linux-kernel - Re: [PATCH 03/27] Enforce module signatures if the kernel is locked down

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Date:   Thu, 02 Nov 2017 15:13:51 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        linux-efi@...r.kernel.org, matthew.garrett@...ula.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        jforbes@...hat.com
Subject: Re: [PATCH 03/27] Enforce module signatures if the kernel is locked
 down

On Thu, 2017-11-02 at 17:22 +0000, David Howells wrote:

>  #ifdef CONFIG_MODULE_SIG
> -static int module_sig_check(struct load_info *info, int flags)
> +static int module_sig_check(struct load_info *info, int flags,
> +			    bool can_do_ima_check)
>  {
>  	int err = -ENOKEY;
>  	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
> @@ -2781,13 +2783,16 @@ static int module_sig_check(struct load_info *info, int flags)
>  	}
>  
>  	/* Not having a signature is only an error if we're strict. */
> -	if (err == -ENOKEY && !sig_enforce)
> +	if (err == -ENOKEY && !sig_enforce &&
> +	    (!can_do_ima_check || !is_ima_appraise_enabled()) &&
> +	    !kernel_is_locked_down("Loading of unsigned modules"))

By this point, IMA-appraisal has already verified the kernel module
signature back in kernel_read_file_from_fd(), if it was required.
 Having a key with which to verify the appended signature or requiring
an appended signature, should not be required as well.

Mimi