Re: [PATCH 5/9] i.MX: HAB: add imx_hab_revoke_key support

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Jun 13, 2024 at 03:09:40PM +0200, Marco Felsch wrote:
> Add an helper to revoke an i.MX SRK key. At the moment the helper
> supprts i.MX8M devices only, but adding support for other SoCs can be
> done easily by providing the .revoke_key() hook.
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  drivers/hab/hab.c                | 45 ++++++++++++++++++++++++++++++++
>  include/hab.h                    |  6 +++++
>  include/mach/imx/ocotp-fusemap.h |  1 +
>  3 files changed, 52 insertions(+)
> 
> diff --git a/drivers/hab/hab.c b/drivers/hab/hab.c
> index 28a091841a69..e21a3c3acf81 100644
> --- a/drivers/hab/hab.c
> +++ b/drivers/hab/hab.c
> @@ -231,6 +231,27 @@ static int imx8m_hab_device_locked_down_ocotp(void)
>  	return v;
>  }
>  
> +static int imx8m_hab_revoke_key_ocotp(unsigned key_idx)
> +{
> +	int ret;
> +
> +	/* Prohibit revocation of last possible key */
> +	if (key_idx >= 4)
> +		return -EINVAL;
> +
> +	ret = imx_ocotp_srk_revoke_locked();
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Return -EINVAL in case the SRK_REVOKE write is locked */
> +	if (ret == 1)
> +		return -EINVAL;
> +
> +	ret = imx_ocotp_write_field(MX8M_OCOTP_SRK_REVOKE, BIT(key_idx));
> +
> +	return ret;
> +}
> +
>  struct imx_hab_ops {
>  	int (*write_srk_hash)(const u8 *srk, unsigned flags);
>  	int (*read_srk_hash)(u8 *srk);
> @@ -238,6 +259,7 @@ struct imx_hab_ops {
>  	int (*lockdown_device)(unsigned flags);
>  	int (*device_locked_down)(void);
>  	int (*print_status)(void);
> +	int (*revoke_key)(unsigned key_idx);
>  };
>  
>  static struct imx_hab_ops imx_hab_ops_iim = {
> @@ -265,6 +287,7 @@ static struct imx_hab_ops imx8m_hab_ops_ocotp = {
>  	.device_locked_down = imx8m_hab_device_locked_down_ocotp,
>  	.permanent_write_enable = imx_hab_permanent_write_enable_ocotp,
>  	.print_status = imx8m_hab_print_status,
> +	.revoke_key = imx8m_hab_revoke_key_ocotp,
>  };
>  
>  static int imx_ahab_write_srk_hash(const u8 *__newsrk, unsigned flags)
> @@ -536,3 +559,25 @@ static int init_imx_hab_print_status(void)
>  	return 0;
>  }
>  postmmu_initcall(init_imx_hab_print_status);
> +
> +int imx_hab_revoke_key(unsigned key_idx, unsigned flags)

Are you anticipating more flags? If not, should we better use a boolean
flag for now?

Otherwise it's not really clear which of the IMX_SRK_* flags is used by
which function.

Sascha


> +{
> +	struct imx_hab_ops *ops = imx_get_hab_ops();
> +	int ret;
> +
> +	if (!ops || !ops->revoke_key)
> +		return -ENOSYS;
> +
> +	if (flags & IMX_SRK_REVOKE_KEY_PERMANENT) {
> +		ret = ops->permanent_write_enable(1);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	ret = ops->revoke_key(key_idx);
> +
> +	if (flags & IMX_SRK_REVOKE_KEY_PERMANENT)
> +		ops->permanent_write_enable(0);
> +
> +	return ret;
> +}
> diff --git a/include/hab.h b/include/hab.h
> index 2cef3841d149..fd32bff15ef8 100644
> --- a/include/hab.h
> +++ b/include/hab.h
> @@ -42,6 +42,11 @@ static inline int habv4_get_state(void)
>   * fuses so that the key hash can not be modified.
>   */
>  #define IMX_SRK_HASH_WRITE_LOCK		BIT(2)
> +/*
> + * Revoke the SRK key permanently, without the flag only shadow registers are
> + * written.
> + */
> +#define IMX_SRK_REVOKE_KEY_PERMANENT	BIT(3)
>  
>  bool imx_hab_srk_hash_valid(const void *buf);
>  int imx_hab_write_srk_hash(const void *buf, unsigned flags);
> @@ -51,5 +56,6 @@ int imx_hab_read_srk_hash(void *buf);
>  int imx_hab_lockdown_device(unsigned flags);
>  int imx_hab_device_locked_down(void);
>  int imx_hab_print_status(void);
> +int imx_hab_revoke_key(unsigned key_idx, unsigned flags);
>  
>  #endif /* __HABV4_H */
> diff --git a/include/mach/imx/ocotp-fusemap.h b/include/mach/imx/ocotp-fusemap.h
> index c4f94e61e8f8..e6fa96b40ba9 100644
> --- a/include/mach/imx/ocotp-fusemap.h
> +++ b/include/mach/imx/ocotp-fusemap.h
> @@ -57,5 +57,6 @@
>  #define MX8M_OCOTP_SRK_LOCK		(OCOTP_WORD(0x400) | OCOTP_BIT(9) | OCOTP_WIDTH(1))
>  #define MX8M_OCOTP_SEC_CONFIG_1		(OCOTP_WORD(0x470) | OCOTP_BIT(25) | OCOTP_WIDTH(1))
>  #define MX8MQ_OCOTP_DIR_BT_DIS		(OCOTP_WORD(0x470) | OCOTP_BIT(27) | OCOTP_WIDTH(1))
> +#define MX8M_OCOTP_SRK_REVOKE		(OCOTP_WORD(0x670) | OCOTP_BIT(0) | OCOTP_WIDTH(4))
>  
>  #endif /* __MACH_IMX_OCOTP_FUSEMAP_H */
> -- 
> 2.39.2
> 
> 
> 

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