linux-kernel - [PATCH] crypto: atmel-sha204a - Set hwrng quality to lowest possible

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Message-ID: <20250422095718.17360-1-kabel@kernel.org>
Date: Tue, 22 Apr 2025 11:57:18 +0200
From: Marek Behún <kabel@...nel.org>
To: linux-crypto@...r.kernel.org
Cc: Marek Behún <kabel@...nel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Ard Biesheuvel <ardb@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] crypto: atmel-sha204a - Set hwrng quality to lowest possible

According to the review by Bill Cox [1], the Atmel SHA204A random number
generator produces random numbers with very low entropy.

Set the lowest possible entropy for this chip just to be safe.

[1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html

Fixes: da001fb651b00e1d ("crypto: atmel-i2c - add support for SHA204A random number generator")
Signed-off-by: Marek Behún <kabel@...nel.org>
---
 drivers/crypto/atmel-sha204a.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index 75bebec2c757..0fcf4a39de27 100644
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -163,6 +163,12 @@ static int atmel_sha204a_probe(struct i2c_client *client)
 	i2c_priv->hwrng.name = dev_name(&client->dev);
 	i2c_priv->hwrng.read = atmel_sha204a_rng_read;
 
+	/*
+	 * According to review by Bill Cox [1], this HWRNG has very low entropy.
+	 * [1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html
+	 */
+	i2c_priv->hwrng.quality = 1;
+
 	ret = devm_hwrng_register(&client->dev, &i2c_priv->hwrng);
 	if (ret)
 		dev_warn(&client->dev, "failed to register RNG (%d)\n", ret);
-- 
2.49.0