linux-kernel - Re: [PATCH 07/27] kexec_file: Disable at runtime if securelevel has been set

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Date:   Thu, 02 Nov 2017 17:29:55 +0000
From:   David Howells <dhowells@...hat.com>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     dhowells@...hat.com, 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 07/27] kexec_file: Disable at runtime if securelevel has been set

Hi Mimi,

I've adjusted the patch as below.

David
---
commit bf33218ad2bf04f1b92f5c32499ab906f107864c
Author: Chun-Yi Lee <joeyli.kernel@...il.com>
Date:   Wed May 24 14:56:03 2017 +0100

    kexec_file: Restrict at runtime if the kernel is locked down
    
    When KEXEC_VERIFY_SIG is not enabled, kernel should not load images through
    kexec_file systemcall if the kernel is locked down unless IMA can be used
    to validate the image.
    
    This code was showed in Matthew's patch but not in git:
    https://lkml.org/lkml/2015/3/13/778
    
    Cc: Matthew Garrett <mjg59@...f.ucam.org>
    Signed-off-by: Chun-Yi Lee <jlee@...e.com>
    Signed-off-by: David Howells <dhowells@...hat.com>
    Reviewed-by: James Morris <james.l.morris@...cle.com>
    cc: kexec@...ts.infradead.org

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 9f48f4412297..3ba28fc3fab0 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -255,6 +255,14 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
 		return -EPERM;
 
+	/* Don't permit images to be loaded into trusted kernels if we're not
+	 * going to verify the signature on them
+	 */
+	if (!IS_ENABLED(CONFIG_KEXEC_VERIFY_SIG) &&
+	    !is_ima_appraise_enabled() &&
+	    kernel_is_locked_down("kexec of unsigned images"))
+		return -EPERM;
+
 	/* Make sure we have a legal set of flags */
 	if (flags != (flags & KEXEC_FILE_FLAGS))
 		return -EINVAL;