Re: [PATCH v4] KEYS: trusted: Debugging as a feature

[Nayna Jain <nayna@linux.ibm.com>]

On 4/15/26 7:12 AM, Jarkko Sakkinen wrote:
> TPM_DEBUG, and other similar flags, are a non-standard way to specify a
> feature in Linux kernel. Introduce CONFIG_TRUSTED_KEYS_DEBUG for trusted
> keys, and use it to replace these ad-hoc feature flags.
>
> Given that trusted keys debug dumps can contain sensitive data, harden the
> feature as follows:
>
> 1. In the Kconfig description postulate that pr_debug() statements must be
>     used.
> 2. Use pr_debug() statements in TPM 1.x driver to print the protocol dump.
> 3. Require trusted.debug=1 on the kernel command line (default: 0) to
>     activate dumps at runtime, even when CONFIG_TRUSTED_KEYS_DEBUG=y.
>
> Traces, when actually needed, can be easily enabled by providing
> trusted.dyndbg='+p' and trusted.debug=1 in the kernel command-line.

Thanks for adding the documentation.

Reviewed-by: Nayna Jain <nayna@linux.ibm.com>

>
> Reported-by: Nayna Jain <nayna@linux.ibm.com>
> Closes: https://lore.kernel.org/all/7f8b8478-5cd8-4d97-bfd0-341fd5cf10f9@linux.ibm.com/
> Reviewed-by: Nayna Jain <nayna@linux.ibm.com>
> Tested-by: Srish Srinivasan <ssrish@linux.ibm.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> v4:
> - Added kernel parameter documentation.t
> - Added tags from Srishand and Nayna.
> - Sanity check round. This version will be applied unless there is
>    something specific to address.
> v3:
> - Add kernel-command line option for enabling the traces.
> - Add safety information to the Kconfig entry.
> v2:
> - Implement for all trusted keys backends.
> - Add HAVE_TRUSTED_KEYS_DEBUG as it is a good practice despite full
>    coverage.
> ---
>   .../admin-guide/kernel-parameters.txt         | 16 +++++++
>   include/keys/trusted-type.h                   | 21 +++++----
>   security/keys/trusted-keys/Kconfig            | 23 ++++++++++
>   security/keys/trusted-keys/trusted_caam.c     |  7 ++-
>   security/keys/trusted-keys/trusted_core.c     |  6 +++
>   security/keys/trusted-keys/trusted_tpm1.c     | 44 +++++++++++--------
>   6 files changed, 87 insertions(+), 30 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f2ce1f4975c1..f1515668c8ab 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7917,6 +7917,22 @@ Kernel parameters
>   			first trust source as a backend which is initialized
>   			successfully during iteration.
>   
> +	trusted.debug=	[KEYS]
> +			Format: <bool>
> +			Enable trusted keys debug traces at runtime when
> +			CONFIG_TRUSTED_KEYS_DEBUG=y.
> +
> +			To make the traces visible after enabling the option,
> +			use trusted.dyndbg='+p' as needed. By convention,
> +			the subsystem uses pr_debug() for these traces.
> +
> +			SAFETY: The traces can leak sensitive data, so be
> +			cautious before enabling this. They remain inactive
> +			unless this parameter is set this option to  a true
> +			value.
> +
> +			Default: false
> +
>   	trusted.rng=	[KEYS]
>   			Format: <string>
>   			The RNG used to generate key material for trusted keys.
> diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
> index 03527162613f..9f9940482da4 100644
> --- a/include/keys/trusted-type.h
> +++ b/include/keys/trusted-type.h
> @@ -83,18 +83,21 @@ struct trusted_key_source {
>   
>   extern struct key_type key_type_trusted;
>   
> -#define TRUSTED_DEBUG 0
> +#ifdef CONFIG_TRUSTED_KEYS_DEBUG
> +extern bool trusted_debug;
>   
> -#if TRUSTED_DEBUG
>   static inline void dump_payload(struct trusted_key_payload *p)
>   {
> -	pr_info("key_len %d\n", p->key_len);
> -	print_hex_dump(KERN_INFO, "key ", DUMP_PREFIX_NONE,
> -		       16, 1, p->key, p->key_len, 0);
> -	pr_info("bloblen %d\n", p->blob_len);
> -	print_hex_dump(KERN_INFO, "blob ", DUMP_PREFIX_NONE,
> -		       16, 1, p->blob, p->blob_len, 0);
> -	pr_info("migratable %d\n", p->migratable);
> +	if (!trusted_debug)
> +		return;
> +
> +	pr_debug("key_len %d\n", p->key_len);
> +	print_hex_dump_debug("key ", DUMP_PREFIX_NONE,
> +			     16, 1, p->key, p->key_len, 0);
> +	pr_debug("bloblen %d\n", p->blob_len);
> +	print_hex_dump_debug("blob ", DUMP_PREFIX_NONE,
> +			     16, 1, p->blob, p->blob_len, 0);
> +	pr_debug("migratable %d\n", p->migratable);
>   }
>   #else
>   static inline void dump_payload(struct trusted_key_payload *p)
> diff --git a/security/keys/trusted-keys/Kconfig b/security/keys/trusted-keys/Kconfig
> index 9e00482d886a..e5a4a53aeab2 100644
> --- a/security/keys/trusted-keys/Kconfig
> +++ b/security/keys/trusted-keys/Kconfig
> @@ -1,10 +1,29 @@
>   config HAVE_TRUSTED_KEYS
>   	bool
>   
> +config HAVE_TRUSTED_KEYS_DEBUG
> +	bool
> +
> +config TRUSTED_KEYS_DEBUG
> +	bool "Debug trusted keys"
> +	depends on HAVE_TRUSTED_KEYS_DEBUG
> +	default n
> +	help
> +	  Trusted key backends and core code that support debug traces can
> +	  opt-in that feature here. Traces must only use debug level output, as
> +	  sensitive data may pass by. In the kernel-command line traces can be
> +	  enabled via trusted.dyndbg='+p'.
> +
> +	  SAFETY: Debug dumps are inactive at runtime until trusted.debug is set
> +	  to a true value on the kernel command-line. Use at your utmost
> +	  consideration when enabling this feature on a production build. The
> +	  general advice is not to do this.
> +
>   config TRUSTED_KEYS_TPM
>   	bool "TPM-based trusted keys"
>   	depends on TCG_TPM >= TRUSTED_KEYS
>   	default y
> +	select HAVE_TRUSTED_KEYS_DEBUG
>   	select CRYPTO_HASH_INFO
>   	select CRYPTO_LIB_SHA1
>   	select CRYPTO_LIB_UTILS
> @@ -23,6 +42,7 @@ config TRUSTED_KEYS_TEE
>   	bool "TEE-based trusted keys"
>   	depends on TEE >= TRUSTED_KEYS
>   	default y
> +	select HAVE_TRUSTED_KEYS_DEBUG
>   	select HAVE_TRUSTED_KEYS
>   	help
>   	  Enable use of the Trusted Execution Environment (TEE) as trusted
> @@ -33,6 +53,7 @@ config TRUSTED_KEYS_CAAM
>   	depends on CRYPTO_DEV_FSL_CAAM_JR >= TRUSTED_KEYS
>   	select CRYPTO_DEV_FSL_CAAM_BLOB_GEN
>   	default y
> +	select HAVE_TRUSTED_KEYS_DEBUG
>   	select HAVE_TRUSTED_KEYS
>   	help
>   	  Enable use of NXP's Cryptographic Accelerator and Assurance Module
> @@ -42,6 +63,7 @@ config TRUSTED_KEYS_DCP
>   	bool "DCP-based trusted keys"
>   	depends on CRYPTO_DEV_MXS_DCP >= TRUSTED_KEYS
>   	default y
> +	select HAVE_TRUSTED_KEYS_DEBUG
>   	select HAVE_TRUSTED_KEYS
>   	help
>   	  Enable use of NXP's DCP (Data Co-Processor) as trusted key backend.
> @@ -50,6 +72,7 @@ config TRUSTED_KEYS_PKWM
>   	bool "PKWM-based trusted keys"
>   	depends on PSERIES_PLPKS >= TRUSTED_KEYS
>   	default y
> +	select HAVE_TRUSTED_KEYS_DEBUG
>   	select HAVE_TRUSTED_KEYS
>   	help
>   	  Enable use of IBM PowerVM Key Wrapping Module (PKWM) as a trusted key backend.
> diff --git a/security/keys/trusted-keys/trusted_caam.c b/security/keys/trusted-keys/trusted_caam.c
> index 601943ce0d60..6a33dbf2a7f5 100644
> --- a/security/keys/trusted-keys/trusted_caam.c
> +++ b/security/keys/trusted-keys/trusted_caam.c
> @@ -28,10 +28,13 @@ static const match_table_t key_tokens = {
>   	{opt_err, NULL}
>   };
>   
> -#ifdef CAAM_DEBUG
> +#ifdef CONFIG_TRUSTED_KEYS_DEBUG
>   static inline void dump_options(const struct caam_pkey_info *pkey_info)
>   {
> -	pr_info("key encryption algo %d\n", pkey_info->key_enc_algo);
> +	if (!trusted_debug)
> +		return;
> +
> +	pr_debug("key encryption algo %d\n", pkey_info->key_enc_algo);
>   }
>   #else
>   static inline void dump_options(const struct caam_pkey_info *pkey_info)
> diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
> index 0b142d941cd2..6aed17bee09d 100644
> --- a/security/keys/trusted-keys/trusted_core.c
> +++ b/security/keys/trusted-keys/trusted_core.c
> @@ -31,6 +31,12 @@ static char *trusted_rng = "default";
>   module_param_named(rng, trusted_rng, charp, 0);
>   MODULE_PARM_DESC(rng, "Select trusted key RNG");
>   
> +#ifdef CONFIG_TRUSTED_KEYS_DEBUG
> +bool trusted_debug;
> +module_param_named(debug, trusted_debug, bool, 0);
> +MODULE_PARM_DESC(debug, "Enable trusted keys debug traces (default: 0)");
> +#endif
> +
>   static char *trusted_key_source;
>   module_param_named(source, trusted_key_source, charp, 0);
>   MODULE_PARM_DESC(source, "Select trusted keys source (tpm, tee, caam, dcp or pkwm)");
> diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
> index 6ea728f1eae6..13513819991e 100644
> --- a/security/keys/trusted-keys/trusted_tpm1.c
> +++ b/security/keys/trusted-keys/trusted_tpm1.c
> @@ -46,38 +46,44 @@ enum {
>   	SRK_keytype = 4
>   };
>   
> -#define TPM_DEBUG 0
> -
> -#if TPM_DEBUG
> +#ifdef CONFIG_TRUSTED_KEYS_DEBUG
>   static inline void dump_options(struct trusted_key_options *o)
>   {
> -	pr_info("sealing key type %d\n", o->keytype);
> -	pr_info("sealing key handle %0X\n", o->keyhandle);
> -	pr_info("pcrlock %d\n", o->pcrlock);
> -	pr_info("pcrinfo %d\n", o->pcrinfo_len);
> -	print_hex_dump(KERN_INFO, "pcrinfo ", DUMP_PREFIX_NONE,
> -		       16, 1, o->pcrinfo, o->pcrinfo_len, 0);
> +	if (!trusted_debug)
> +		return;
> +
> +	pr_debug("sealing key type %d\n", o->keytype);
> +	pr_debug("sealing key handle %0X\n", o->keyhandle);
> +	pr_debug("pcrlock %d\n", o->pcrlock);
> +	pr_debug("pcrinfo %d\n", o->pcrinfo_len);
> +	print_hex_dump_debug("pcrinfo ", DUMP_PREFIX_NONE,
> +			     16, 1, o->pcrinfo, o->pcrinfo_len, 0);
>   }
>   
>   static inline void dump_sess(struct osapsess *s)
>   {
> -	print_hex_dump(KERN_INFO, "trusted-key: handle ", DUMP_PREFIX_NONE,
> -		       16, 1, &s->handle, 4, 0);
> -	pr_info("secret:\n");
> -	print_hex_dump(KERN_INFO, "", DUMP_PREFIX_NONE,
> -		       16, 1, &s->secret, SHA1_DIGEST_SIZE, 0);
> -	pr_info("trusted-key: enonce:\n");
> -	print_hex_dump(KERN_INFO, "", DUMP_PREFIX_NONE,
> -		       16, 1, &s->enonce, SHA1_DIGEST_SIZE, 0);
> +	if (!trusted_debug)
> +		return;
> +
> +	print_hex_dump_debug("trusted-key: handle ", DUMP_PREFIX_NONE,
> +			     16, 1, &s->handle, 4, 0);
> +	pr_debug("secret:\n");
> +	print_hex_dump_debug("", DUMP_PREFIX_NONE,
> +			     16, 1, &s->secret, SHA1_DIGEST_SIZE, 0);
> +	pr_debug("trusted-key: enonce:\n");
> +	print_hex_dump_debug("", DUMP_PREFIX_NONE,
> +			     16, 1, &s->enonce, SHA1_DIGEST_SIZE, 0);
>   }
>   
>   static inline void dump_tpm_buf(unsigned char *buf)
>   {
>   	int len;
>   
> -	pr_info("\ntpm buffer\n");
> +	if (!trusted_debug)
> +		return;
> +	pr_debug("\ntpm buffer\n");
>   	len = LOAD32(buf, TPM_SIZE_OFFSET);
> -	print_hex_dump(KERN_INFO, "", DUMP_PREFIX_NONE, 16, 1, buf, len, 0);
> +	print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, buf, len, 0);
>   }
>   #else
>   static inline void dump_options(struct trusted_key_options *o)