This is a revival of the previous patch set submitted by Richard Weinberger:
https://lore.kernel.org/linux-integrity/[email protected]/
After having been thoroughly reviewed by Jarkko, it would be great if this
could go into 6.10. :-)
v6 is here (please ignore the incorrect version number in the cover letter):
https://lore.kernel.org/keyrings/[email protected]/
v6 -> v7:
- Add Reviewed-by from Jarkko Sakkinen for patches #1 and #3
- Improved commit messages
- Changed log level for non-trusted/secure mode check from error to warning
v5 -> v6:
- Cleaned up coding style and commit messages to make the whole series more
coherent as suggested by Jarkko Sakkinen
- Added Acked-By from Jarkko Sakkinen to patch #4 - thanks!
- Rebased against next-20240307
v4 -> v5:
- Make Kconfig for trust source check scalable as suggested by Jarkko Sakkinen
- Add Acked-By from Herbert Xu to patch #1 - thanks!
v3 -> v4:
- Split changes on MAINTAINERS and documentation into dedicated patches
- Use more concise wording in commit messages as suggested by Jarkko Sakkinen
v2 -> v3:
- Addressed review comments from Jarkko Sakkinen
v1 -> v2:
- Revive and rebase to latest version
- Include review comments from Ahmad Fatoum
The Data Co-Processor (DCP) is an IP core built into many NXP SoCs such
as i.mx6ull.
Similar to the CAAM engine used in more powerful SoCs, DCP can AES-
encrypt/decrypt user data using a unique, never-disclosed,
device-specific key. Unlike CAAM though, it cannot directly wrap and
unwrap blobs in hardware. As DCP offers only the bare minimum feature
set and a blob mechanism needs aid from software. A blob in this case
is a piece of sensitive data (e.g. a key) that is encrypted and
authenticated using the device-specific key so that unwrapping can only
be done on the hardware where the blob was wrapped.
This patch series adds a DCP based, trusted-key backend and is similar
in spirit to the one by Ahmad Fatoum [0] that does the same for CAAM.
It is of interest for similar use cases as the CAAM patch set, but for
lower end devices, where CAAM is not available.
Because constructing and parsing the blob has to happen in software,
we needed to decide on a blob format and chose the following:
struct dcp_blob_fmt {
__u8 fmt_version;
__u8 blob_key[AES_KEYSIZE_128];
__u8 nonce[AES_KEYSIZE_128];
__le32 payload_len;
__u8 payload[];
} __packed;
The `fmt_version` is currently 1.
The encrypted key is stored in the payload area. It is AES-128-GCM
encrypted using `blob_key` and `nonce`, GCM auth tag is attached at
the end of the payload (`payload_len` does not include the size of
the auth tag).
The `blob_key` itself is encrypted in AES-128-ECB mode by DCP using
the OTP or UNIQUE device key. A new `blob_key` and `nonce` are generated
randomly, when sealing/exporting the DCP blob.
This patchset was tested with dm-crypt on an i.MX6ULL board.
[0] https://lore.kernel.org/keyrings/[email protected]/
David Gstir (6):
crypto: mxs-dcp: Add support for hardware-bound keys
KEYS: trusted: improve scalability of trust source config
KEYS: trusted: Introduce NXP DCP-backed trusted keys
MAINTAINERS: add entry for DCP-based trusted keys
docs: document DCP-backed trusted keys kernel params
docs: trusted-encrypted: add DCP as new trust source
.../admin-guide/kernel-parameters.txt | 13 +
.../security/keys/trusted-encrypted.rst | 85 +++++
MAINTAINERS | 9 +
drivers/crypto/mxs-dcp.c | 104 +++++-
include/keys/trusted_dcp.h | 11 +
include/soc/fsl/dcp.h | 20 ++
security/keys/trusted-keys/Kconfig | 18 +-
security/keys/trusted-keys/Makefile | 2 +
security/keys/trusted-keys/trusted_core.c | 6 +-
security/keys/trusted-keys/trusted_dcp.c | 313 ++++++++++++++++++
10 files changed, 567 insertions(+), 14 deletions(-)
create mode 100644 include/keys/trusted_dcp.h
create mode 100644 include/soc/fsl/dcp.h
create mode 100644 security/keys/trusted-keys/trusted_dcp.c
--
2.35.3
DCP (Data Co-Processor) is able to derive private keys for a fused
random seed, which can be referenced by handle but not accessed by
the CPU. Similarly, DCP is able to store arbitrary keys in four
dedicated key slots located in its secure memory area (internal SRAM).
These keys can be used to perform AES encryption.
Expose these derived keys and key slots through the crypto API via their
handle. The main purpose is to add DCP-backed trusted keys. Other
use cases are possible too (see similar existing paes implementations),
but these should carefully be evaluated as e.g. enabling AF_ALG will
give userspace full access to use keys. In scenarios with untrustworthy
userspace, this will enable en-/decryption oracles.
Co-developed-by: Richard Weinberger <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>
Co-developed-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Gstir <[email protected]>
Acked-by: Herbert Xu <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
---
drivers/crypto/mxs-dcp.c | 104 ++++++++++++++++++++++++++++++++++-----
include/soc/fsl/dcp.h | 20 ++++++++
2 files changed, 113 insertions(+), 11 deletions(-)
create mode 100644 include/soc/fsl/dcp.h
diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
index 2b3ebe0db3a6..057d73c370b7 100644
--- a/drivers/crypto/mxs-dcp.c
+++ b/drivers/crypto/mxs-dcp.c
@@ -15,6 +15,7 @@
#include <linux/platform_device.h>
#include <linux/stmp_device.h>
#include <linux/clk.h>
+#include <soc/fsl/dcp.h>
#include <crypto/aes.h>
#include <crypto/sha1.h>
@@ -101,6 +102,7 @@ struct dcp_async_ctx {
struct crypto_skcipher *fallback;
unsigned int key_len;
uint8_t key[AES_KEYSIZE_128];
+ bool key_referenced;
};
struct dcp_aes_req_ctx {
@@ -155,6 +157,7 @@ static struct dcp *global_sdcp;
#define MXS_DCP_CONTROL0_HASH_TERM (1 << 13)
#define MXS_DCP_CONTROL0_HASH_INIT (1 << 12)
#define MXS_DCP_CONTROL0_PAYLOAD_KEY (1 << 11)
+#define MXS_DCP_CONTROL0_OTP_KEY (1 << 10)
#define MXS_DCP_CONTROL0_CIPHER_ENCRYPT (1 << 8)
#define MXS_DCP_CONTROL0_CIPHER_INIT (1 << 9)
#define MXS_DCP_CONTROL0_ENABLE_HASH (1 << 6)
@@ -168,6 +171,8 @@ static struct dcp *global_sdcp;
#define MXS_DCP_CONTROL1_CIPHER_MODE_ECB (0 << 4)
#define MXS_DCP_CONTROL1_CIPHER_SELECT_AES128 (0 << 0)
+#define MXS_DCP_CONTROL1_KEY_SELECT_SHIFT 8
+
static int mxs_dcp_start_dma(struct dcp_async_ctx *actx)
{
int dma_err;
@@ -224,13 +229,16 @@ static int mxs_dcp_run_aes(struct dcp_async_ctx *actx,
struct dcp *sdcp = global_sdcp;
struct dcp_dma_desc *desc = &sdcp->coh->desc[actx->chan];
struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
+ bool key_referenced = actx->key_referenced;
int ret;
- key_phys = dma_map_single(sdcp->dev, sdcp->coh->aes_key,
- 2 * AES_KEYSIZE_128, DMA_TO_DEVICE);
- ret = dma_mapping_error(sdcp->dev, key_phys);
- if (ret)
- return ret;
+ if (!key_referenced) {
+ key_phys = dma_map_single(sdcp->dev, sdcp->coh->aes_key,
+ 2 * AES_KEYSIZE_128, DMA_TO_DEVICE);
+ ret = dma_mapping_error(sdcp->dev, key_phys);
+ if (ret)
+ return ret;
+ }
src_phys = dma_map_single(sdcp->dev, sdcp->coh->aes_in_buf,
DCP_BUF_SZ, DMA_TO_DEVICE);
@@ -255,8 +263,12 @@ static int mxs_dcp_run_aes(struct dcp_async_ctx *actx,
MXS_DCP_CONTROL0_INTERRUPT |
MXS_DCP_CONTROL0_ENABLE_CIPHER;
- /* Payload contains the key. */
- desc->control0 |= MXS_DCP_CONTROL0_PAYLOAD_KEY;
+ if (key_referenced)
+ /* Set OTP key bit to select the key via KEY_SELECT. */
+ desc->control0 |= MXS_DCP_CONTROL0_OTP_KEY;
+ else
+ /* Payload contains the key. */
+ desc->control0 |= MXS_DCP_CONTROL0_PAYLOAD_KEY;
if (rctx->enc)
desc->control0 |= MXS_DCP_CONTROL0_CIPHER_ENCRYPT;
@@ -270,6 +282,9 @@ static int mxs_dcp_run_aes(struct dcp_async_ctx *actx,
else
desc->control1 |= MXS_DCP_CONTROL1_CIPHER_MODE_CBC;
+ if (key_referenced)
+ desc->control1 |= sdcp->coh->aes_key[0] << MXS_DCP_CONTROL1_KEY_SELECT_SHIFT;
+
desc->next_cmd_addr = 0;
desc->source = src_phys;
desc->destination = dst_phys;
@@ -284,9 +299,9 @@ static int mxs_dcp_run_aes(struct dcp_async_ctx *actx,
err_dst:
dma_unmap_single(sdcp->dev, src_phys, DCP_BUF_SZ, DMA_TO_DEVICE);
err_src:
- dma_unmap_single(sdcp->dev, key_phys, 2 * AES_KEYSIZE_128,
- DMA_TO_DEVICE);
-
+ if (!key_referenced)
+ dma_unmap_single(sdcp->dev, key_phys, 2 * AES_KEYSIZE_128,
+ DMA_TO_DEVICE);
return ret;
}
@@ -453,7 +468,7 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
int ret;
- if (unlikely(actx->key_len != AES_KEYSIZE_128))
+ if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
return mxs_dcp_block_fallback(req, enc);
rctx->enc = enc;
@@ -500,6 +515,7 @@ static int mxs_dcp_aes_setkey(struct crypto_skcipher *tfm, const u8 *key,
* there can still be an operation in progress.
*/
actx->key_len = len;
+ actx->key_referenced = false;
if (len == AES_KEYSIZE_128) {
memcpy(actx->key, key, len);
return 0;
@@ -516,6 +532,32 @@ static int mxs_dcp_aes_setkey(struct crypto_skcipher *tfm, const u8 *key,
return crypto_skcipher_setkey(actx->fallback, key, len);
}
+static int mxs_dcp_aes_setrefkey(struct crypto_skcipher *tfm, const u8 *key,
+ unsigned int len)
+{
+ struct dcp_async_ctx *actx = crypto_skcipher_ctx(tfm);
+
+ if (len != DCP_PAES_KEYSIZE)
+ return -EINVAL;
+
+ switch (key[0]) {
+ case DCP_PAES_KEY_SLOT0:
+ case DCP_PAES_KEY_SLOT1:
+ case DCP_PAES_KEY_SLOT2:
+ case DCP_PAES_KEY_SLOT3:
+ case DCP_PAES_KEY_UNIQUE:
+ case DCP_PAES_KEY_OTP:
+ memcpy(actx->key, key, len);
+ actx->key_len = len;
+ actx->key_referenced = true;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
static int mxs_dcp_aes_fallback_init_tfm(struct crypto_skcipher *tfm)
{
const char *name = crypto_tfm_alg_name(crypto_skcipher_tfm(tfm));
@@ -539,6 +581,13 @@ static void mxs_dcp_aes_fallback_exit_tfm(struct crypto_skcipher *tfm)
crypto_free_skcipher(actx->fallback);
}
+static int mxs_dcp_paes_init_tfm(struct crypto_skcipher *tfm)
+{
+ crypto_skcipher_set_reqsize(tfm, sizeof(struct dcp_aes_req_ctx));
+
+ return 0;
+}
+
/*
* Hashing (SHA1/SHA256)
*/
@@ -889,6 +938,39 @@ static struct skcipher_alg dcp_aes_algs[] = {
.ivsize = AES_BLOCK_SIZE,
.init = mxs_dcp_aes_fallback_init_tfm,
.exit = mxs_dcp_aes_fallback_exit_tfm,
+ }, {
+ .base.cra_name = "ecb(paes)",
+ .base.cra_driver_name = "ecb-paes-dcp",
+ .base.cra_priority = 401,
+ .base.cra_alignmask = 15,
+ .base.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_INTERNAL,
+ .base.cra_blocksize = AES_BLOCK_SIZE,
+ .base.cra_ctxsize = sizeof(struct dcp_async_ctx),
+ .base.cra_module = THIS_MODULE,
+
+ .min_keysize = DCP_PAES_KEYSIZE,
+ .max_keysize = DCP_PAES_KEYSIZE,
+ .setkey = mxs_dcp_aes_setrefkey,
+ .encrypt = mxs_dcp_aes_ecb_encrypt,
+ .decrypt = mxs_dcp_aes_ecb_decrypt,
+ .init = mxs_dcp_paes_init_tfm,
+ }, {
+ .base.cra_name = "cbc(paes)",
+ .base.cra_driver_name = "cbc-paes-dcp",
+ .base.cra_priority = 401,
+ .base.cra_alignmask = 15,
+ .base.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_INTERNAL,
+ .base.cra_blocksize = AES_BLOCK_SIZE,
+ .base.cra_ctxsize = sizeof(struct dcp_async_ctx),
+ .base.cra_module = THIS_MODULE,
+
+ .min_keysize = DCP_PAES_KEYSIZE,
+ .max_keysize = DCP_PAES_KEYSIZE,
+ .setkey = mxs_dcp_aes_setrefkey,
+ .encrypt = mxs_dcp_aes_cbc_encrypt,
+ .decrypt = mxs_dcp_aes_cbc_decrypt,
+ .ivsize = AES_BLOCK_SIZE,
+ .init = mxs_dcp_paes_init_tfm,
},
};
diff --git a/include/soc/fsl/dcp.h b/include/soc/fsl/dcp.h
new file mode 100644
index 000000000000..3ec335d8ca8b
--- /dev/null
+++ b/include/soc/fsl/dcp.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 sigma star gmbh
+ *
+ * Specifies paes key slot handles for NXP's DCP (Data Co-Processor) to be used
+ * with the crypto_skcipher_setkey().
+ */
+
+#ifndef MXS_DCP_H
+#define MXS_DCP_H
+
+#define DCP_PAES_KEYSIZE 1
+#define DCP_PAES_KEY_SLOT0 0x00
+#define DCP_PAES_KEY_SLOT1 0x01
+#define DCP_PAES_KEY_SLOT2 0x02
+#define DCP_PAES_KEY_SLOT3 0x03
+#define DCP_PAES_KEY_UNIQUE 0xfe
+#define DCP_PAES_KEY_OTP 0xff
+
+#endif /* MXS_DCP_H */
--
2.35.3
DCP (Data Co-Processor) is the little brother of NXP's CAAM IP.
Beside of accelerated crypto operations, it also offers support for
hardware-bound keys. Using this feature it is possible to implement a blob
mechanism similar to what CAAM offers. Unlike on CAAM, constructing and
parsing the blob has to happen in software (i.e. the kernel).
The software-based blob format used by DCP trusted keys encrypts
the payload using AES-128-GCM with a freshly generated random key and nonce.
The random key itself is AES-128-ECB encrypted using the DCP unique
or OTP key.
The DCP trusted key blob format is:
/*
* struct dcp_blob_fmt - DCP BLOB format.
*
* @fmt_version: Format version, currently being %1
* @blob_key: Random AES 128 key which is used to encrypt @payload,
* @blob_key itself is encrypted with OTP or UNIQUE device key in
* AES-128-ECB mode by DCP.
* @nonce: Random nonce used for @payload encryption.
* @payload_len: Length of the plain text @payload.
* @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
* GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
*
* The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
* AES_BLOCK_SIZE.
*/
struct dcp_blob_fmt {
__u8 fmt_version;
__u8 blob_key[AES_KEYSIZE_128];
__u8 nonce[AES_KEYSIZE_128];
__le32 payload_len;
__u8 payload[];
} __packed;
By default the unique key is used. It is also possible to use the
OTP key. While the unique key should be unique it is not documented how
this key is derived. Therefore selection the OTP key is supported as
well via the use_otp_key module parameter.
Co-developed-by: Richard Weinberger <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>
Co-developed-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Gstir <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
---
include/keys/trusted_dcp.h | 11 +
security/keys/trusted-keys/Kconfig | 8 +
security/keys/trusted-keys/Makefile | 2 +
security/keys/trusted-keys/trusted_core.c | 6 +-
security/keys/trusted-keys/trusted_dcp.c | 313 ++++++++++++++++++++++
5 files changed, 339 insertions(+), 1 deletion(-)
create mode 100644 include/keys/trusted_dcp.h
create mode 100644 security/keys/trusted-keys/trusted_dcp.c
diff --git a/include/keys/trusted_dcp.h b/include/keys/trusted_dcp.h
new file mode 100644
index 000000000000..9aaa42075b40
--- /dev/null
+++ b/include/keys/trusted_dcp.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 sigma star gmbh
+ */
+
+#ifndef TRUSTED_DCP_H
+#define TRUSTED_DCP_H
+
+extern struct trusted_key_ops dcp_trusted_key_ops;
+
+#endif
diff --git a/security/keys/trusted-keys/Kconfig b/security/keys/trusted-keys/Kconfig
index 553dc117f385..1fb8aa001995 100644
--- a/security/keys/trusted-keys/Kconfig
+++ b/security/keys/trusted-keys/Kconfig
@@ -39,6 +39,14 @@ config TRUSTED_KEYS_CAAM
Enable use of NXP's Cryptographic Accelerator and Assurance Module
(CAAM) as trusted key backend.
+config TRUSTED_KEYS_DCP
+ bool "DCP-based trusted keys"
+ depends on CRYPTO_DEV_MXS_DCP >= TRUSTED_KEYS
+ default y
+ select HAVE_TRUSTED_KEYS
+ help
+ Enable use of NXP's DCP (Data Co-Processor) as trusted key backend.
+
if !HAVE_TRUSTED_KEYS
comment "No trust source selected!"
endif
diff --git a/security/keys/trusted-keys/Makefile b/security/keys/trusted-keys/Makefile
index 735aa0bc08ef..f0f3b27f688b 100644
--- a/security/keys/trusted-keys/Makefile
+++ b/security/keys/trusted-keys/Makefile
@@ -14,3 +14,5 @@ trusted-$(CONFIG_TRUSTED_KEYS_TPM) += tpm2key.asn1.o
trusted-$(CONFIG_TRUSTED_KEYS_TEE) += trusted_tee.o
trusted-$(CONFIG_TRUSTED_KEYS_CAAM) += trusted_caam.o
+
+trusted-$(CONFIG_TRUSTED_KEYS_DCP) += trusted_dcp.o
diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
index fee1ab2c734d..5113aeae5628 100644
--- a/security/keys/trusted-keys/trusted_core.c
+++ b/security/keys/trusted-keys/trusted_core.c
@@ -10,6 +10,7 @@
#include <keys/trusted-type.h>
#include <keys/trusted_tee.h>
#include <keys/trusted_caam.h>
+#include <keys/trusted_dcp.h>
#include <keys/trusted_tpm.h>
#include <linux/capability.h>
#include <linux/err.h>
@@ -30,7 +31,7 @@ MODULE_PARM_DESC(rng, "Select trusted key RNG");
static char *trusted_key_source;
module_param_named(source, trusted_key_source, charp, 0);
-MODULE_PARM_DESC(source, "Select trusted keys source (tpm, tee or caam)");
+MODULE_PARM_DESC(source, "Select trusted keys source (tpm, tee, caam or dcp)");
static const struct trusted_key_source trusted_key_sources[] = {
#if defined(CONFIG_TRUSTED_KEYS_TPM)
@@ -42,6 +43,9 @@ static const struct trusted_key_source trusted_key_sources[] = {
#if defined(CONFIG_TRUSTED_KEYS_CAAM)
{ "caam", &trusted_key_caam_ops },
#endif
+#if defined(CONFIG_TRUSTED_KEYS_DCP)
+ { "dcp", &dcp_trusted_key_ops },
+#endif
};
DEFINE_STATIC_CALL_NULL(trusted_key_seal, *trusted_key_sources[0].ops->seal);
diff --git a/security/keys/trusted-keys/trusted_dcp.c b/security/keys/trusted-keys/trusted_dcp.c
new file mode 100644
index 000000000000..16c44aafeab3
--- /dev/null
+++ b/security/keys/trusted-keys/trusted_dcp.c
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 sigma star gmbh
+ */
+
+#include <crypto/aead.h>
+#include <crypto/aes.h>
+#include <crypto/algapi.h>
+#include <crypto/gcm.h>
+#include <crypto/skcipher.h>
+#include <keys/trusted-type.h>
+#include <linux/key-type.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/scatterlist.h>
+#include <soc/fsl/dcp.h>
+
+#define DCP_BLOB_VERSION 1
+#define DCP_BLOB_AUTHLEN 16
+
+/**
+ * struct dcp_blob_fmt - DCP BLOB format.
+ *
+ * @fmt_version: Format version, currently being %1.
+ * @blob_key: Random AES 128 key which is used to encrypt @payload,
+ * @blob_key itself is encrypted with OTP or UNIQUE device key in
+ * AES-128-ECB mode by DCP.
+ * @nonce: Random nonce used for @payload encryption.
+ * @payload_len: Length of the plain text @payload.
+ * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
+ * GCM auth tag of size DCP_BLOB_AUTHLEN is attached at the end of it.
+ *
+ * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
+ * DCP_BLOB_AUTHLEN.
+ */
+struct dcp_blob_fmt {
+ __u8 fmt_version;
+ __u8 blob_key[AES_KEYSIZE_128];
+ __u8 nonce[AES_KEYSIZE_128];
+ __le32 payload_len;
+ __u8 payload[];
+} __packed;
+
+static bool use_otp_key;
+module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
+MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");
+
+static bool skip_zk_test;
+module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
+MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are zero'ed");
+
+static unsigned int calc_blob_len(unsigned int payload_len)
+{
+ return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
+}
+
+static int do_dcp_crypto(u8 *in, u8 *out, bool do_encrypt)
+{
+ struct skcipher_request *req = NULL;
+ struct scatterlist src_sg, dst_sg;
+ struct crypto_skcipher *tfm;
+ u8 paes_key[DCP_PAES_KEYSIZE];
+ DECLARE_CRYPTO_WAIT(wait);
+ int res = 0;
+
+ if (use_otp_key)
+ paes_key[0] = DCP_PAES_KEY_OTP;
+ else
+ paes_key[0] = DCP_PAES_KEY_UNIQUE;
+
+ tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
+ CRYPTO_ALG_INTERNAL);
+ if (IS_ERR(tfm)) {
+ res = PTR_ERR(tfm);
+ tfm = NULL;
+ goto out;
+ }
+
+ req = skcipher_request_alloc(tfm, GFP_NOFS);
+ if (!req) {
+ res = -ENOMEM;
+ goto out;
+ }
+
+ skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
+ CRYPTO_TFM_REQ_MAY_SLEEP,
+ crypto_req_done, &wait);
+ res = crypto_skcipher_setkey(tfm, paes_key, sizeof(paes_key));
+ if (res < 0)
+ goto out;
+
+ sg_init_one(&src_sg, in, AES_KEYSIZE_128);
+ sg_init_one(&dst_sg, out, AES_KEYSIZE_128);
+ skcipher_request_set_crypt(req, &src_sg, &dst_sg, AES_KEYSIZE_128,
+ NULL);
+
+ if (do_encrypt)
+ res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
+ else
+ res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
+
+out:
+ skcipher_request_free(req);
+ crypto_free_skcipher(tfm);
+
+ return res;
+}
+
+static int do_aead_crypto(u8 *in, u8 *out, size_t len, u8 *key, u8 *nonce,
+ bool do_encrypt)
+{
+ struct aead_request *aead_req = NULL;
+ struct scatterlist src_sg, dst_sg;
+ struct crypto_aead *aead;
+ int ret;
+
+ aead = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
+ if (IS_ERR(aead)) {
+ ret = PTR_ERR(aead);
+ goto out;
+ }
+
+ ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
+ if (ret < 0) {
+ pr_err("Can't set crypto auth tag len: %d\n", ret);
+ goto free_aead;
+ }
+
+ aead_req = aead_request_alloc(aead, GFP_KERNEL);
+ if (!aead_req) {
+ ret = -ENOMEM;
+ goto free_aead;
+ }
+
+ sg_init_one(&src_sg, in, len);
+ if (do_encrypt) {
+ /*
+ * If we encrypt our buffer has extra space for the auth tag.
+ */
+ sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
+ } else {
+ sg_init_one(&dst_sg, out, len);
+ }
+
+ aead_request_set_crypt(aead_req, &src_sg, &dst_sg, len, nonce);
+ aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL,
+ NULL);
+ aead_request_set_ad(aead_req, 0);
+
+ if (crypto_aead_setkey(aead, key, AES_KEYSIZE_128)) {
+ pr_err("Can't set crypto AEAD key\n");
+ ret = -EINVAL;
+ goto free_req;
+ }
+
+ if (do_encrypt)
+ ret = crypto_aead_encrypt(aead_req);
+ else
+ ret = crypto_aead_decrypt(aead_req);
+
+free_req:
+ aead_request_free(aead_req);
+free_aead:
+ crypto_free_aead(aead);
+out:
+ return ret;
+}
+
+static int decrypt_blob_key(u8 *key)
+{
+ return do_dcp_crypto(key, key, false);
+}
+
+static int encrypt_blob_key(u8 *key)
+{
+ return do_dcp_crypto(key, key, true);
+}
+
+static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
+{
+ struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
+ int blen, ret;
+
+ blen = calc_blob_len(p->key_len);
+ if (blen > MAX_BLOB_SIZE)
+ return -E2BIG;
+
+ b->fmt_version = DCP_BLOB_VERSION;
+ get_random_bytes(b->nonce, AES_KEYSIZE_128);
+ get_random_bytes(b->blob_key, AES_KEYSIZE_128);
+
+ ret = do_aead_crypto(p->key, b->payload, p->key_len, b->blob_key,
+ b->nonce, true);
+ if (ret) {
+ pr_err("Unable to encrypt blob payload: %i\n", ret);
+ return ret;
+ }
+
+ ret = encrypt_blob_key(b->blob_key);
+ if (ret) {
+ pr_err("Unable to encrypt blob key: %i\n", ret);
+ return ret;
+ }
+
+ b->payload_len = get_unaligned_le32(&p->key_len);
+ p->blob_len = blen;
+ return 0;
+}
+
+static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
+{
+ struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
+ int blen, ret;
+
+ if (b->fmt_version != DCP_BLOB_VERSION) {
+ pr_err("DCP blob has bad version: %i, expected %i\n",
+ b->fmt_version, DCP_BLOB_VERSION);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ p->key_len = le32_to_cpu(b->payload_len);
+ blen = calc_blob_len(p->key_len);
+ if (blen != p->blob_len) {
+ pr_err("DCP blob has bad length: %i != %i\n", blen,
+ p->blob_len);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ ret = decrypt_blob_key(b->blob_key);
+ if (ret) {
+ pr_err("Unable to decrypt blob key: %i\n", ret);
+ goto out;
+ }
+
+ ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
+ b->blob_key, b->nonce, false);
+ if (ret) {
+ pr_err("Unwrap of DCP payload failed: %i\n", ret);
+ goto out;
+ }
+
+ ret = 0;
+out:
+ return ret;
+}
+
+static int test_for_zero_key(void)
+{
+ /*
+ * Encrypting a plaintext of all 0x55 bytes will yield
+ * this ciphertext in case the DCP test key is used.
+ */
+ static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff,
+ 0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f};
+ void *buf = NULL;
+ int ret = 0;
+
+ if (skip_zk_test)
+ goto out;
+
+ buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
+ if (!buf) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ memset(buf, 0x55, AES_BLOCK_SIZE);
+
+ ret = do_dcp_crypto(buf, buf, true);
+ if (ret)
+ goto out;
+
+ if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
+ pr_warn("Device neither in secure nor trusted mode!\n");
+ ret = -EINVAL;
+ }
+out:
+ kfree(buf);
+ return ret;
+}
+
+static int trusted_dcp_init(void)
+{
+ int ret;
+
+ if (use_otp_key)
+ pr_info("Using DCP OTP key\n");
+
+ ret = test_for_zero_key();
+ if (ret) {
+ pr_warn("Test for zero'ed keys failed: %i\n", ret);
+
+ return -EINVAL;
+ }
+
+ return register_key_type(&key_type_trusted);
+}
+
+static void trusted_dcp_exit(void)
+{
+ unregister_key_type(&key_type_trusted);
+}
+
+struct trusted_key_ops dcp_trusted_key_ops = {
+ .exit = trusted_dcp_exit,
+ .init = trusted_dcp_init,
+ .seal = trusted_dcp_seal,
+ .unseal = trusted_dcp_unseal,
+ .migratable = 0,
+};
--
2.35.3
Document the kernel parameters trusted.dcp_use_otp_key
and trusted.dcp_skip_zk_test for DCP-backed trusted keys.
Co-developed-by: Richard Weinberger <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>
Co-developed-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Gstir <[email protected]>
---
Documentation/admin-guide/kernel-parameters.txt | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 24c02c704049..b6944e57768a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6698,6 +6698,7 @@
- "tpm"
- "tee"
- "caam"
+ - "dcp"
If not specified then it defaults to iterating through
the trust source list starting with TPM and assigns the
first trust source as a backend which is initialized
@@ -6713,6 +6714,18 @@
If not specified, "default" is used. In this case,
the RNG's choice is left to each individual trust source.
+ trusted.dcp_use_otp_key
+ This is intended to be used in combination with
+ trusted.source=dcp and will select the DCP OTP key
+ instead of the DCP UNIQUE key blob encryption.
+
+ trusted.dcp_skip_zk_test
+ This is intended to be used in combination with
+ trusted.source=dcp and will disable the check if all
+ the blob key is zero'ed. This is helpful for situations where
+ having this key zero'ed is acceptable. E.g. in testing
+ scenarios.
+
tsc= Disable clocksource stability checks for TSC.
Format: <string>
[x86] reliable: mark tsc clocksource as reliable, this
--
2.35.3
Update the documentation for trusted and encrypted KEYS with DCP as new
trust source:
- Describe security properties of DCP trust source
- Describe key usage
- Document blob format
Co-developed-by: Richard Weinberger <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>
Co-developed-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Oberhollenzer <[email protected]>
Signed-off-by: David Gstir <[email protected]>
---
.../security/keys/trusted-encrypted.rst | 85 +++++++++++++++++++
1 file changed, 85 insertions(+)
diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index e989b9802f92..81fb3540bb20 100644
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -42,6 +42,14 @@ safe.
randomly generated and fused into each SoC at manufacturing time.
Otherwise, a common fixed test key is used instead.
+ (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
+
+ Rooted to a one-time programmable key (OTP) that is generally burnt
+ in the on-chip fuses and is accessible to the DCP encryption engine only.
+ DCP provides two keys that can be used as root of trust: the OTP key
+ and the UNIQUE key. Default is to use the UNIQUE key, but selecting
+ the OTP key can be done via a module parameter (dcp_use_otp_key).
+
* Execution isolation
(1) TPM
@@ -57,6 +65,12 @@ safe.
Fixed set of operations running in isolated execution environment.
+ (4) DCP
+
+ Fixed set of cryptographic operations running in isolated execution
+ environment. Only basic blob key encryption is executed there.
+ The actual key sealing/unsealing is done on main processor/kernel space.
+
* Optional binding to platform integrity state
(1) TPM
@@ -79,6 +93,11 @@ safe.
Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
for platform integrity.
+ (4) DCP
+
+ Relies on Secure/Trusted boot process (called HAB by vendor) for
+ platform integrity.
+
* Interfaces and APIs
(1) TPM
@@ -94,6 +113,11 @@ safe.
Interface is specific to silicon vendor.
+ (4) DCP
+
+ Vendor-specific API that is implemented as part of the DCP crypto driver in
+ ``drivers/crypto/mxs-dcp.c``.
+
* Threat model
The strength and appropriateness of a particular trust source for a given
@@ -129,6 +153,13 @@ selected trust source:
CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
is probed.
+ * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
+
+ The DCP hardware device itself does not provide a dedicated RNG interface,
+ so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
+ a dedicated hardware RNG that is independent from DCP which can be enabled
+ to back the kernel RNG.
+
Users may override this by specifying ``trusted.rng=kernel`` on the kernel
command-line to override the used RNG with the kernel's random number pool.
@@ -231,6 +262,19 @@ Usage::
CAAM-specific format. The key length for new keys is always in bytes.
Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
+Trusted Keys usage: DCP
+-----------------------
+
+Usage::
+
+ keyctl add trusted name "new keylen" ring
+ keyctl add trusted name "load hex_blob" ring
+ keyctl print keyid
+
+"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
+specific to this DCP key-blob implementation. The key length for new keys is
+always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
+
Encrypted Keys usage
--------------------
@@ -426,3 +470,44 @@ string length.
privkey is the binary representation of TPM2B_PUBLIC excluding the
initial TPM2B header which can be reconstructed from the ASN.1 octed
string length.
+
+DCP Blob Format
+---------------
+
+The Data Co-Processor (DCP) provides hardware-bound AES keys using its
+AES encryption engine only. It does not provide direct key sealing/unsealing.
+To make DCP hardware encryption keys usable as trust source, we define
+our own custom format that uses a hardware-bound key to secure the sealing
+key stored in the key blob.
+
+Whenever a new trusted key using DCP is generated, we generate a random 128-bit
+blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
+encrypt the trusted key payload using AES-128-GCM.
+
+The BEK itself is encrypted using the hardware-bound key using the DCP's AES
+encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
+BEK-encrypted payload and authentication tag make up the blob format together
+with a version number, payload length and authentication tag::
+
+ /*
+ * struct dcp_blob_fmt - DCP BLOB format.
+ *
+ * @fmt_version: Format version, currently being %1
+ * @blob_key: Random AES 128 key which is used to encrypt @payload,
+ * @blob_key itself is encrypted with OTP or UNIQUE device key in
+ * AES-128-ECB mode by DCP.
+ * @nonce: Random nonce used for @payload encryption.
+ * @payload_len: Length of the plain text @payload.
+ * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
+ * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
+ *
+ * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
+ * AES_BLOCK_SIZE.
+ */
+ struct dcp_blob_fmt {
+ __u8 fmt_version;
+ __u8 blob_key[AES_KEYSIZE_128];
+ __u8 nonce[AES_KEYSIZE_128];
+ __le32 payload_len;
+ __u8 payload[];
+ } __packed;
--
2.35.3
On Wed Mar 27, 2024 at 10:24 AM EET, David Gstir wrote:
> Document the kernel parameters trusted.dcp_use_otp_key
> and trusted.dcp_skip_zk_test for DCP-backed trusted keys.
>
> Co-developed-by: Richard Weinberger <[email protected]>
> Signed-off-by: Richard Weinberger <[email protected]>
> Co-developed-by: David Oberhollenzer <[email protected]>
> Signed-off-by: David Oberhollenzer <[email protected]>
> Signed-off-by: David Gstir <[email protected]>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 24c02c704049..b6944e57768a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6698,6 +6698,7 @@
> - "tpm"
> - "tee"
> - "caam"
> + - "dcp"
> If not specified then it defaults to iterating through
> the trust source list starting with TPM and assigns the
> first trust source as a backend which is initialized
> @@ -6713,6 +6714,18 @@
> If not specified, "default" is used. In this case,
> the RNG's choice is left to each individual trust source.
>
> + trusted.dcp_use_otp_key
> + This is intended to be used in combination with
> + trusted.source=dcp and will select the DCP OTP key
> + instead of the DCP UNIQUE key blob encryption.
> +
> + trusted.dcp_skip_zk_test
> + This is intended to be used in combination with
> + trusted.source=dcp and will disable the check if all
> + the blob key is zero'ed. This is helpful for situations where
> + having this key zero'ed is acceptable. E.g. in testing
> + scenarios.
> +
> tsc= Disable clocksource stability checks for TSC.
> Format: <string>
> [x86] reliable: mark tsc clocksource as reliable, this
Nicely documented, i.e. even I can understand what is said here :-)
Reviewed-by: Jarkko Sakkinen <[email protected]>
BR, Jarkko
On Wed Mar 27, 2024 at 10:24 AM EET, David Gstir wrote:
> Update the documentation for trusted and encrypted KEYS with DCP as new
> trust source:
>
> - Describe security properties of DCP trust source
> - Describe key usage
> - Document blob format
>
> Co-developed-by: Richard Weinberger <[email protected]>
> Signed-off-by: Richard Weinberger <[email protected]>
> Co-developed-by: David Oberhollenzer <[email protected]>
> Signed-off-by: David Oberhollenzer <[email protected]>
> Signed-off-by: David Gstir <[email protected]>
> ---
> .../security/keys/trusted-encrypted.rst | 85 +++++++++++++++++++
> 1 file changed, 85 insertions(+)
>
> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> index e989b9802f92..81fb3540bb20 100644
> --- a/Documentation/security/keys/trusted-encrypted.rst
> +++ b/Documentation/security/keys/trusted-encrypted.rst
> @@ -42,6 +42,14 @@ safe.
> randomly generated and fused into each SoC at manufacturing time.
> Otherwise, a common fixed test key is used instead.
>
> + (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> +
> + Rooted to a one-time programmable key (OTP) that is generally burnt
> + in the on-chip fuses and is accessible to the DCP encryption engine only.
> + DCP provides two keys that can be used as root of trust: the OTP key
> + and the UNIQUE key. Default is to use the UNIQUE key, but selecting
> + the OTP key can be done via a module parameter (dcp_use_otp_key).
> +
> * Execution isolation
>
> (1) TPM
> @@ -57,6 +65,12 @@ safe.
>
> Fixed set of operations running in isolated execution environment.
>
> + (4) DCP
> +
> + Fixed set of cryptographic operations running in isolated execution
> + environment. Only basic blob key encryption is executed there.
> + The actual key sealing/unsealing is done on main processor/kernel space.
> +
> * Optional binding to platform integrity state
>
> (1) TPM
> @@ -79,6 +93,11 @@ safe.
> Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
> for platform integrity.
>
> + (4) DCP
> +
> + Relies on Secure/Trusted boot process (called HAB by vendor) for
> + platform integrity.
> +
> * Interfaces and APIs
>
> (1) TPM
> @@ -94,6 +113,11 @@ safe.
>
> Interface is specific to silicon vendor.
>
> + (4) DCP
> +
> + Vendor-specific API that is implemented as part of the DCP crypto driver in
> + ``drivers/crypto/mxs-dcp.c``.
> +
> * Threat model
>
> The strength and appropriateness of a particular trust source for a given
> @@ -129,6 +153,13 @@ selected trust source:
> CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
> is probed.
>
> + * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> +
> + The DCP hardware device itself does not provide a dedicated RNG interface,
> + so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
> + a dedicated hardware RNG that is independent from DCP which can be enabled
> + to back the kernel RNG.
> +
> Users may override this by specifying ``trusted.rng=kernel`` on the kernel
> command-line to override the used RNG with the kernel's random number pool.
>
> @@ -231,6 +262,19 @@ Usage::
> CAAM-specific format. The key length for new keys is always in bytes.
> Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
>
> +Trusted Keys usage: DCP
> +-----------------------
> +
> +Usage::
> +
> + keyctl add trusted name "new keylen" ring
> + keyctl add trusted name "load hex_blob" ring
> + keyctl print keyid
> +
> +"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
> +specific to this DCP key-blob implementation. The key length for new keys is
> +always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
> +
> Encrypted Keys usage
> --------------------
>
> @@ -426,3 +470,44 @@ string length.
> privkey is the binary representation of TPM2B_PUBLIC excluding the
> initial TPM2B header which can be reconstructed from the ASN.1 octed
> string length.
> +
> +DCP Blob Format
> +---------------
> +
> +The Data Co-Processor (DCP) provides hardware-bound AES keys using its
> +AES encryption engine only. It does not provide direct key sealing/unsealing.
> +To make DCP hardware encryption keys usable as trust source, we define
> +our own custom format that uses a hardware-bound key to secure the sealing
> +key stored in the key blob.
> +
> +Whenever a new trusted key using DCP is generated, we generate a random 128-bit
> +blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
> +encrypt the trusted key payload using AES-128-GCM.
> +
> +The BEK itself is encrypted using the hardware-bound key using the DCP's AES
> +encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
> +BEK-encrypted payload and authentication tag make up the blob format together
> +with a version number, payload length and authentication tag::
> +
> + /*
> + * struct dcp_blob_fmt - DCP BLOB format.
> + *
> + * @fmt_version: Format version, currently being %1
> + * @blob_key: Random AES 128 key which is used to encrypt @payload,
> + * @blob_key itself is encrypted with OTP or UNIQUE device key in
> + * AES-128-ECB mode by DCP.
> + * @nonce: Random nonce used for @payload encryption.
> + * @payload_len: Length of the plain text @payload.
> + * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
> + * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
> + *
> + * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
> + * AES_BLOCK_SIZE.
> + */
> + struct dcp_blob_fmt {
> + __u8 fmt_version;
> + __u8 blob_key[AES_KEYSIZE_128];
> + __u8 nonce[AES_KEYSIZE_128];
> + __le32 payload_len;
> + __u8 payload[];
> + } __packed;
I'm thinking here given that you need to replicate the same thing that
is in the source files. E.g. Documentation/gpu/i915.rst.
The rationale would so many sources so maybe it would make sense to
maintain this in the source code.
Also this documents how to generally insert documentation inline:
https://docs.kernel.org/doc-guide/kernel-doc.html
I.e. I'm feeling that this is good time to improve scalability so that
documentation will keep up to date. Also then backend specific patches
mostly go to their subdirectories and not to Documentation/ subtree
(or that would be more rare case).
So a good chance to do more than just a new backend for the benefit
of the trusted keys subsystem :-)
Also, later on if something is changed e.g. in the above struct you
don't have to do matching update to the documentation so it will save
time too (over time).
BR, Jarkko
Jarkko,
> On 27.03.2024, at 16:40, Jarkko Sakkinen <[email protected]> wrote:
>
> On Wed Mar 27, 2024 at 10:24 AM EET, David Gstir wrote:
>> Update the documentation for trusted and encrypted KEYS with DCP as new
>> trust source:
>>
>> - Describe security properties of DCP trust source
>> - Describe key usage
>> - Document blob format
>>
>> Co-developed-by: Richard Weinberger <[email protected]>
>> Signed-off-by: Richard Weinberger <[email protected]>
>> Co-developed-by: David Oberhollenzer <[email protected]>
>> Signed-off-by: David Oberhollenzer <[email protected]>
>> Signed-off-by: David Gstir <[email protected]>
>> ---
>> .../security/keys/trusted-encrypted.rst | 85 +++++++++++++++++++
>> 1 file changed, 85 insertions(+)
>>
>> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
>> index e989b9802f92..81fb3540bb20 100644
>> --- a/Documentation/security/keys/trusted-encrypted.rst
>> +++ b/Documentation/security/keys/trusted-encrypted.rst
>> @@ -42,6 +42,14 @@ safe.
>> randomly generated and fused into each SoC at manufacturing time.
>> Otherwise, a common fixed test key is used instead.
>>
>> + (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
>> +
>> + Rooted to a one-time programmable key (OTP) that is generally burnt
>> + in the on-chip fuses and is accessible to the DCP encryption engine only.
>> + DCP provides two keys that can be used as root of trust: the OTP key
>> + and the UNIQUE key. Default is to use the UNIQUE key, but selecting
>> + the OTP key can be done via a module parameter (dcp_use_otp_key).
>> +
>> * Execution isolation
>>
>> (1) TPM
>> @@ -57,6 +65,12 @@ safe.
>>
>> Fixed set of operations running in isolated execution environment.
>>
>> + (4) DCP
>> +
>> + Fixed set of cryptographic operations running in isolated execution
>> + environment. Only basic blob key encryption is executed there.
>> + The actual key sealing/unsealing is done on main processor/kernel space.
>> +
>> * Optional binding to platform integrity state
>>
>> (1) TPM
>> @@ -79,6 +93,11 @@ safe.
>> Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
>> for platform integrity.
>>
>> + (4) DCP
>> +
>> + Relies on Secure/Trusted boot process (called HAB by vendor) for
>> + platform integrity.
>> +
>> * Interfaces and APIs
>>
>> (1) TPM
>> @@ -94,6 +113,11 @@ safe.
>>
>> Interface is specific to silicon vendor.
>>
>> + (4) DCP
>> +
>> + Vendor-specific API that is implemented as part of the DCP crypto driver in
>> + ``drivers/crypto/mxs-dcp.c``.
>> +
>> * Threat model
>>
>> The strength and appropriateness of a particular trust source for a given
>> @@ -129,6 +153,13 @@ selected trust source:
>> CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
>> is probed.
>>
>> + * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
>> +
>> + The DCP hardware device itself does not provide a dedicated RNG interface,
>> + so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
>> + a dedicated hardware RNG that is independent from DCP which can be enabled
>> + to back the kernel RNG.
>> +
>> Users may override this by specifying ``trusted.rng=kernel`` on the kernel
>> command-line to override the used RNG with the kernel's random number pool.
>>
>> @@ -231,6 +262,19 @@ Usage::
>> CAAM-specific format. The key length for new keys is always in bytes.
>> Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
>>
>> +Trusted Keys usage: DCP
>> +-----------------------
>> +
>> +Usage::
>> +
>> + keyctl add trusted name "new keylen" ring
>> + keyctl add trusted name "load hex_blob" ring
>> + keyctl print keyid
>> +
>> +"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
>> +specific to this DCP key-blob implementation. The key length for new keys is
>> +always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
>> +
>> Encrypted Keys usage
>> --------------------
>>
>> @@ -426,3 +470,44 @@ string length.
>> privkey is the binary representation of TPM2B_PUBLIC excluding the
>> initial TPM2B header which can be reconstructed from the ASN.1 octed
>> string length.
>> +
>> +DCP Blob Format
>> +---------------
>> +
>> +The Data Co-Processor (DCP) provides hardware-bound AES keys using its
>> +AES encryption engine only. It does not provide direct key sealing/unsealing.
>> +To make DCP hardware encryption keys usable as trust source, we define
>> +our own custom format that uses a hardware-bound key to secure the sealing
>> +key stored in the key blob.
>> +
>> +Whenever a new trusted key using DCP is generated, we generate a random 128-bit
>> +blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
>> +encrypt the trusted key payload using AES-128-GCM.
>> +
>> +The BEK itself is encrypted using the hardware-bound key using the DCP's AES
>> +encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
>> +BEK-encrypted payload and authentication tag make up the blob format together
>> +with a version number, payload length and authentication tag::
>> +
>> + /*
>> + * struct dcp_blob_fmt - DCP BLOB format.
>> + *
>> + * @fmt_version: Format version, currently being %1
>> + * @blob_key: Random AES 128 key which is used to encrypt @payload,
>> + * @blob_key itself is encrypted with OTP or UNIQUE device key in
>> + * AES-128-ECB mode by DCP.
>> + * @nonce: Random nonce used for @payload encryption.
>> + * @payload_len: Length of the plain text @payload.
>> + * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
>> + * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
>> + *
>> + * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
>> + * AES_BLOCK_SIZE.
>> + */
>> + struct dcp_blob_fmt {
>> + __u8 fmt_version;
>> + __u8 blob_key[AES_KEYSIZE_128];
>> + __u8 nonce[AES_KEYSIZE_128];
>> + __le32 payload_len;
>> + __u8 payload[];
>> + } __packed;
>
> I'm thinking here given that you need to replicate the same thing that
> is in the source files. E.g. Documentation/gpu/i915.rst.
>
> The rationale would so many sources so maybe it would make sense to
> maintain this in the source code.
>
> Also this documents how to generally insert documentation inline:
> https://docs.kernel.org/doc-guide/kernel-doc.html
>
> I.e. I'm feeling that this is good time to improve scalability so that
> documentation will keep up to date. Also then backend specific patches
> mostly go to their subdirectories and not to Documentation/ subtree
> (or that would be more rare case).
>
> So a good chance to do more than just a new backend for the benefit
> of the trusted keys subsystem :-)
>
> Also, later on if something is changed e.g. in the above struct you
> don't have to do matching update to the documentation so it will save
> time too (over time).
sound good! I’ll maintain the blob format documentation to the source and insert
a reference in the documentation. Thanks for pointing that out!
Is there anything else I can improve for this patchset? I’d like to include that in v8
too and make it the last iteration of this patchset.
Thanks,
David
On Thu Mar 28, 2024 at 10:05 AM EET, David Gstir wrote:
> Jarkko,
>
> > On 27.03.2024, at 16:40, Jarkko Sakkinen <[email protected]> wrote:
> >
> > On Wed Mar 27, 2024 at 10:24 AM EET, David Gstir wrote:
> >> Update the documentation for trusted and encrypted KEYS with DCP as new
> >> trust source:
> >>
> >> - Describe security properties of DCP trust source
> >> - Describe key usage
> >> - Document blob format
> >>
> >> Co-developed-by: Richard Weinberger <[email protected]>
> >> Signed-off-by: Richard Weinberger <[email protected]>
> >> Co-developed-by: David Oberhollenzer <[email protected]>
> >> Signed-off-by: David Oberhollenzer <[email protected]>
> >> Signed-off-by: David Gstir <[email protected]>
> >> ---
> >> .../security/keys/trusted-encrypted.rst | 85 +++++++++++++++++++
> >> 1 file changed, 85 insertions(+)
> >>
> >> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> >> index e989b9802f92..81fb3540bb20 100644
> >> --- a/Documentation/security/keys/trusted-encrypted.rst
> >> +++ b/Documentation/security/keys/trusted-encrypted.rst
> >> @@ -42,6 +42,14 @@ safe.
> >> randomly generated and fused into each SoC at manufacturing time.
> >> Otherwise, a common fixed test key is used instead.
> >>
> >> + (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> >> +
> >> + Rooted to a one-time programmable key (OTP) that is generally burnt
> >> + in the on-chip fuses and is accessible to the DCP encryption engine only.
> >> + DCP provides two keys that can be used as root of trust: the OTP key
> >> + and the UNIQUE key. Default is to use the UNIQUE key, but selecting
> >> + the OTP key can be done via a module parameter (dcp_use_otp_key).
> >> +
> >> * Execution isolation
> >>
> >> (1) TPM
> >> @@ -57,6 +65,12 @@ safe.
> >>
> >> Fixed set of operations running in isolated execution environment.
> >>
> >> + (4) DCP
> >> +
> >> + Fixed set of cryptographic operations running in isolated execution
> >> + environment. Only basic blob key encryption is executed there.
> >> + The actual key sealing/unsealing is done on main processor/kernel space.
> >> +
> >> * Optional binding to platform integrity state
> >>
> >> (1) TPM
> >> @@ -79,6 +93,11 @@ safe.
> >> Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
> >> for platform integrity.
> >>
> >> + (4) DCP
> >> +
> >> + Relies on Secure/Trusted boot process (called HAB by vendor) for
> >> + platform integrity.
> >> +
> >> * Interfaces and APIs
> >>
> >> (1) TPM
> >> @@ -94,6 +113,11 @@ safe.
> >>
> >> Interface is specific to silicon vendor.
> >>
> >> + (4) DCP
> >> +
> >> + Vendor-specific API that is implemented as part of the DCP crypto driver in
> >> + ``drivers/crypto/mxs-dcp.c``.
> >> +
> >> * Threat model
> >>
> >> The strength and appropriateness of a particular trust source for a given
> >> @@ -129,6 +153,13 @@ selected trust source:
> >> CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
> >> is probed.
> >>
> >> + * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> >> +
> >> + The DCP hardware device itself does not provide a dedicated RNG interface,
> >> + so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
> >> + a dedicated hardware RNG that is independent from DCP which can be enabled
> >> + to back the kernel RNG.
> >> +
> >> Users may override this by specifying ``trusted.rng=kernel`` on the kernel
> >> command-line to override the used RNG with the kernel's random number pool.
> >>
> >> @@ -231,6 +262,19 @@ Usage::
> >> CAAM-specific format. The key length for new keys is always in bytes.
> >> Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
> >>
> >> +Trusted Keys usage: DCP
> >> +-----------------------
> >> +
> >> +Usage::
> >> +
> >> + keyctl add trusted name "new keylen" ring
> >> + keyctl add trusted name "load hex_blob" ring
> >> + keyctl print keyid
> >> +
> >> +"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
> >> +specific to this DCP key-blob implementation. The key length for new keys is
> >> +always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
> >> +
> >> Encrypted Keys usage
> >> --------------------
> >>
> >> @@ -426,3 +470,44 @@ string length.
> >> privkey is the binary representation of TPM2B_PUBLIC excluding the
> >> initial TPM2B header which can be reconstructed from the ASN.1 octed
> >> string length.
> >> +
> >> +DCP Blob Format
> >> +---------------
> >> +
> >> +The Data Co-Processor (DCP) provides hardware-bound AES keys using its
> >> +AES encryption engine only. It does not provide direct key sealing/unsealing.
> >> +To make DCP hardware encryption keys usable as trust source, we define
> >> +our own custom format that uses a hardware-bound key to secure the sealing
> >> +key stored in the key blob.
> >> +
> >> +Whenever a new trusted key using DCP is generated, we generate a random 128-bit
> >> +blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
> >> +encrypt the trusted key payload using AES-128-GCM.
> >> +
> >> +The BEK itself is encrypted using the hardware-bound key using the DCP's AES
> >> +encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
> >> +BEK-encrypted payload and authentication tag make up the blob format together
> >> +with a version number, payload length and authentication tag::
> >> +
> >> + /*
> >> + * struct dcp_blob_fmt - DCP BLOB format.
> >> + *
> >> + * @fmt_version: Format version, currently being %1
> >> + * @blob_key: Random AES 128 key which is used to encrypt @payload,
> >> + * @blob_key itself is encrypted with OTP or UNIQUE device key in
> >> + * AES-128-ECB mode by DCP.
> >> + * @nonce: Random nonce used for @payload encryption.
> >> + * @payload_len: Length of the plain text @payload.
> >> + * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
> >> + * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
> >> + *
> >> + * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
> >> + * AES_BLOCK_SIZE.
> >> + */
> >> + struct dcp_blob_fmt {
> >> + __u8 fmt_version;
> >> + __u8 blob_key[AES_KEYSIZE_128];
> >> + __u8 nonce[AES_KEYSIZE_128];
> >> + __le32 payload_len;
> >> + __u8 payload[];
> >> + } __packed;
> >
> > I'm thinking here given that you need to replicate the same thing that
> > is in the source files. E.g. Documentation/gpu/i915.rst.
> >
> > The rationale would so many sources so maybe it would make sense to
> > maintain this in the source code.
> >
> > Also this documents how to generally insert documentation inline:
> > https://docs.kernel.org/doc-guide/kernel-doc.html
> >
> > I.e. I'm feeling that this is good time to improve scalability so that
> > documentation will keep up to date. Also then backend specific patches
> > mostly go to their subdirectories and not to Documentation/ subtree
> > (or that would be more rare case).
> >
> > So a good chance to do more than just a new backend for the benefit
> > of the trusted keys subsystem :-)
> >
> > Also, later on if something is changed e.g. in the above struct you
> > don't have to do matching update to the documentation so it will save
> > time too (over time).
>
> sound good! I’ll maintain the blob format documentation to the source and insert
> a reference in the documentation. Thanks for pointing that out!
>
> Is there anything else I can improve for this patchset? I’d like to include that in v8
> too and make it the last iteration of this patchset.
Yeah, I don't enforce you to convert all the existing work to this
model, but we could use this as a reference for that work.
The patch set is overally in a pretty good shape I think :-)
BR, Jarkko
On Thu Mar 28, 2024 at 8:47 PM EET, Jarkko Sakkinen wrote:
> On Thu Mar 28, 2024 at 10:05 AM EET, David Gstir wrote:
> > Jarkko,
> >
> > > On 27.03.2024, at 16:40, Jarkko Sakkinen <[email protected]> wrote:
> > >
> > > On Wed Mar 27, 2024 at 10:24 AM EET, David Gstir wrote:
> > >> Update the documentation for trusted and encrypted KEYS with DCP as new
> > >> trust source:
> > >>
> > >> - Describe security properties of DCP trust source
> > >> - Describe key usage
> > >> - Document blob format
> > >>
> > >> Co-developed-by: Richard Weinberger <[email protected]>
> > >> Signed-off-by: Richard Weinberger <[email protected]>
> > >> Co-developed-by: David Oberhollenzer <[email protected]>
> > >> Signed-off-by: David Oberhollenzer <[email protected]>
> > >> Signed-off-by: David Gstir <[email protected]>
> > >> ---
> > >> .../security/keys/trusted-encrypted.rst | 85 +++++++++++++++++++
> > >> 1 file changed, 85 insertions(+)
> > >>
> > >> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> > >> index e989b9802f92..81fb3540bb20 100644
> > >> --- a/Documentation/security/keys/trusted-encrypted.rst
> > >> +++ b/Documentation/security/keys/trusted-encrypted.rst
> > >> @@ -42,6 +42,14 @@ safe.
> > >> randomly generated and fused into each SoC at manufacturing time.
> > >> Otherwise, a common fixed test key is used instead.
> > >>
> > >> + (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> > >> +
> > >> + Rooted to a one-time programmable key (OTP) that is generally burnt
> > >> + in the on-chip fuses and is accessible to the DCP encryption engine only.
> > >> + DCP provides two keys that can be used as root of trust: the OTP key
> > >> + and the UNIQUE key. Default is to use the UNIQUE key, but selecting
> > >> + the OTP key can be done via a module parameter (dcp_use_otp_key).
> > >> +
> > >> * Execution isolation
> > >>
> > >> (1) TPM
> > >> @@ -57,6 +65,12 @@ safe.
> > >>
> > >> Fixed set of operations running in isolated execution environment.
> > >>
> > >> + (4) DCP
> > >> +
> > >> + Fixed set of cryptographic operations running in isolated execution
> > >> + environment. Only basic blob key encryption is executed there.
> > >> + The actual key sealing/unsealing is done on main processor/kernel space.
> > >> +
> > >> * Optional binding to platform integrity state
> > >>
> > >> (1) TPM
> > >> @@ -79,6 +93,11 @@ safe.
> > >> Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
> > >> for platform integrity.
> > >>
> > >> + (4) DCP
> > >> +
> > >> + Relies on Secure/Trusted boot process (called HAB by vendor) for
> > >> + platform integrity.
> > >> +
> > >> * Interfaces and APIs
> > >>
> > >> (1) TPM
> > >> @@ -94,6 +113,11 @@ safe.
> > >>
> > >> Interface is specific to silicon vendor.
> > >>
> > >> + (4) DCP
> > >> +
> > >> + Vendor-specific API that is implemented as part of the DCP crypto driver in
> > >> + ``drivers/crypto/mxs-dcp.c``.
> > >> +
> > >> * Threat model
> > >>
> > >> The strength and appropriateness of a particular trust source for a given
> > >> @@ -129,6 +153,13 @@ selected trust source:
> > >> CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
> > >> is probed.
> > >>
> > >> + * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> > >> +
> > >> + The DCP hardware device itself does not provide a dedicated RNG interface,
> > >> + so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
> > >> + a dedicated hardware RNG that is independent from DCP which can be enabled
> > >> + to back the kernel RNG.
> > >> +
> > >> Users may override this by specifying ``trusted.rng=kernel`` on the kernel
> > >> command-line to override the used RNG with the kernel's random number pool.
> > >>
> > >> @@ -231,6 +262,19 @@ Usage::
> > >> CAAM-specific format. The key length for new keys is always in bytes.
> > >> Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
> > >>
> > >> +Trusted Keys usage: DCP
> > >> +-----------------------
> > >> +
> > >> +Usage::
> > >> +
> > >> + keyctl add trusted name "new keylen" ring
> > >> + keyctl add trusted name "load hex_blob" ring
> > >> + keyctl print keyid
> > >> +
> > >> +"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
> > >> +specific to this DCP key-blob implementation. The key length for new keys is
> > >> +always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
> > >> +
> > >> Encrypted Keys usage
> > >> --------------------
> > >>
> > >> @@ -426,3 +470,44 @@ string length.
> > >> privkey is the binary representation of TPM2B_PUBLIC excluding the
> > >> initial TPM2B header which can be reconstructed from the ASN.1 octed
> > >> string length.
> > >> +
> > >> +DCP Blob Format
> > >> +---------------
> > >> +
> > >> +The Data Co-Processor (DCP) provides hardware-bound AES keys using its
> > >> +AES encryption engine only. It does not provide direct key sealing/unsealing.
> > >> +To make DCP hardware encryption keys usable as trust source, we define
> > >> +our own custom format that uses a hardware-bound key to secure the sealing
> > >> +key stored in the key blob.
> > >> +
> > >> +Whenever a new trusted key using DCP is generated, we generate a random 128-bit
> > >> +blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
> > >> +encrypt the trusted key payload using AES-128-GCM.
> > >> +
> > >> +The BEK itself is encrypted using the hardware-bound key using the DCP's AES
> > >> +encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
> > >> +BEK-encrypted payload and authentication tag make up the blob format together
> > >> +with a version number, payload length and authentication tag::
> > >> +
> > >> + /*
> > >> + * struct dcp_blob_fmt - DCP BLOB format.
> > >> + *
> > >> + * @fmt_version: Format version, currently being %1
> > >> + * @blob_key: Random AES 128 key which is used to encrypt @payload,
> > >> + * @blob_key itself is encrypted with OTP or UNIQUE device key in
> > >> + * AES-128-ECB mode by DCP.
> > >> + * @nonce: Random nonce used for @payload encryption.
> > >> + * @payload_len: Length of the plain text @payload.
> > >> + * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
> > >> + * GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
> > >> + *
> > >> + * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
> > >> + * AES_BLOCK_SIZE.
> > >> + */
> > >> + struct dcp_blob_fmt {
> > >> + __u8 fmt_version;
> > >> + __u8 blob_key[AES_KEYSIZE_128];
> > >> + __u8 nonce[AES_KEYSIZE_128];
> > >> + __le32 payload_len;
> > >> + __u8 payload[];
> > >> + } __packed;
> > >
> > > I'm thinking here given that you need to replicate the same thing that
> > > is in the source files. E.g. Documentation/gpu/i915.rst.
> > >
> > > The rationale would so many sources so maybe it would make sense to
> > > maintain this in the source code.
> > >
> > > Also this documents how to generally insert documentation inline:
> > > https://docs.kernel.org/doc-guide/kernel-doc.html
> > >
> > > I.e. I'm feeling that this is good time to improve scalability so that
> > > documentation will keep up to date. Also then backend specific patches
> > > mostly go to their subdirectories and not to Documentation/ subtree
> > > (or that would be more rare case).
> > >
> > > So a good chance to do more than just a new backend for the benefit
> > > of the trusted keys subsystem :-)
> > >
> > > Also, later on if something is changed e.g. in the above struct you
> > > don't have to do matching update to the documentation so it will save
> > > time too (over time).
> >
> > sound good! I’ll maintain the blob format documentation to the source and insert
> > a reference in the documentation. Thanks for pointing that out!
> >
> > Is there anything else I can improve for this patchset? I’d like to include that in v8
> > too and make it the last iteration of this patchset.
>
> Yeah, I don't enforce you to convert all the existing work to this
> model, but we could use this as a reference for that work.
I mean that way documentation update will become more natural part of
the code update and less frustrating to do which usually encourages
to document stuff better and also later on tweak and improve it.
So yeah I feel that GPU documentation in kernel is doing lot's of things
right, and other subsystems should follow. I.e. it is good reference
model for trusted keys documentation, and said I'm cool with realizing
this for only this new key type :-) Otherwise, finishing this patch set
will torture for you and also for me if it tries to fix everything.
BR, Jarkko