Subject: Re: [PATCH net-next 1/3] psp: add crypt-offset and spi-threshold get/set attributes

From: Willem de Bruijn <[email-masked]>
Date: Tue, 07 Apr 2026 17:37:41 -0400

Akhilesh Samineni wrote:
> crypt-offset (Crypt Offset)
> ----------------------------------
> The crypt-offset attribute specifies the byte offset within a packet
> from which encryption begins. This is a per-device attribute that
> allows a portion of the packet header to remain in plaintext while
> the rest of the payload is encrypted. This is useful in scenarios
> where intermediate nodes need to inspect or process a fixed-size
> header before the encrypted payload.
> 
> The default value is 0, meaning encryption starts from the beginning
> of the payload following the PSP header.
> 
> spi-threshold (SPI Threshold)
> ------------------------------
> The SPI (Security Parameter Index) is a 32-bit per-device identifier
> used to distinguish security associations. As SPI values are allocated
> monotonically, a threshold is needed to trigger timely SPI rotation
> before the space is exhausted.
> 
> The spi-threshold attribute allows userspace to configure the value at
> which an SPI rotation should be initiated. The default is set to
> PSP_SPI_THRESHOLD_DEFAULT (~90% of 0x7FFFFFFF), providing a comfortable
> margin to perform rotation without racing to exhaustion.
> 
> NOTE: A follow-up series will add notification support to alert
> subscribed users when the configured spi-threshold is reached, enabling
> timely SPI rotation.
> 
> Signed-off-by: Akhilesh Samineni <[email-masked]>
> Reviewed-by: Kiran Kella <[email-masked]>
> Reviewed-by: Ajit Kumar Khaparde <[email-masked]>
> ---
>  Documentation/netlink/specs/psp.yaml | 13 +++++++++++++
>  include/net/psp/types.h              |  7 +++++++
>  include/uapi/linux/psp.h             |  2 ++
>  net/psp/psp-nl-gen.c                 |  6 ++++--
>  net/psp/psp_main.c                   |  3 +++
>  net/psp/psp_nl.c                     | 27 +++++++++++++++++++++++----
>  6 files changed, 52 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/netlink/specs/psp.yaml b/Documentation/netlink/specs/psp.yaml
> index f3a57782d2cf..b22869be91cf 100644
> --- a/Documentation/netlink/specs/psp.yaml
> +++ b/Documentation/netlink/specs/psp.yaml
> @@ -38,6 +38,15 @@ attribute-sets:
>          type: u32
>          enum: version
>          enum-as-flags: true
> +      -
> +        name: crypt-offset
> +        doc: The offset from the end of the PSP header to the start of the encrypted payload.

In 4 octet units?

> +        type: u8
> +      -
> +        name: spi-threshold
> +        doc: Threshold for the SPI to trigger notification to the user for appropriate rotate action.
> +        type: u32
> +
>    -
>      name: assoc
>      attributes:
> @@ -170,6 +179,8 @@ operations:
>              - ifindex
>              - psp-versions-cap
>              - psp-versions-ena
> +            - crypt-offset
> +            - spi-threshold
>          pre: psp-device-get-locked
>          post: psp-device-unlock
>        dump:
> @@ -193,6 +204,8 @@ operations:
>            attributes:
>              - id
>              - psp-versions-ena
> +            - crypt-offset
> +            - spi-threshold
>          reply:
>            attributes: []
>          pre: psp-device-get-locked
> diff --git a/include/net/psp/types.h b/include/net/psp/types.h
> index 25a9096d4e7d..875f7822557f 100644
> --- a/include/net/psp/types.h
> +++ b/include/net/psp/types.h
> @@ -25,6 +25,9 @@ struct psphdr {
>  #define PSP_SPI_KEY_ID		GENMASK(30, 0)
>  #define PSP_SPI_KEY_PHASE	BIT(31)
>  
> +/* Default SPI threshold: ~90% of max SPI (0x7FFFFFFF) to allow rotation before exhaustion */
> +#define PSP_SPI_THRESHOLD_DEFAULT	0x73333333

Do you want to choose a more round number, in either hex or dec?

> +
>  #define PSPHDR_CRYPT_OFFSET	GENMASK(5, 0)
>  
>  #define PSPHDR_VERFL_SAMPLE	BIT(7)
> @@ -38,9 +41,13 @@ struct psphdr {
>  /**
>   * struct psp_dev_config - PSP device configuration
>   * @versions: PSP versions enabled on the device
> + * @crypt_offset: crypto offset configured on the device
> + * @spi_threshold: SPI threshold value on the device
>   */
>  struct psp_dev_config {
>  	u32 versions;
> +	u8 crypt_offset;
> +	u32 spi_threshold;
>  };
>  
>  /**
> diff --git a/include/uapi/linux/psp.h b/include/uapi/linux/psp.h
> index a3a336488dc3..bb390159dc72 100644
> --- a/include/uapi/linux/psp.h
> +++ b/include/uapi/linux/psp.h
> @@ -22,6 +22,8 @@ enum {
>  	PSP_A_DEV_IFINDEX,
>  	PSP_A_DEV_PSP_VERSIONS_CAP,
>  	PSP_A_DEV_PSP_VERSIONS_ENA,
> +	PSP_A_DEV_CRYPT_OFFSET,
> +	PSP_A_DEV_SPI_THRESHOLD,
>  
>  	__PSP_A_DEV_MAX,
>  	PSP_A_DEV_MAX = (__PSP_A_DEV_MAX - 1)
> diff --git a/net/psp/psp-nl-gen.c b/net/psp/psp-nl-gen.c
> index 22a48d0fa378..e50b8b80955c 100644
> --- a/net/psp/psp-nl-gen.c
> +++ b/net/psp/psp-nl-gen.c
> @@ -23,9 +23,11 @@ static const struct nla_policy psp_dev_get_nl_policy[PSP_A_DEV_ID + 1] = {
>  };
>  
>  /* PSP_CMD_DEV_SET - do */
> -static const struct nla_policy psp_dev_set_nl_policy[PSP_A_DEV_PSP_VERSIONS_ENA + 1] = {
> +static const struct nla_policy psp_dev_set_nl_policy[PSP_A_DEV_SPI_THRESHOLD + 1] = {
>  	[PSP_A_DEV_ID] = NLA_POLICY_MIN(NLA_U32, 1),
>  	[PSP_A_DEV_PSP_VERSIONS_ENA] = NLA_POLICY_MASK(NLA_U32, 0xf),
> +	[PSP_A_DEV_CRYPT_OFFSET] = { .type = NLA_U8, },
> +	[PSP_A_DEV_SPI_THRESHOLD] = { .type = NLA_U32, },
>  };
>  
>  /* PSP_CMD_KEY_ROTATE - do */
> @@ -75,7 +77,7 @@ static const struct genl_split_ops psp_nl_ops[] = {
>  		.doit		= psp_nl_dev_set_doit,
>  		.post_doit	= psp_device_unlock,
>  		.policy		= psp_dev_set_nl_policy,
> -		.maxattr	= PSP_A_DEV_PSP_VERSIONS_ENA,
> +		.maxattr	= PSP_A_DEV_SPI_THRESHOLD,
>  		.flags		= GENL_CMD_CAP_DO,
>  	},
>  	{
> diff --git a/net/psp/psp_main.c b/net/psp/psp_main.c
> index 9508b6c38003..536ee44db09d 100644
> --- a/net/psp/psp_main.c
> +++ b/net/psp/psp_main.c
> @@ -79,6 +79,9 @@ psp_dev_create(struct net_device *netdev,
>  	INIT_LIST_HEAD(&psd->stale_assocs);
>  	refcount_set(&psd->refcnt, 1);
>  
> +	/* ~90% of 0x7FFFFFFF; allows SPI rotation well before space is exhausted */

Repeat comment. Not needed here.

> +	psd->config.spi_threshold = PSP_SPI_THRESHOLD_DEFAULT;
> +
>  	mutex_lock(&psp_devs_lock);
>  	err = xa_alloc_cyclic(&psp_devs, &psd->id, psd, xa_limit_16b,
>  			      &last_id, GFP_KERNEL);
> diff --git a/net/psp/psp_nl.c b/net/psp/psp_nl.c
> index 6afd7707ec12..fbb77460a24b 100644
> --- a/net/psp/psp_nl.c
> +++ b/net/psp/psp_nl.c
> @@ -101,7 +101,9 @@ psp_nl_dev_fill(struct psp_dev *psd, struct sk_buff *rsp,
>  	if (nla_put_u32(rsp, PSP_A_DEV_ID, psd->id) ||
>  	    nla_put_u32(rsp, PSP_A_DEV_IFINDEX, psd->main_netdev->ifindex) ||
>  	    nla_put_u32(rsp, PSP_A_DEV_PSP_VERSIONS_CAP, psd->caps->versions) ||
> -	    nla_put_u32(rsp, PSP_A_DEV_PSP_VERSIONS_ENA, psd->config.versions))
> +	    nla_put_u32(rsp, PSP_A_DEV_PSP_VERSIONS_ENA, psd->config.versions) ||
> +	    nla_put_u8(rsp, PSP_A_DEV_CRYPT_OFFSET, psd->config.crypt_offset) ||
> +	    nla_put_u32(rsp, PSP_A_DEV_SPI_THRESHOLD, psd->config.spi_threshold))
>  		goto err_cancel_msg;
>  
>  	genlmsg_end(rsp, hdr);
> @@ -193,6 +195,13 @@ int psp_nl_dev_set_doit(struct sk_buff *skb, struct genl_info *info)
>  
>  	memcpy(&new_config, &psd->config, sizeof(new_config));
>  
> +	if (!info->attrs[PSP_A_DEV_PSP_VERSIONS_ENA] &&
> +	    !info->attrs[PSP_A_DEV_CRYPT_OFFSET] &&
> +	    !info->attrs[PSP_A_DEV_SPI_THRESHOLD]) {
> +		NL_SET_ERR_MSG(info->extack, "No settings present");
> +		return -EINVAL;
> +	}
> +
>  	if (info->attrs[PSP_A_DEV_PSP_VERSIONS_ENA]) {
>  		new_config.versions =
>  			nla_get_u32(info->attrs[PSP_A_DEV_PSP_VERSIONS_ENA]);
> @@ -200,9 +209,19 @@ int psp_nl_dev_set_doit(struct sk_buff *skb, struct genl_info *info)
>  			NL_SET_ERR_MSG(info->extack, "Requested PSP versions not supported by the device");
>  			return -EINVAL;
>  		}
> -	} else {
> -		NL_SET_ERR_MSG(info->extack, "No settings present");
> -		return -EINVAL;
> +	}
> +
> +	if (info->attrs[PSP_A_DEV_CRYPT_OFFSET])
> +		new_config.crypt_offset =
> +			nla_get_u8(info->attrs[PSP_A_DEV_CRYPT_OFFSET]);

PSP defines a 6-bit field in 4 octet units. Does this need bounds checking?

> +
> +	if (info->attrs[PSP_A_DEV_SPI_THRESHOLD]) {
> +		new_config.spi_threshold =
> +			nla_get_u32(info->attrs[PSP_A_DEV_SPI_THRESHOLD]);
> +		if (new_config.spi_threshold & PSP_SPI_KEY_PHASE) {
> +			NL_SET_ERR_MSG(info->extack, "SPI threshold must not have bit 31 set");
> +			return -EINVAL;
> +		}
>  	}
>  
>  	rsp = psp_nl_reply_new(info);
> -- 
> 2.45.4
>