linux-kernel - [PATCH] tpm: Add module parameter for hwrng quality.

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Date:   Fri,  8 Jun 2018 14:54:38 +0800
From:   Louis Collard <louiscollard@...omium.org>
To:     linux-integrity@...r.kernel.org
Cc:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, apronin@...omium.org
Subject: [PATCH] tpm: Add module parameter for hwrng quality.

It is now possible for drivers to easily specify a hwrng quality, however
most do not currently do this, and in cases where they do, it may be
desirable to override the driver-specified value with a user-specified
one. This patch adds a parameter to set or override the hwrng quality.

Signed-off-by: Louis Collard <louiscollard@...omium.org>
---
 drivers/char/tpm/tpm-chip.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 0a62c19937b6..4def49cfc634 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -33,6 +33,11 @@
 DEFINE_IDR(dev_nums_idr);
 static DEFINE_MUTEX(idr_lock);
 
+static short override_rng_quality = -1;
+module_param(override_rng_quality, short, 0644);
+MODULE_PARM_DESC(override_rng_quality,
+		 "tpm-rng quality (overrides values provided by drivers)");
+
 struct class *tpm_class;
 struct class *tpmrm_class;
 dev_t tpm_devt;
@@ -409,6 +414,13 @@ static int tpm_add_hwrng(struct tpm_chip *chip)
 		 "tpm-rng-%d", chip->dev_num);
 	chip->hwrng.name = chip->hwrng_name;
 	chip->hwrng.read = tpm_hwrng_read;
+	if (override_rng_quality > -1) {
+		dev_info(&chip->dev,
+			 "Overriding hwrng quality for %s: driver default=%d, override=%d",
+			 chip->hwrng.name, chip->hwrng.quality,
+			 override_rng_quality);
+		chip->hwrng.quality = override_rng_quality;
+	}
 	return hwrng_register(&chip->hwrng);
 }
 
-- 
2.13.5