Re: [PATCH 3/4] drivers/misc: Add ASpeed LPC control driver

On Thu, Jan 12, 2017 at 09:16:03PM +1100, Cyril Bur wrote:

On Thu, 2017-01-12 at 08:47 +0100, Greg KH wrote:

quoted

On Thu, Jan 12, 2017 at 11:29:09AM +1100, Cyril Bur wrote:

quoted

+static ssize_t lpc_ctrl_read(struct file *file, char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	if (!access_ok(VERIFY_WRITE, buf, count))
+		return -EFAULT;
+
+	return -EPERM;
+}
+
+static ssize_t lpc_ctrl_write(struct file *file, const char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	if (!access_ok(VERIFY_READ, buf, count))
+		return -EFAULT;
+
+	return -EPERM;
+}

Hello Greg,

quoted

Those functions don't actually do anything, so why even include them?

Apologies, I should be more careful with what I send.

Hm, that implies you never tested what you sent, nor intended for us to
merge it, an odd thing for you to do :)

quoted

And don't call access_ok(), it's racy and no driver should ever do that.

Oh, duly noted. I'll be sure to check out how and why. Perhaps it
would be wise that no driver actually do that, I'm quite sure I used
other drivers as examples of best practice.

You did?  Please point me at that code so we can fix them up properly.
Cargo-cult coding is not a good thing, but it happens, so if we can at
least provide clean code to fixate on, it's good overall for everyone.

quoted

quoted

+static long lpc_ctrl_ioctl(struct file *file, unsigned int cmd,
+		unsigned long param)
+{
+	long rc;
+	struct lpc_mapping map;
+	struct lpc_ctrl *lpc_ctrl = file_lpc_ctrl(file);
+	void __user *p = (void __user *)param;
+
+	switch (cmd) {
+	case LPC_CTRL_IOCTL_SIZE:
+		return copy_to_user(p, &lpc_ctrl->size,
+			sizeof(lpc_ctrl->size)) ? -EFAULT : 0;
+	case LPC_CTRL_IOCTL_MAP:
+		if (copy_from_user(&map, p, sizeof(map)))
+			return -EFAULT;
+
+
+		/*
+		 * The top half of HICR7 is the MSB of the BMC address of the
+		 * mapping.
+		 * The bottom half of HICR7 is the MSB of the HOST LPC
+		 * firmware space address of the mapping.
+		 *
+		 * The 1 bits in the top of half of HICR8 represent the bits
+		 * (in the requested address) that should be ignored and
+		 * replaced with those from the top half of HICR7.
+		 * The 1 bits in the bottom half of HICR8 represent the bits
+		 * (in the requested address) that should be kept and pass
+		 * into the BMC address space.
+		 */
+
+		rc = regmap_write(lpc_ctrl->regmap, HICR7,
+				(lpc_ctrl->base | (map.hostaddr >> 16)));
+		if (rc)
+			return rc;
+
+		rc = regmap_write(lpc_ctrl->regmap, HICR8,
+			(~(map.size - 1)) | ((map.size >> 16) - 1));

Look Ma, a kernel exploit!

So 'evil' input here could allow the host to control the bmc,
personally I file that under 'stupid' input. Also, stupid but not
accidental, I don't believe one could accidentally come up with such
input, although you never know what silly things human beings sometimes
do. For what its worth, I'm not even sure that can happen but I'll
grant you the benifit of the doubt.

I think you didn't get the main point here, again:

quoted

{sigh}

Your assignment is to go find a whiteboard/blackboard/whatever and write
on it 100 times:
	All input is evil.

You can NEVER trust any input values sent to the kernel, you have to
ALWAYS verify they are within certain safe ranges.

quoted

I want to see the picture of that before you send any more kernel patches.

quoted

+static int lpc_ctrl_release(struct inode *inode, struct file *file)
+{
+	atomic_dec(&lpc_ctrl_open_count);

Totally unneeded and unnecessary, why do you care?

My aim here was to only have one process playing with the LPC mapping
registers at a time.

Why?  Who cares?  You don't have internal state being kept by the
driver, so it shouldn't matter.

And again, don't treat an atomic variable as a lock, use a real lock for
the task, it works better, and is the correct thing to do.

thanks,

greg k-h
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