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

[Bartosz Golaszewski]

On Sun, 28 Jan 2024 at 00:26, Gaurav Kashyap <quic_gaurkash@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> Tested-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
> ---
>  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.
> + */
> +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);

Please use __free(qcom_tzmem) everywhere in this series. You can take
a look at the calls I converted in the series adding this allocator.
It's really useful - especially if the buffer is surely freed within
the same scope.

Bart

[snip]