[PATCH v2 4/4] crypto: exynos - Introduce mutex to prevent concurrent access to hardware

[Łukasz Stelmach]

Cc: Marek Szyprowski <m.szyprow...@samsung.com>, Bartlomiej Zolnierkiewicz 
<b.zolnier...@samsung.com>

Hardware operations like reading random numbers and setting a seed need
to be conducted in a single thread. Therefore a mutex is required to
prevent multiple threads (processes) from accessing the hardware at the
same time.

The sequence of mutex_lock() and mutex_unlock() in the exynos_rng_reseed()
function enables switching between different threads waiting for the
driver to generate random numbers for them.

Signed-off-by: Łukasz Stelmach <l.stelm...@samsung.com>
---
 drivers/crypto/exynos-rng.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/crypto/exynos-rng.c b/drivers/crypto/exynos-rng.c
index c72a838f1932..6209035ca659 100644
--- a/drivers/crypto/exynos-rng.c
+++ b/drivers/crypto/exynos-rng.c
@@ -22,6 +22,7 @@
 #include <linux/err.h>
 #include <linux/io.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 
@@ -79,6 +80,7 @@ struct exynos_rng_dev {
        enum exynos_prng_type           type;
        void __iomem                    *mem;
        struct clk                      *clk;
+       struct mutex                    lock;
        /* Generated numbers stored for seeding during resume */
        u8                              seed_save[EXYNOS_RNG_SEED_SIZE];
        unsigned int                    seed_save_len;
@@ -192,6 +194,10 @@ static void exynos_rng_reseed(struct exynos_rng_dev *rng)
                return;
 
        exynos_rng_set_seed(rng, seed, read);
+
+       /* Let others do some of their job. */
+       mutex_unlock(&rng->lock);
+       mutex_lock(&rng->lock);
 }
 
 static int exynos_rng_generate(struct crypto_rng *tfm,
@@ -207,6 +213,7 @@ static int exynos_rng_generate(struct crypto_rng *tfm,
        if (ret)
                return ret;
 
+       mutex_lock(&rng->lock);
        do {
                ret = exynos_rng_get_random(rng, dst, dlen, &read);
                if (ret)
@@ -217,6 +224,7 @@ static int exynos_rng_generate(struct crypto_rng *tfm,
 
                exynos_rng_reseed(rng);
        } while (dlen > 0);
+       mutex_unlock(&rng->lock);
 
        clk_disable_unprepare(rng->clk);
 
@@ -234,7 +242,9 @@ static int exynos_rng_seed(struct crypto_rng *tfm, const u8 
*seed,
        if (ret)
                return ret;
 
+       mutex_lock(&rng->lock);
        ret = exynos_rng_set_seed(ctx->rng, seed, slen);
+       mutex_unlock(&rng->lock);
 
        clk_disable_unprepare(rng->clk);
 
@@ -284,6 +294,8 @@ static int exynos_rng_probe(struct platform_device *pdev)
                return -ENOTSUPP;
        }
 
+       mutex_init(&rng->lock);
+
        rng->dev = &pdev->dev;
        rng->clk = devm_clk_get(&pdev->dev, "secss");
        if (IS_ERR(rng->clk)) {
@@ -334,9 +346,14 @@ static int __maybe_unused exynos_rng_suspend(struct device 
*dev)
        if (ret)
                return ret;
 
+       mutex_lock(&rng->lock);
+
        /* Get new random numbers and store them for seeding on resume. */
        exynos_rng_get_random(rng, rng->seed_save, sizeof(rng->seed_save),
                              &(rng->seed_save_len));
+
+       mutex_unlock(&rng->lock);
+
        dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
                rng->seed_save_len);
 
@@ -359,8 +376,12 @@ static int __maybe_unused exynos_rng_resume(struct device 
*dev)
        if (ret)
                return ret;
 
+       mutex_lock(&rng->lock);
+
        ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);
 
+       mutex_unlock(&rng->lock);
+
        clk_disable_unprepare(rng->clk);
 
        return ret;
-- 
2.11.0