[PATCH 1/4] nvmem: rockchip-otp: Serialize reads

[PATCH 1/4] nvmem: rockchip-otp: Serialize reads

[srini]

From: Alexey Charkov <alchark@flipper.net>

The OTP controller is driven through a single set of registers holding a
state machine which has to be stepped through for every word read, yet
nothing keeps two readers out of each other's way. Concurrent reads
interleave, and the outcome is either a reader bailing out:

  rockchip-otp 2a580000.otp: timeout during read setup

or, worse, one of them silently taking delivery of the other's data.

Reading two cells in parallel from userspace on RK3576 reproduces both
within 150 iterations - 53 read errors and 9 corrupted results, the latter
either losing their first word or, in one case, ending in the two bytes
which belong to the other reader's cell - whereas the same reads issued
sequentially never fail. Concurrency is not hypothetical here, as six
thermal sensors source their trim values from the OTP and reach the driver
straight from asynchronous driver probing.

Guard the read path with a mutex. Reads are the only way into the hardware,
as the driver registers no write callback, and they always run in process
context, so a plain mutex spanning the whole clock-enable, read,
clock-disable sequence is enough.

Fixes: 755864feb729 ("nvmem: add Rockchip OTP driver")
Cc: stable@vger.kernel.org
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Alexey Charkov <alchark@flipper.net>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
---
 drivers/nvmem/rockchip-otp.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/nvmem/rockchip-otp.c b/drivers/nvmem/rockchip-otp.c
index 2c0feb036f3f..f8a8c7cece98 100644
--- a/drivers/nvmem/rockchip-otp.c
+++ b/drivers/nvmem/rockchip-otp.c
@@ -12,6 +12,7 @@
 #include <linux/io.h>
 #include <linux/iopoll.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/nvmem-provider.h>
 #include <linux/reset.h>
 #include <linux/slab.h>
@@ -80,6 +81,8 @@ struct rockchip_otp {
 	void __iomem *base;
 	struct reset_control *rst;
 	const struct rockchip_data *data;
+	/* Serializes access to the OTP controller state machine */
+	struct mutex mutex;
 	struct clk_bulk_data clks[];
 };
 
@@ -272,10 +275,12 @@ static int rockchip_otp_read(void *context, unsigned int offset,
 	if (!otp->data || !otp->data->reg_read)
 		return -EINVAL;
 
+	mutex_lock(&otp->mutex);
+
 	ret = clk_bulk_prepare_enable(otp->data->num_clks, otp->clks);
 	if (ret < 0) {
 		dev_err(otp->dev, "failed to prepare/enable clks\n");
-		return ret;
+		goto unlock;
 	}
 
 	offset += otp->data->read_offset;
@@ -308,6 +313,9 @@ static int rockchip_otp_read(void *context, unsigned int offset,
 err:
 	clk_bulk_disable_unprepare(otp->data->num_clks, otp->clks);
 
+unlock:
+	mutex_unlock(&otp->mutex);
+
 	return ret;
 }
 
@@ -431,6 +439,11 @@ static int rockchip_otp_probe(struct platform_device *pdev)
 
 	otp->data = data;
 	otp->dev = dev;
+
+	ret = devm_mutex_init(dev, &otp->mutex);
+	if (ret)
+		return ret;
+
 	otp->base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(otp->base))
 		return dev_err_probe(dev, PTR_ERR(otp->base),
-- 
2.53.0

[PATCH 4/4] nvmem: core: Fix OOB read for bit offsets of more than one byte

[srini]

From: Janne Grunau <j@jannau.net>

When the bit offset is BITS_PER_BYTE or larger the read position is
advanced by `bytes_offset`. This is not taken into account in the
per-byte read loop which still reads `cell->bytes` resulting in an out of
bounds read of `bytes_offset` bytes. The information read OOB does not
leak directly as the erroneously read bits are cleared.

Detected by KASAN while looking for a use-after-free in simplefb.c.

Cc: stable@vger.kernel.org
Fixes: 7a06ef751077 ("nvmem: core: fix bit offsets of more than one byte")
Tested-by: Dmitry Sinyavin <sinyavin@gmail.com>
Signed-off-by: Janne Grunau <j@jannau.net>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
---
 drivers/nvmem/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 0556d140170a..b4e5069d9e38 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1598,12 +1598,14 @@ static void nvmem_shift_read_buffer_in_place(struct nvmem_cell_entry *cell, void
 		*p = *b++ >> bit_offset;
 
 		/* setup rest of the bytes if any */
-		for (i = 1; i < cell->bytes; i++) {
+		for (i = 1; i < (cell->bytes - bytes_offset); i++) {
 			/* Get bits from next byte and shift them towards msb */
 			*p++ |= *b << (BITS_PER_BYTE - bit_offset);
 
 			*p = *b++ >> bit_offset;
 		}
+		/* point to end of the buffer unused bits will be cleared */
+		p = buf + cell->bytes - 1;
 	} else if (p != b) {
 		memmove(p, b, cell->bytes - bytes_offset);
 		p += cell->bytes - 1;
-- 
2.53.0