linux-kernel - Re: [PATCH v4 2/6] ima: prevent kexec_load syscall based on runtime secureboot flag

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Date:   Thu, 27 Sep 2018 07:33:35 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Nayna Jain <nayna@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        jforbes@...hat.com, Seth Forshee <seth.forshee@...onical.com>,
        kexec <kexec@...ts.infradead.org>
Subject: Re: [PATCH v4 2/6] ima: prevent kexec_load syscall based on runtime
 secureboot flag

[Cc'ing the kexec mailing list, and Seth]

On Wed, 2018-09-26 at 17:52 +0530, Nayna Jain wrote:
> When CONFIG_KEXEC_VERIFY_SIG is enabled, the kexec_file_load syscall
> requires the kexec'd kernel image to be signed. Distros are concerned
> about totally disabling the kexec_load syscall. As a compromise, the
> kexec_load syscall will only be disabled when CONFIG_KEXEC_VERIFY_SIG
> is configured and the system is booted with secureboot enabled.
> 
> This patch disables the kexec_load syscall only for systems booted with
> secureboot enabled.
> 
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>

Nice!

Mimi

> ---
>  security/integrity/ima/ima_main.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index dce0a8a217bb..bdb6e5563d05 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -505,20 +505,24 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>   */
>  int ima_load_data(enum kernel_load_data_id id)
>  {
> -	bool sig_enforce;
> +	bool ima_enforce, sig_enforce;
>  
> -	if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
> -		return 0;
> +	ima_enforce =
> +		(ima_appraise & IMA_APPRAISE_ENFORCE) == IMA_APPRAISE_ENFORCE;
>  
>  	switch (id) {
>  	case LOADING_KEXEC_IMAGE:
> -		if (ima_appraise & IMA_APPRAISE_KEXEC) {
> +#ifdef CONFIG_KEXEC_VERIFY_SIG
> +		if (arch_ima_get_secureboot())
> +			return -EACCES;
> +#endif
> +		if (ima_enforce && (ima_appraise & IMA_APPRAISE_KEXEC)) {
>  			pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}
>  		break;
>  	case LOADING_FIRMWARE:
> -		if (ima_appraise & IMA_APPRAISE_FIRMWARE) {
> +		if (ima_enforce && (ima_appraise & IMA_APPRAISE_FIRMWARE)) {
>  			pr_err("Prevent firmware sysfs fallback loading.\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}
> @@ -526,7 +530,8 @@ int ima_load_data(enum kernel_load_data_id id)
>  	case LOADING_MODULE:
>  		sig_enforce = is_module_sig_enforced();
>  
> -		if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES)) {
> +		if (ima_enforce && (!sig_enforce
> +				    && (ima_appraise & IMA_APPRAISE_MODULES))) {
>  			pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}