linux-kernel - Re: [PATCH] crypto: caam: blob_gen.c: warn if key is insecure

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Date:   Fri, 4 Nov 2022 10:05:50 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Nikolaus Voss <nv@...n.de>, Horia Geanta <horia.geanta@....com>,
        Pankaj Gupta <pankaj.gupta@....com>,
        Gaurav Jain <gaurav.jain@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        David Gstir <david@...ma-star.at>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: caam: blob_gen.c: warn if key is insecure

Hello Nikolaus,

On 19.10.22 14:44, Nikolaus Voss wrote:
> If CAAM is not in "trusted" or "secure" state, a fixed non-volatile key
> is used instead of the unique device key. This is the default mode of
> operation without secure boot (HAB). In this scenario, CAAM encrypted
> blobs should be used only for testing but not in a production
> environment, so issue a warning.

Thanks for your patch.

> Signed-off-by: Nikolaus Voss <nikolaus.voss@...g-streit.com>
> ---
>  drivers/crypto/caam/blob_gen.c | 8 ++++++++
>  drivers/crypto/caam/regs.h     | 3 +++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/crypto/caam/blob_gen.c b/drivers/crypto/caam/blob_gen.c
> index 6345c7269eb0..f3e741393f65 100644
> --- a/drivers/crypto/caam/blob_gen.c
> +++ b/drivers/crypto/caam/blob_gen.c
> @@ -6,6 +6,7 @@
>  
>  #define pr_fmt(fmt) "caam blob_gen: " fmt
>  
> +#include <linux/bitfield.h>
>  #include <linux/device.h>
>  #include <soc/fsl/caam-blob.h>
>  
> @@ -62,11 +63,13 @@ int caam_process_blob(struct caam_blob_priv *priv,
>  		      struct caam_blob_info *info, bool encap)

I agree with Herbert that this may not be the best place. I think
a single warning during caam_blob_gen_init() would suffice.

>  {
>  	struct caam_blob_job_result testres;
> +	const struct caam_drv_private *ctrlpriv;
>  	struct device *jrdev = &priv->jrdev;
>  	dma_addr_t dma_in, dma_out;
>  	int op = OP_PCLID_BLOB;
>  	size_t output_len;
>  	u32 *desc;
> +	u32 moo;
>  	int ret;
>  
>  	if (info->key_mod_len > CAAM_BLOB_KEYMOD_LENGTH)
> @@ -100,6 +103,11 @@ int caam_process_blob(struct caam_blob_priv *priv,
>  		goto out_unmap_in;
>  	}
>  
> +	ctrlpriv = dev_get_drvdata(jrdev->parent);
> +	moo = FIELD_GET(CSTA_MOO, ctrlpriv->ctrl->perfmon.status);
> +	if (moo != CSTA_MOO_SECURE && moo != CSTA_MOO_TRUSTED)
> +		dev_warn(jrdev, "using insecure test key!\n");

I'd make the warning a bit more verbose, e.g.

  "device not configured for trusted/secure mode: using insecure test key!"

> +
>  	/*
>  	 * A data blob is encrypted using a blob key (BK); a random number.
>  	 * The BK is used as an AES-CCM key. The initial block (B0) and the
> diff --git a/drivers/crypto/caam/regs.h b/drivers/crypto/caam/regs.h
> index 66d6dad841bb..b7de5fb5e056 100644
> --- a/drivers/crypto/caam/regs.h
> +++ b/drivers/crypto/caam/regs.h
> @@ -426,6 +426,9 @@ struct caam_perfmon {
>  	u32 rsvd2;
>  #define CSTA_PLEND		BIT(10)
>  #define CSTA_ALT_PLEND		BIT(18)
> +#define CSTA_MOO		GENMASK(9, 8)
> +#define CSTA_MOO_SECURE	1
> +#define CSTA_MOO_TRUSTED	3

I just checked the i.MX6 and LS1046 security reference manuals and both
have Trusted as 2 (10b). 3 is fail. Does you SoC differ? Either way, please
note what SoC you were testing on in the commit message.

>  	u32 status;		/* CSTA - CAAM Status */
>  	u64 rsvd3;
>  


Cheers,
Ahmad

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