linux-kernel - [PATCH] nvmem: sunxi-sid: SID content is not a valid source of randomness

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Date:   Sat, 22 Oct 2016 15:53:28 +0200
From:   Corentin Labbe <clabbe.montjoie@...il.com>
To:     srinivas.kandagatla@...aro.org, maxime.ripard@...e-electrons.com,
        wens@...e.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org,
        Corentin Labbe <clabbe.montjoie@...il.com>
Subject: [PATCH] nvmem: sunxi-sid: SID content is not a valid source of randomness

Since SID's content is constant over reboot, it must not be used
as source of randomness.

This patch remove the use of SID content as source of randomness.

Signed-off-by: Corentin Labbe <clabbe.montjoie@...il.com>
---
 drivers/nvmem/sunxi_sid.c | 21 ---------------------
 1 file changed, 21 deletions(-)

diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c
index 1567ccc..c82d5d1 100644
--- a/drivers/nvmem/sunxi_sid.c
+++ b/drivers/nvmem/sunxi_sid.c
@@ -21,8 +21,6 @@
 #include <linux/nvmem-provider.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
-#include <linux/slab.h>
-#include <linux/random.h>
 
 static struct nvmem_config econfig = {
 	.name = "sunxi-sid",
@@ -70,8 +68,6 @@ static int sunxi_sid_probe(struct platform_device *pdev)
 	struct resource *res;
 	struct nvmem_device *nvmem;
 	struct sunxi_sid *sid;
-	int ret, i, size;
-	char *randomness;
 
 	sid = devm_kzalloc(dev, sizeof(*sid), GFP_KERNEL);
 	if (!sid)
@@ -82,7 +78,6 @@ static int sunxi_sid_probe(struct platform_device *pdev)
 	if (IS_ERR(sid->base))
 		return PTR_ERR(sid->base);
 
-	size = resource_size(res) - 1;
 	econfig.size = resource_size(res);
 	econfig.dev = dev;
 	econfig.reg_read = sunxi_sid_read;
@@ -91,25 +86,9 @@ static int sunxi_sid_probe(struct platform_device *pdev)
 	if (IS_ERR(nvmem))
 		return PTR_ERR(nvmem);
 
-	randomness = kzalloc(sizeof(u8) * (size), GFP_KERNEL);
-	if (!randomness) {
-		ret = -EINVAL;
-		goto err_unreg_nvmem;
-	}
-
-	for (i = 0; i < size; i++)
-		randomness[i] = sunxi_sid_read_byte(sid, i);
-
-	add_device_randomness(randomness, size);
-	kfree(randomness);
-
 	platform_set_drvdata(pdev, nvmem);
 
 	return 0;
-
-err_unreg_nvmem:
-	nvmem_unregister(nvmem);
-	return ret;
 }
 
 static int sunxi_sid_remove(struct platform_device *pdev)
-- 
2.7.3