[PATCH 5.4.y] crypto: atmel-sha204a - Set hwrng quality to lowest possible

[PATCH 5.4.y] crypto: atmel-sha204a - Set hwrng quality to lowest possible

[Marek Behún]

commit 8006aff15516a170640239c5a8e6696c0ba18d8e upstream.

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")
Cc: <stable@vger.kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[ rebased for 5.4 ]
Signed-off-by: Marek Behún <kabel@kernel.org>
---
 drivers/crypto/atmel-sha204a.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index c96c14e7dab1..0ef92109ce22 100644
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -107,7 +107,12 @@ 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;
-	i2c_priv->hwrng.quality = 1024;
+
+	/*
+	 * 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)
-- 
2.49.0