[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <20191015124702.633-1-jarkko.sakkinen@linux.intel.com>
Date: Tue, 15 Oct 2019 15:47:02 +0300
From: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To: linux-integrity@...r.kernel.org
Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
David Safford <david.safford@...com>,
Pascal Van Leeuwen <pvanleeuwen@...imatrix.com>,
James Bottomley <James.Bottomley@...senPartnership.com>,
Peter Huewe <peterhuewe@....de>,
Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] tpm: Salt tpm_get_random() result with get_random_bytes()
Salt the result that comes from the TPM RNG with random bytes from the
kernel RNG. This will allow to use tpm_get_random() as a substitute for
get_random_bytes(). TPM could have a bug (making results predicatable),
backdoor or even an inteposer in the bus. Salting gives protections
against these concerns.
Cc: David Safford <david.safford@...com>
Cc: Pascal Van Leeuwen <pvanleeuwen@...imatrix.com>
Cc: James Bottomley <James.Bottomley@...senPartnership.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
---
drivers/char/tpm/tpm-interface.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 7f105490604c..a135b1cd5a17 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -22,6 +22,7 @@
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/mutex.h>
+#include <linux/random.h>
#include <linux/spinlock.h>
#include <linux/suspend.h>
#include <linux/freezer.h>
@@ -431,16 +432,24 @@ int tpm_pm_resume(struct device *dev)
EXPORT_SYMBOL_GPL(tpm_pm_resume);
/**
- * tpm_get_random() - get random bytes from the TPM's RNG
+ * tpm_get_random() - Get random bytes from the TPM's RNG
* @chip: a &struct tpm_chip instance, %NULL for the default chip
* @out: destination buffer for the random bytes
* @max: the max number of bytes to write to @out
*
- * Return: number of random bytes read or a negative error value.
+ * Get random bytes from the TPM's RNG and salt the result with the same amount
+ * of bytes from the kernel RNG. Salting allows to call this function as a
+ * substitute for get_random_bytes() where appropriate.
+ *
+ * Return:
+ * number of random bytes on success,
+ * -errno on error
*/
int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max)
{
+ u8 salt[TPM_MAX_RNG_DATA];
int rc;
+ int i;
if (!out || max > TPM_MAX_RNG_DATA)
return -EINVAL;
@@ -455,6 +464,14 @@ int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max)
rc = tpm1_get_random(chip, out, max);
tpm_put_ops(chip);
+
+ if (rc > 0) {
+ get_random_bytes(salt, rc);
+
+ for (i = 0; i < rc; i++)
+ out[i] ^= salt[i];
+ }
+
return rc;
}
EXPORT_SYMBOL_GPL(tpm_get_random);
--
2.20.1
Powered by blists - more mailing lists