linux-kernel - Re: [RFC PATCH 6/6] ima: prevent loading firmware into a pre-allocated buffer

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Date:   Fri, 4 May 2018 00:10:18 +0000
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Jones <pjones@...hat.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Stephen Boyd <stephen.boyd@...aro.org>
Subject: Re: [RFC PATCH 6/6] ima: prevent loading firmware into a
 pre-allocated buffer

On Tue, May 01, 2018 at 09:48:23AM -0400, Mimi Zohar wrote:
> Question: can the device access the pre-allocated buffer at any time?
> 
> By allowing devices to request firmware be loaded directly into a
> pre-allocated buffer, will this allow the device access to the firmware
> before the kernel has verified the firmware signature?
> 
> Is it dependent on the type of buffer allocated (eg. DMA)?  For example,
> qcom_mdt_load() -> qcom_scm_pas_init_image() -> dma_alloc_coherent().
> 
> With an IMA policy requiring signed firmware, this patch would prevent
> loading firmware into a pre-allocated buffer.

Android folks went silent on the other thread .. Best poke them there?

  Luis
> 
> Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> Cc: Luis R. Rodriguez <mcgrof@...e.com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Serge E. Hallyn <serge@...lyn.com>
> Cc: Stephen Boyd <stephen.boyd@...aro.org>
> ---
>  security/integrity/ima/ima_main.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index eb9c273ab81d..3098131f77c4 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -454,6 +454,15 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
>  		return 0;
>  	}
>  
> +	if (read_id == READING_FIRMWARE_PREALLOC_BUFFER) {
> +		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
> +		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> +			pr_err("Prevent device from accessing firmware prior to verifying the firmware signature.\n");
> +			return -EACCES;
> +		}
> +		return 0;
> +	}
> +
>  	if (read_id == READING_FIRMWARE_FALLBACK) {
>  		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
>  		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> -- 
> 2.7.5
> 
> 

-- 
Do not panic