Re: [PATCH v2] KEYS: trusted: Debugging as a feature

Jarkko Sakkinen
2026-04-08T08:27:01Z

On Mon, Apr 06, 2026 at 10:42:00PM -0400, Nayna Jain wrote:
>
> On 3/24/26 7:00 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.
> >
> > Traces, when actually needed, can be easily enabled by providing
> > trusted.dyndbg='+p' in the kernel command-line.
> >
> > Cc: Srish Srinivasan <ssrish@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/
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > ---
> > v2:
> > - Implement for all trusted keys backends.
> > - Add HAVE_TRUSTED_KEYS_DEBUG as it is a good practice despite full
> > coverage.
> > ---
> > include/keys/trusted-type.h | 18 +++++-------
> > security/keys/trusted-keys/Kconfig | 19 ++++++++++++
> > security/keys/trusted-keys/trusted_caam.c | 4 +--
> > security/keys/trusted-keys/trusted_tpm1.c | 36 +++++++++++------------
> > 4 files changed, 46 insertions(+), 31 deletions(-)
> >
> > diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
> > index 03527162613f..620a1f890b6b 100644
> > --- a/include/keys/trusted-type.h
> > +++ b/include/keys/trusted-type.h
> > @@ -83,18 +83,16 @@ struct trusted_key_source {
> > extern struct key_type key_type_trusted;
> > -#define TRUSTED_DEBUG 0
> > -
> > -#if TRUSTED_DEBUG
> > +#ifdef CONFIG_TRUSTED_KEYS_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);
> > + 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..2ad9ba0e03f1 100644
> > --- a/security/keys/trusted-keys/Kconfig
> > +++ b/security/keys/trusted-keys/Kconfig
> > @@ -1,10 +1,25 @@
> > 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 keys backends and core code that support debug dumps
> > + can opt-in that feature here. Dumps 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'.
>
> Would it be good idea to add an explicit note/warning:
>
>
> NOTE: This option is intended for debugging purposes only. Do not enable on
> production systems as debug output may expose sensitive cryptographic
> material.
> If you are unsure, say N.
>
> Apart from this, looks good to me.
>
> Reviewed-by: Nayna Jain <nayna@linux.ibm.com>

Thank, I'll add your tag but would you mind quickly screening v3 again
where I add "trusted.debug=0|1". And yes, your suggestion about extra
warning makes sense.

Let's make this safe as possible. Mistakes do happen... and then those
measures pay off :-)

BR, Jarkko