linux-kernel - Re: [PATCH v5 03/15] qcom_scm: scm call for create, prepare and import keys

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Date: Mon, 17 Jun 2024 10:39:49 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Gaurav Kashyap <quic_gaurkash@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, linux-scsi@...r.kernel.org, 
	andersson@...nel.org, ebiggers@...gle.com, neil.armstrong@...aro.org, 
	srinivas.kandagatla@...aro.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, 
	robh+dt@...nel.org, linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org, 
	kernel@...cinc.com, linux-crypto@...r.kernel.org, devicetree@...r.kernel.org, 
	quic_omprsing@...cinc.com, quic_nguyenb@...cinc.com, bartosz.golaszewski@...aro.org, 
	konrad.dybcio@...aro.org, ulf.hansson@...aro.org, jejb@...ux.ibm.com, 
	martin.petersen@...cle.com, mani@...nel.org, davem@...emloft.net, 
	herbert@...dor.apana.org.au, psodagud@...cinc.com, quic_apurupa@...cinc.com, 
	sonalg@...cinc.com
Subject: Re: [PATCH v5 03/15] qcom_scm: scm call for create, prepare and
 import keys

On Sun, Jun 16, 2024 at 05:50:58PM GMT, Gaurav Kashyap wrote:
> Storage encryption has two IOCTLs for creating, importing
> and preparing keys for encryption. For wrapped keys, these
> IOCTLs need to interface with Qualcomm's Trustzone, which
> require these SCM calls.
> 
> generate_key: This is used to generate and return a longterm
>               wrapped key. Trustzone achieves this by generating
> 	      a key and then wrapping it using hwkm, returning
> 	      a wrapped keyblob.
> import_key:   The functionality is similar to generate, but here,
>               a raw key is imported into hwkm and a longterm wrapped
> 	      keyblob is returned.
> prepare_key:  The longterm wrapped key from import or generate
>               is made further secure by rewrapping it with a per-boot
> 	      ephemeral wrapped key before installing it to the linux
> 	      kernel for programming to ICE.
> 
> Tested-by: Neil Armstrong <neil.armstrong@...aro.org>
> Signed-off-by: Gaurav Kashyap <quic_gaurkash@...cinc.com>
> ---
>  drivers/firmware/qcom/qcom_scm.c       | 175 +++++++++++++++++++++++++
>  drivers/firmware/qcom/qcom_scm.h       |   3 +
>  include/linux/firmware/qcom/qcom_scm.h |   5 +
>  3 files changed, 183 insertions(+)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 8f23b459c525..61a1ace3c683 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -1309,6 +1309,181 @@ int qcom_scm_derive_sw_secret(const u8 *wkey, size_t wkey_size,
>  }
>  EXPORT_SYMBOL_GPL(qcom_scm_derive_sw_secret);
>  
> +/**
> + * qcom_scm_generate_ice_key() - Generate a wrapped key for encryption.
> + * @lt_key: the wrapped key returned after key generation
> + * @lt_key_size: size of the wrapped key to be returned.
> + *
> + * Qualcomm wrapped keys need to be generated in a trusted environment.
> + * A generate key IOCTL call is used to achieve this. These are longterm
> + * in nature as they need to be generated and wrapped only once per
> + * requirement.
> + *
> + * Adds support for the create key IOCTL to interface
> + * with the secure environment to generate and return a wrapped key..

This is documentation to a function, not a changelog. Also the function
helps implementing the IOCTL. Please describe the call itself and its
behaviour. Something like:

Generate a key using built-in entropy source (or using this-and-that
PRNG) inside TZ. Wrap the key using the platform-specific
(board-specific?) Key Encryption Key and return to the caller.

The same comment applies to other SCM calls added in this patch.

-- 
With best wishes
Dmitry