linux-kernel - [PATCH 2/2] hwrng: stm32 - fix read of the last word

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Date:   Wed, 12 Oct 2022 18:09:24 +0200
From:   Tomas Marek <tomas.marek@...est.cz>
To:     mpm@...enic.com, herbert@...dor.apana.org.au
Cc:     mcoquelin.stm32@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        alexandre.torgue@...s.st.com, oleg.karfich@...o.com,
        Tomas Marek <tomas.marek@...est.cz>
Subject: [PATCH 2/2] hwrng: stm32 - fix read of the last word

The stm32_rng_read() function samples TRNG by 4 bytes until at
least 5 bytes are free in the input buffer. The last four bytes
are never read. For example, 60 bytes are returned in case the
input buffer size is 64 bytes.

Read until at least 4 bytes are free in the input buffer. Fill
the buffer entirely in case the buffer size is divisible by 4.

Cc: Oleg Karfich <oleg.karfich@...o.com>
Signed-off-by: Tomas Marek <tomas.marek@...est.cz>
---
 drivers/char/hw_random/stm32-rng.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
index 8eaacefd498b..366edda4848b 100644
--- a/drivers/char/hw_random/stm32-rng.c
+++ b/drivers/char/hw_random/stm32-rng.c
@@ -44,7 +44,7 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 
 	pm_runtime_get_sync((struct device *) priv->rng.priv);
 
-	while (max > sizeof(u32)) {
+	while (max >= sizeof(u32)) {
 		sr = readl_relaxed(priv->base + RNG_SR);
 		/* Manage timeout which is based on timer and take */
 		/* care of initial delay time when enabling rng	*/
-- 
2.17.1