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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777371326; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=xcy635DpKKoCVUN6XKiv2266UoWMk9NqTJ3mH2R1Q9g=; b=pX/HKCiZvez7ezlxL+P09TKTq1bX23uyrhEP1GTt7e4+HtRS4vGbYfkhGlMpyn9E9YXADJ ZlmVYW3uP/7V0fXEqXjzrMYSFt4JA4B8ERzYvVMVky2oY6jGEEwsokJ4oQTlD17TE6ydOP dIisVQTOwHm6EoYRaL8f4SBby9PNP8c= From: Thorsten Blum To: Thorsten Blum , Herbert Xu , "David S. Miller" , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , =?UTF-8?q?Marek=20Beh=C3=BAn?= , Linus Walleij , Ard Biesheuvel Cc: stable@vger.kernel.org, linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] crypto: atmel-sha204a - drop hwrng quality reduction for ATSHA204A Date: Tue, 28 Apr 2026 12:14:32 +0200 Message-ID: <20260428101430.514838-3-thorsten.blum@linux.dev> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3773; i=thorsten.blum@linux.dev; h=from:subject; bh=j1nd45mg4g3EXUjYAzfoYk5UWhyibVn267xhc4o9T+8=; b=owGbwMvMwCUWt7pQ4caZUj3G02pJDJkfOtpmOE333BNo027uvc7sukDnxj2T3k90Xs8dYXPtS 6HjpPVHO0pZGMS4GGTFFFkezPoxw7e0pnKTScROmDmsTCBDGLg4BWAi714y/I+3mbHCaWF3Q+oM h2bRG7OeuDiv83qfkHNfMsGxbNOL+MMM/11+ufdujdnVN7dsI+fXI0rRodPVbru/f2N7wO3a5st yt1gB X-Developer-Key: i=thorsten.blum@linux.dev; a=openpgp; fpr=1D60735E8AEF3BE473B69D84733678FD8DFEEAD4 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260428_031530_484959_E9823FEC X-CRM114-Status: GOOD ( 15.93 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Commit 8006aff15516 ("crypto: atmel-sha204a - Set hwrng quality to lowest possible") reduced the hwrng quality to 1 based on a review by Bill Cox [1]. However, despite its title, the review only tested the ATSHA204, not the ATSHA204A. In the same thread, Atmel engineer Landon Cox wrote "this behavior has been eliminated entirely"[2] in the ATSHA204A and "this problem does not affect the ATECC108 or the ATECC108A (or the ATSHA204A)"[3]. According to the official ATSHA204A datasheet [4], the device contains a high-quality hardware RNG that combines its output with an internal seed value stored in EEPROM or SRAM to generate random numbers. The device also implements all security functions using SHA-256, and the driver uses the chip's Random command in seed-update mode. Keep 'quality = 1' for ATSHA204, but drop the explicit hwrng quality reduction for ATSHA204A and fall back to the hwrng core default. [1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html [2] https://www.metzdowd.com/pipermail/cryptography/2014-December/023852.html [3] https://www.metzdowd.com/pipermail/cryptography/2014-December/023886.html [4] https://ww1.microchip.com/downloads/en/DeviceDoc/ATSHA204A-Data-Sheet-40002025A.pdf Fixes: 8006aff15516 ("crypto: atmel-sha204a - Set hwrng quality to lowest possible") Cc: stable@vger.kernel.org Signed-off-by: Thorsten Blum --- Changes in v2: - Drop the enum and dereference match data if needed as suggested by Ard - Keep the review comment - v1: https://lore.kernel.org/lkml/20260427124030.315590-3-thorsten.blum@linux.dev/ --- drivers/crypto/atmel-sha204a.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c index dbb39ed0cea1..a8c1b00b12f5 100644 --- a/drivers/crypto/atmel-sha204a.c +++ b/drivers/crypto/atmel-sha204a.c @@ -19,6 +19,12 @@ #include #include "atmel-i2c.h" +/* + * According to review by Bill Cox [1], the ATSHA204 has very low entropy. + * [1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html + */ +static const unsigned short atsha204_quality = 1; + static void atmel_sha204a_rng_done(struct atmel_i2c_work_data *work_data, void *areq, int status) { @@ -158,6 +164,7 @@ static const struct attribute_group atmel_sha204a_groups = { static int atmel_sha204a_probe(struct i2c_client *client) { struct atmel_i2c_client_priv *i2c_priv; + const unsigned short *quality; int ret; ret = atmel_i2c_probe(client); @@ -171,11 +178,9 @@ 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; + quality = i2c_get_match_data(client); + if (quality) + i2c_priv->hwrng.quality = *quality; ret = devm_hwrng_register(&client->dev, &i2c_priv->hwrng); if (ret) @@ -203,14 +208,14 @@ static void atmel_sha204a_remove(struct i2c_client *client) } static const struct of_device_id atmel_sha204a_dt_ids[] __maybe_unused = { - { .compatible = "atmel,atsha204", }, + { .compatible = "atmel,atsha204", .data = &atsha204_quality }, { .compatible = "atmel,atsha204a", }, { /* sentinel */ } }; MODULE_DEVICE_TABLE(of, atmel_sha204a_dt_ids); static const struct i2c_device_id atmel_sha204a_id[] = { - { "atsha204" }, + { "atsha204", (kernel_ulong_t)&atsha204_quality }, { "atsha204a" }, { /* sentinel */ } };