linux-kernel - Re: [PATCH 05/27] kexec: Disable at runtime if the kernel is locked down

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Date:   Fri, 20 Oct 2017 14:38:37 +0800
From:   joeyli <jlee@...e.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 05/27] kexec: Disable at runtime if the kernel is locked
 down

On Thu, Oct 19, 2017 at 03:51:09PM +0100, David Howells wrote:
> From: Matthew Garrett <matthew.garrett@...ula.com>
> 
> kexec permits the loading and execution of arbitrary code in ring 0, which
> is something that lock-down is meant to prevent. It makes sense to disable
> kexec in this situation.
> 
> This does not affect kexec_file_load() which can check for a signature on the
> image to be booted.
> 
> Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> Acked-by: Dave Young <dyoung@...hat.com>

I have reviewed and tested this patch. Please feel free to add:

Reviewed-by: "Lee, Chun-Yi" <jlee@...e.com>

Thanks a lot!
Joey Lee

> cc: kexec@...ts.infradead.org
> ---
> 
>  kernel/kexec.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index e62ec4dc6620..7dadfed9b676 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -202,6 +202,13 @@ 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 (kernel_is_locked_down("kexec of unsigned images"))
> +		return -EPERM;
> +
> +	/*
>  	 * Verify we have a legal set of flags
>  	 * This leaves us room for future extensions.
>  	 */
> 
> --
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