linux-kernel - Re: [PATCH V2 08/10] kexec: Disable at runtime if the kernel enforces module loading restrictions

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Date:	Thu, 29 Aug 2013 14:10:52 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Matthew Garrett <matthew.garrett@...ula.com>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	jwboyer@...hat.com, keescook@...omium.org,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: Re: [PATCH V2 08/10] kexec: Disable at runtime if the kernel
 enforces module loading restrictions

On Mon, Aug 19, 2013 at 01:26:09PM -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@...ula.com>
> ---
>  kernel/kexec.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 59f7b55..1a7690f 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>
> @@ -1645,6 +1646,9 @@ int kernel_kexec(void)
>  		goto Unlock;
>  	}
>  
> +	if (secure_modules())
> +		return -EPERM;
> +

Hi Matthew, 

Why do disallow this at run time. To me denying this at kexec_load() time
sounds better. Otherwise a user will think that I loaded crash kernel
successfully and when crash actually happens, we never capture the
crash dump.

Thanks
Vivek
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