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

Willem de Bruijn
2026-04-07T21:37:43Z

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 <akhilesh.samineni@broadcom.com>
> Reviewed-by: Kiran Kella <kiran.kella@broadcom.com>
> Reviewed-by: Ajit Kumar Khaparde <ajit.khaparde@broadcom.com>
> ---
> 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
>