Re: [PATCH] tpm: Revert "tpm: fix invalid locking in NONBLOCKING mode"

[James Bottomley]

On Tue, 2020-05-26 at 13:32 -0500, Mario Limonciello wrote:
> This reverts commit d23d12484307b40eea549b8a858f5fffad913897.
> 
> This commit has caused regressions for the XPS 9560 containing
> a Nuvoton TPM.

Presumably this is using the tis driver?

> As mentioned by the reporter all TPM2 commands are failing with:
>   ERROR:tcti:src/tss2-tcti/tcti-device.c:290:tcti_device_receive()
>   Failed to read response from fd 3, got errno 1: Operation not
> permitted
> 
> The reporter bisected this issue back to this commit which was
> backported to stable as commit 4d6ebc4.

I think the problem is request_locality ... for some inexplicable
reason a failure there returns -1, which is EPERM to user space.

That seems to be a bug in the async code since everything else gives a
ESPIPE error if tpm_try_get_ops fails ... at least no-one assumes it
gives back a sensible return code.

What I think is happening is that with the patch the TPM goes through a
quick sequence of request, relinquish, request, relinquish and it's the
third request which is failing (likely timing out).  Without the patch,
the patch there's only one request,relinquish cycle because the ops are
held while the async work is executed.  I have a vague recollection
that there is a problem with too many locality request in quick
succession, but I'll defer to Jason, who I think understands the
intricacies of localities better than I do.

If that's the problem, the solution looks simple enough: just move the
ops get down because the priv state is already protected by the buffer
mutex

James

---

diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
index 87f449340202..1784530b8387 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -189,15 +189,6 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
 		goto out;
 	}
 
-	/* atomic tpm command send and result receive. We only hold the ops
-	 * lock during this period so that the tpm can be unregistered even if
-	 * the char dev is held open.
-	 */
-	if (tpm_try_get_ops(priv->chip)) {
-		ret = -EPIPE;
-		goto out;
-	}
-
 	priv->response_length = 0;
 	priv->response_read = false;
 	*off = 0;
@@ -211,11 +202,19 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
 	if (file->f_flags & O_NONBLOCK) {
 		priv->command_enqueued = true;
 		queue_work(tpm_dev_wq, &priv->async_work);
-		tpm_put_ops(priv->chip);
 		mutex_unlock(&priv->buffer_mutex);
 		return size;
 	}
 
+	/* atomic tpm command send and result receive. We only hold the ops
+	 * lock during this period so that the tpm can be unregistered even if
+	 * the char dev is held open.
+	 */
+	if (tpm_try_get_ops(priv->chip)) {
+		ret = -EPIPE;
+		goto out;
+	}
+
 	ret = tpm_dev_transmit(priv->chip, priv->space, priv->data_buffer,
 			       sizeof(priv->data_buffer));
 	tpm_put_ops(priv->chip);