Re: [PATCH V3 08/11] kexec: Disable at runtime if the kernel enforces module loading restrictions

From: jerry.hoemann@hp.com
To: Matthew Garrett <matthew.garrett@nebula.com>
Cc: linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org,
	keescook@chromium.org, hpa@zytor.com,
	kexec <kexec@lists.infradead.org>
Subject: Re: [PATCH V3 08/11] kexec: Disable at runtime if the kernel enforces module loading restrictions
Date: Wed, 4 Sep 2013 14:09:59 -0600	[thread overview]
Message-ID: <20130904200959.GE8540@anatevka.fc.hp.com> (raw)
In-Reply-To: <1378252218-18798-9-git-send-email-matthew.garrett@nebula.com>

On Tue, Sep 03, 2013 at 07:50:15PM -0400, Matthew Garrett wrote:
> kexec permits the loading and execution of arbitrary code in ring 0, which
> is something that module signing enforcement is meant to prevent. It makes
> sense to disable kexec in this situation.
> 
> Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

Matthew,

Disabling kexec will disable kdump, correct?

Are there plans to enable kdump on a system where secure
boot is enabled?

thanks

Jerry

> ---
>  kernel/kexec.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 59f7b55..3e2b63a 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -32,6 +32,7 @@
>  #include <linux/vmalloc.h>
>  #include <linux/swap.h>
>  #include <linux/syscore_ops.h>
> +#include <linux/module.h>
>  
>  #include <asm/page.h>
>  #include <asm/uaccess.h>
> @@ -943,6 +944,13 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
>  		return -EPERM;
>  
>  	/*
> +	 * kexec can be used to circumvent module loading restrictions, so
> +	 * prevent loading in that case
> +	 */
> +	if (secure_modules())
> +		return -EPERM;
> +
> +	/*
>  	 * Verify we have a legal set of flags
>  	 * This leaves us room for future extensions.
>  	 */
> -- 
> 1.8.3.1
> 
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Jerry Hoemann            Software Engineer              Hewlett-Packard/MODL

3404 E Harmony Rd. MS 57                        phone:  (970) 898-1022
Ft. Collins, CO 80528                           FAX:    (970) 898-XXXX
                                                email:  jerry.hoemann@hp.com
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