL;
> +}
> +#endif
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 350fa957f8a6..dabd3abdf671 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -39,10 +39,14 @@ static inline bool arch_ima_get_secureboot(void)
>  }
>  #endif
>  
> +#if defined(CONFIG_X86) && defined(CONFIG_IMA_ARCH_POLICY)
> +extern const char * const *arch_get_ima_policy(void);
> +#else
>  static inline const char * const *arch_get_ima_policy(void)
>  {
>  	return NULL;
>  }
> +#endif
>  
>  #else
>  static inline int ima_bprm_check(struct linux_binprm *bprm)
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 13b446328dda..97609a76aa14 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -157,6 +157,14 @@ config IMA_APPRAISE
>  	  <http://linux-ima.sourceforge.net>
>  	  If unsure, say N.
>  
> +config IMA_ARCH_POLICY
> +        bool "Enable loading an IMA architecture specific policy"
> +        depends on KEXEC_VERIFY_SIG || IMA_APPRAISE && INTEGRITY_ASYMMETRIC_KEYS
> +        default n
> +        help
> +          This option enables loading an IMA architecture specific policy
> +          based on run time secure boot flags.
> +
>  config IMA_APPRAISE_BUILD_POLICY
>  	bool "IMA build time configured policy rules"
>  	depends on IMA_APPRAISE && INTEGRITY_ASYMMETRIC_KEYS