linux-kernel - Re: [PATCH] integrity: Do not load MOK and MOKx when secure boot be disabled

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Message-ID: <15ff5c8f3a3ffc2929baf3accd5670bb524f2f6f.camel@linux.ibm.com>
Date:   Tue, 21 Dec 2021 07:56:04 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        James Morris <jmorris@...ei.org>
Cc:     Eric Snowberg <eric.snowberg@...cle.com>,
        David Howells <dhowells@...hat.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, "Lee, Chun-Yi" <jlee@...e.com>,
        Petr Vorel <pvorel@...e.cz>
Subject: Re: [PATCH] integrity: Do not load MOK and MOKx when secure boot be
 disabled

Hi Joey,

On Sat, 2021-12-18 at 10:09 +0800, Lee, Chun-Yi wrote:
> The security of Machine Owner Key (MOK) relies on secure boot. When
> secure boot is disabled, EFI firmware will not verify binary code. Then
> arbitrary efi binary code can modify MOK when rebooting.
> 
> This patch prevents MOK/MOKx be loaded when secure boot be disabled.
> 
> Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>

Sorry for the delay in testing this patch.  I got the booster Friday
and am still suffering from fever spikes, chills, and headaches. The
kexec selftest might need to be updated as well.

thanks,

Mimi

> ---
>  security/integrity/platform_certs/load_uefi.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
> index f290f78c3f30..08b6d12f99b4 100644
> --- a/security/integrity/platform_certs/load_uefi.c
> +++ b/security/integrity/platform_certs/load_uefi.c
> @@ -6,6 +6,7 @@
>  #include <linux/err.h>
>  #include <linux/efi.h>
>  #include <linux/slab.h>
> +#include <linux/ima.h>
>  #include <keys/asymmetric-type.h>
>  #include <keys/system_keyring.h>
>  #include "../integrity.h"
> @@ -176,6 +177,10 @@ static int __init load_uefi_certs(void)
>  		kfree(dbx);
>  	}
>  
> +	/* the MOK/MOKx can not be trusted when secure boot is disabled */
> +	if (!arch_ima_get_secureboot())
> +		return 0;
> +
>  	mokx = get_cert_list(L"MokListXRT", &mok_var, &mokxsize, &status);
>  	if (!mokx) {
>  		if (status == EFI_NOT_FOUND)