linux-kernel - [PATCH] security/keys/trusted: Allow operation without hardware TPM

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Message-ID: <155295271345.1945351.6465460744078693578.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Mon, 18 Mar 2019 16:45:13 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     jarkko.sakkinen@...ux.intel.com
Cc:     Roberto Sassu <roberto.sassu@...wei.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org
Subject: [PATCH] security/keys/trusted: Allow operation without hardware TPM

Rather than fail initialization of the trusted.ko module, arrange for
the module to load, but rely on trusted_instantiate() to fail
trusted-key operations.

Fixes: 240730437deb ("KEYS: trusted: explicitly use tpm_chip structure...")
Cc: Roberto Sassu <roberto.sassu@...wei.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc: James Bottomley <jejb@...ux.ibm.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc: Mimi Zohar <zohar@...ux.ibm.com>
Cc: David Howells <dhowells@...hat.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 security/keys/trusted.c |   21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index bcc9c6ead7fd..d959597a688e 100644
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -45,6 +45,13 @@ struct sdesc {
 static struct crypto_shash *hashalg;
 static struct crypto_shash *hmacalg;
 
+static struct device *chip_dev(struct tpm_chip *chip)
+{
+	if (chip)
+		return &chip->dev;
+	return NULL;
+}
+
 static struct sdesc *init_sdesc(struct crypto_shash *alg)
 {
 	struct sdesc *sdesc;
@@ -1224,6 +1231,14 @@ static int __init init_digests(void)
 	int ret;
 	int i;
 
+	/*
+	 * Hardware tpm operations are disabled, but allow the software
+	 * module to initialize, and depend on trusted_instantiate() to
+	 * fail any attempts to access the missing hardware.
+	 */
+	if (!chip)
+		return 0;
+
 	ret = tpm_get_random(chip, digest, TPM_MAX_DIGEST_SIZE);
 	if (ret < 0)
 		return ret;
@@ -1246,8 +1261,6 @@ static int __init init_trusted(void)
 	int ret;
 
 	chip = tpm_default_chip();
-	if (!chip)
-		return -ENOENT;
 	ret = init_digests();
 	if (ret < 0)
 		goto err_put;
@@ -1263,13 +1276,13 @@ static int __init init_trusted(void)
 err_free:
 	kfree(digests);
 err_put:
-	put_device(&chip->dev);
+	put_device(chip_dev(chip));
 	return ret;
 }
 
 static void __exit cleanup_trusted(void)
 {
-	put_device(&chip->dev);
+	put_device(chip_dev(chip));
 	kfree(digests);
 	trusted_shash_release();
 	unregister_key_type(&key_type_trusted);