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

[Marco Felsch <m.felsch@pengutronix.de>]

On 24-06-14, Sascha Hauer wrote:
> 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?

I followed the actual concept of having separate flags but to answer you
question, no I don't anticipate more flags.

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

I added the documentation above the flag like the previous flags did.
But you're right in the end it is all about permanent write en-/disable
so this could be covered in just one flag.

Regards,
  Marco

> 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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