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Thu, 23 Apr 2026 05:25:37 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Thu, 23 Apr 2026 11:25:16 +0200 From: "Ard Biesheuvel" To: "Lothar Rubusch" , "Herbert Xu" , "Thorsten Blum" , davem@davemloft.net, nicolas.ferre@microchip.com, alexandre.belloni@bootlin.com, claudiu.beznea@tuxon.dev, "Linus Walleij" Cc: linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Message-Id: In-Reply-To: <20260422210936.20095-1-l.rubusch@gmail.com> References: <20260422210936.20095-1-l.rubusch@gmail.com> Subject: Re: [PATCH v3 0/3] crypto: atmel-sha204a - multiple RNG fixes Content-Type: text/plain Content-Transfer-Encoding: 7bit Hi Lothar, On Wed, 22 Apr 2026, at 23:09, Lothar Rubusch wrote: > When testing the RNG functionality on the Atmel SHA204a hardware, I > found the following issues: rngtest reported failures and hexdump > reveiled only the first 8 bytes out of 32 provided actually entropy. > > Having a closer look into it, I found a (small) memory leak, missing > to free work_data, miss-reading of the count field into the entropy > fields and parts of the 32 random bytes staying 0 due to reading the > slow i2c device. > > The series proposes fixes and how fixed functionality can be/was > verified. Executing rngtest afterward showed a decent result, due > to the i2c bus a bit slow. > > All setups require selecting the Atmel-sha204a as active RNG. > $ cat /sys/class/misc/hw_random/rng_available > 3f104000.rng 1-0064 none > > $ echo 1-0064 > /sys/class/misc/hw_random/rng_current > > $ cat /sys/class/misc/hw_random/rng_current > 1-0064 > > Testing RNG properties currently shows problematic results: > $ rngtest < /dev/hwrng > rngtest 2.6 > Copyright (c) 2004 by Henrique de Moraes Holschuh > This is free software; see the source for copying conditions. There is NO > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. > > rngtest: starting FIPS tests... > rngtest: bits received from input: 1040032 > rngtest: FIPS 140-2 successes: 0 > rngtest: FIPS 140-2 failures: 52 > rngtest: FIPS 140-2(2001-10-10) Monobit: 52 > rngtest: FIPS 140-2(2001-10-10) Poker: 52 > rngtest: FIPS 140-2(2001-10-10) Runs: 52 > rngtest: FIPS 140-2(2001-10-10) Long run: 52 > rngtest: FIPS 140-2(2001-10-10) Continuous run: 52 > rngtest: input channel speed: (min=7.631; avg=7.804; max=7.827)Kibits/s > rngtest: FIPS tests speed: (min=32.273; avg=32.701; max=33.056)Mibits/s > rngtest: Program run time: 130177956 microseconds > > Signed-off-by: Lothar Rubusch > --- > v2 -> v3: Removal blank line, rebased > v1 -> v2: Removal of C++ style comment (I saw it too late, sry for that) > --- > Lothar Rubusch (3): > crypto: atmel-sha204a - fix memory leak at non-blocking RNG work_data > crypto: atmel-sha204a - fix truncated 32-byte blocking read > crypto: atmel-sha204a - fix non-blocking read logic > > drivers/crypto/atmel-sha204a.c | 60 ++++++++++++++++++++++------------ > 1 file changed, 39 insertions(+), 21 deletions(-) > Thanks for the report and the fixes. However, I'm not sure you are entirely on the right track here. I managed to fix the rngtest issues that you report by making the changes below. As I already replied, I think it would be better to propose this as a standalone patch, and backport it to stable. The remaining changes are somewhat debatable IMO: the leak is not really a leak, so I'd like to understand better what you are fixing here. The command field changes seems completely misguided (unless I am missing something) --- a/drivers/crypto/atmel-sha204a.c +++ b/drivers/crypto/atmel-sha204a.c @@ -47,8 +47,8 @@ if (rng->priv) { work_data = (struct atmel_i2c_work_data *)rng->priv; - max = min(sizeof(work_data->cmd.data), max); - memcpy(data, &work_data->cmd.data, max); + max = min(RANDOM_RSP_SIZE - CMD_OVERHEAD_SIZE, max); + memcpy(data, &work_data->cmd.data[1], max); rng->priv = 0; } else { work_data = kmalloc_obj(*work_data, GFP_ATOMIC); @@ -86,8 +86,8 @@ if (ret) return ret; - max = min(sizeof(cmd.data), max); - memcpy(data, cmd.data, max); + max = min(RANDOM_RSP_SIZE - CMD_OVERHEAD_SIZE, max); + memcpy(data, &cmd.data[1], max); return max; }