linux-kernel - Re: [PATCH V34 09/29] kexec_file: Restrict at runtime if the kernel is locked down

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Message-ID: <201906221654.3E113D1@keescook>
Date:   Sat, 22 Jun 2019 16:54:04 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Matthew Garrett <matthewgarrett@...gle.com>
Cc:     jmorris@...ei.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Jiri Bohac <jbohac@...e.cz>,
        David Howells <dhowells@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>, kexec@...ts.infradead.org
Subject: Re: [PATCH V34 09/29] kexec_file: Restrict at runtime if the kernel
 is locked down

On Fri, Jun 21, 2019 at 05:03:38PM -0700, Matthew Garrett wrote:
> From: Jiri Bohac <jbohac@...e.cz>
> 
> When KEXEC_SIG is not enabled, kernel should not load images through
> kexec_file systemcall if the kernel is locked down.
> 
> [Modified by David Howells to fit with modifications to the previous patch
>  and to return -EPERM if the kernel is locked down for consistency with
>  other lockdowns. Modified by Matthew Garrett to remove the IMA
>  integration, which will be replaced by integrating with the IMA
>  architecture policy patches.]
> 
> Signed-off-by: Jiri Bohac <jbohac@...e.cz>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> Signed-off-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Matthew Garrett <mjg59@...gle.com>
> Reviewed-by: Jiri Bohac <jbohac@...e.cz>
> cc: kexec@...ts.infradead.org
> ---
>  kernel/kexec_file.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index eec7e5bb2a08..27adb4312b03 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -237,7 +237,10 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  			goto out;
>  		}
>  
> -		ret = 0;
> +		ret = security_locked_down(LOCKDOWN_KEXEC);
> +		if (ret)
> +			goto out;
> +
>  		break;
>  
>  		/* All other errors are fatal, including nomem, unparseable
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

-- 
Kees Cook