Re: [PATCH v4 03/15] qcom_scm: scm call for create, prepare and import keys

[Om Prakash Singh <quic_omprsing@quicinc.com>]

On 1/28/2024 4:44 AM, 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.
> 
> Signed-off-by: Gaurav Kashyap <quic_gaurkash@quicinc.com>
> Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
> ---
>   drivers/firmware/qcom/qcom_scm.c       | 182 +++++++++++++++++++++++++
>   drivers/firmware/qcom/qcom_scm.h       |   3 +
>   include/linux/firmware/qcom/qcom_scm.h |   5 +
>   3 files changed, 190 insertions(+)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 4882f8a36453..20dbab765c8e 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -1285,6 +1285,188 @@ 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..
> + *
> + * Return: longterm key size on success; -errno on failure.
Why to return parameter input value? already has it. returning 0 on 
success should be the standard unless the returned key size would change.
> + */
> +int qcom_scm_generate_ice_key(u8 *lt_key, size_t lt_key_size)
> +{
> +	struct qcom_scm_desc desc = {
> +		.svc = QCOM_SCM_SVC_ES,
> +		.cmd =  QCOM_SCM_ES_GENERATE_ICE_KEY,
> +		.arginfo = QCOM_SCM_ARGS(2, QCOM_SCM_RW, QCOM_SCM_VAL),
> +		.args[1] = lt_key_size,
> +		.owner = ARM_SMCCC_OWNER_SIP,
> +	};
> +
> +	void *lt_key_buf;
> +	int ret;
> +
> +	lt_key_buf = qcom_tzmem_alloc(__scm->mempool, lt_key_size, GFP_KERNEL);
> +	if (!lt_key_buf)
> +		return -ENOMEM;
> +
> +	desc.args[0] = qcom_tzmem_to_phys(lt_key_buf);
> +
> +	ret = qcom_scm_call(__scm->dev, &desc, NULL);
> +	if (!ret)
> +		memcpy(lt_key, lt_key_buf, lt_key_size);
> +
> +	memzero_explicit(lt_key_buf, lt_key_size);
> +	qcom_tzmem_free(lt_key_buf);
> +
> +	if (!ret)
> +		return lt_key_size;
return 0 on success. lt_key_size is input value. Caller already has it.
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(qcom_scm_generate_ice_key);
> +
> +/**
> + * qcom_scm_prepare_ice_key() - Get per boot ephemeral wrapped key
> + * @lt_key: the longterm wrapped key
> + * @lt_key_size: size of the wrapped key
> + * @eph_key: ephemeral wrapped key to be returned
> + * @eph_key_size: size of the ephemeral wrapped key
> + *
> + * Qualcomm wrapped keys (longterm keys) are rewrapped with a per-boot
> + * ephemeral key for added protection. These are ephemeral in nature as
> + * they are valid only for that boot. A create key IOCTL is used to
> + * achieve this. These are the keys that are installed into the kernel
> + * to be then unwrapped and programmed into ICE.
> + *
> + * Adds support for the create key IOCTL to interface
> + * with the secure environment to rewrap the wrapped key with an
> + * ephemeral wrapping key.
> + *
> + * Return: ephemeral key size on success; -errno on failure.
> + */
> +int qcom_scm_prepare_ice_key(const u8 *lt_key, size_t lt_key_size,
> +			     u8 *eph_key, size_t eph_key_size)
> +{
> +	struct qcom_scm_desc desc = {
> +		.svc = QCOM_SCM_SVC_ES,
> +		.cmd =  QCOM_SCM_ES_PREPARE_ICE_KEY,
> +		.arginfo = QCOM_SCM_ARGS(4, QCOM_SCM_RO,
> +					 QCOM_SCM_VAL, QCOM_SCM_RW,
> +					 QCOM_SCM_VAL),
> +		.args[1] = lt_key_size,
> +		.args[3] = eph_key_size,
> +		.owner = ARM_SMCCC_OWNER_SIP,
> +	};
> +
> +	void *eph_key_buf;
> +	void *lt_key_buf;
> +	int ret;
> +
> +	lt_key_buf = qcom_tzmem_alloc(__scm->mempool, lt_key_size, GFP_KERNEL);
> +	if (!lt_key_buf)
> +		return -ENOMEM;
> +	eph_key_buf = qcom_tzmem_alloc(__scm->mempool, eph_key_size, GFP_KERNEL);
> +	if (!eph_key_buf) {
> +		ret = -ENOMEM;
> +		goto err_free_longterm;
> +	}
> +
> +	memcpy(lt_key_buf, lt_key, lt_key_size);
> +	desc.args[0] = qcom_tzmem_to_phys(lt_key_buf);
> +	desc.args[2] = qcom_tzmem_to_phys(eph_key_buf);
> +
> +	ret = qcom_scm_call(__scm->dev, &desc, NULL);
> +	if (!ret)
> +		memcpy(eph_key, eph_key_buf, eph_key_size);
> +
> +	memzero_explicit(eph_key_buf, eph_key_size);
> +	qcom_tzmem_free(eph_key_buf);
> +
> +err_free_longterm:
> +	memzero_explicit(lt_key_buf, lt_key_size);
> +	qcom_tzmem_free(lt_key_buf);
> +
> +	if (!ret)
> +		return eph_key_size;
return 0 on success. eph_key_size is input value. Caller already has it.
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(qcom_scm_prepare_ice_key);
> +
> +/**
> + * qcom_scm_import_ice_key() - Import a wrapped key for encryption
> + * @imp_key: the raw key that is imported
> + * @imp_key_size: size of the key to be imported
> + * @lt_key: the wrapped key to be returned
> + * @lt_key_size: size of the wrapped key
> + *
> + * Conceptually, this is very similar to generate, the difference being,
> + * here we want to import a raw key and return a longterm wrapped key
> + * from it. The same create key IOCTL is used to achieve this.
> + *
> + * Adds support for the create key IOCTL to interface with
> + * the secure environment to import a raw key and generate a longterm
> + * wrapped key.
> + *
> + * Return: longterm key size on success; -errno on failure.
> + */
> +int qcom_scm_import_ice_key(const u8 *imp_key, size_t imp_key_size,
> +			    u8 *lt_key, size_t lt_key_size)
> +{
> +	struct qcom_scm_desc desc = {
> +		.svc = QCOM_SCM_SVC_ES,
> +		.cmd =  QCOM_SCM_ES_IMPORT_ICE_KEY,
> +		.arginfo = QCOM_SCM_ARGS(4, QCOM_SCM_RO,
> +					 QCOM_SCM_VAL, QCOM_SCM_RW,
> +					 QCOM_SCM_VAL),
> +		.args[1] = imp_key_size,
> +		.args[3] = lt_key_size,
> +		.owner = ARM_SMCCC_OWNER_SIP,
> +	};
> +
> +	void *imp_key_buf;
> +	void *lt_key_buf;
> +	int ret;
> +
> +	imp_key_buf = qcom_tzmem_alloc(__scm->mempool, imp_key_size, GFP_KERNEL);
> +	if (!imp_key_buf)
> +		return -ENOMEM;
> +	lt_key_buf = qcom_tzmem_alloc(__scm->mempool, lt_key_size, GFP_KERNEL);
> +	if (!lt_key_buf) {
> +		ret = -ENOMEM;
> +		goto err_free_longterm;
> +	}
> +
> +	memcpy(imp_key_buf, imp_key, imp_key_size);
> +	desc.args[0] = qcom_tzmem_to_phys(imp_key_buf);
> +	desc.args[2] = qcom_tzmem_to_phys(lt_key_buf);
> +
> +	ret = qcom_scm_call(__scm->dev, &desc, NULL);
> +	if (!ret)
> +		memcpy(lt_key, lt_key_buf, lt_key_size);
> +
> +	memzero_explicit(lt_key_buf, lt_key_size);
> +	qcom_tzmem_free(lt_key_buf);
> +
> +err_free_longterm:
> +	memzero_explicit(imp_key_buf, imp_key_size);
> +	qcom_tzmem_free(imp_key_buf);
> +
> +	if (!ret)
> +		return lt_key_size;
return 0 on success. lt_key_size is input value. Caller already has it.
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(qcom_scm_import_ice_key);
> +
>   /**
>    * qcom_scm_hdcp_available() - Check if secure environment supports HDCP.
>    *
> diff --git a/drivers/firmware/qcom/qcom_scm.h b/drivers/firmware/qcom/qcom_scm.h
> index 56ff0806f5d2..c30d6383b6de 100644
> --- a/drivers/firmware/qcom/qcom_scm.h
> +++ b/drivers/firmware/qcom/qcom_scm.h
> @@ -128,6 +128,9 @@ struct qcom_tzmem_pool *qcom_scm_get_tzmem_pool(void);
>   #define QCOM_SCM_ES_INVALIDATE_ICE_KEY	0x03
>   #define QCOM_SCM_ES_CONFIG_SET_ICE_KEY	0x04
>   #define QCOM_SCM_ES_DERIVE_SW_SECRET	0x07
> +#define QCOM_SCM_ES_GENERATE_ICE_KEY	0x08
> +#define QCOM_SCM_ES_PREPARE_ICE_KEY	0x09
> +#define QCOM_SCM_ES_IMPORT_ICE_KEY	0xA
>   
>   #define QCOM_SCM_SVC_HDCP		0x11
>   #define QCOM_SCM_HDCP_INVOKE		0x01
> diff --git a/include/linux/firmware/qcom/qcom_scm.h b/include/linux/firmware/qcom/qcom_scm.h
> index 89358478ac67..a0983a40bc09 100644
> --- a/include/linux/firmware/qcom/qcom_scm.h
> +++ b/include/linux/firmware/qcom/qcom_scm.h
> @@ -105,6 +105,11 @@ int qcom_scm_ice_set_key(u32 index, const u8 *key, u32 key_size,
>   			 enum qcom_scm_ice_cipher cipher, u32 data_unit_size);
>   int qcom_scm_derive_sw_secret(const u8 *wkey, size_t wkey_size,
>   			      u8 *sw_secret, size_t sw_secret_size);
> +int qcom_scm_generate_ice_key(u8 *lt_key, size_t lt_key_size);
> +int qcom_scm_prepare_ice_key(const u8 *lt_key, size_t lt_key_size,
> +			     u8 *eph_key, size_t eph_size);
> +int qcom_scm_import_ice_key(const u8 *imp_key, size_t imp_size,
> +			    u8 *lt_key, size_t lt_key_size);
>   
>   bool qcom_scm_hdcp_available(void);
>   int qcom_scm_hdcp_req(struct qcom_scm_hdcp_req *req, u32 req_cnt, u32 *resp);