tpm20: Move user copies outside the lifecycle lock

The TPM 2.0 character-device methods held the global device lock
while uiomove() accessed user memory.  User page faults could therefore
delay suspend or detach even though the read response was already
buffered.

Add a per-open sleepable lock to serialize operations on each response
buffer.  Stage commands under that lock before acquiring the device
lock, and copy them into the response buffer only after the lifecycle
checks succeed.  This preserves an unread response when suspend or
detach rejects a write.  Release the device lock before copying buffered
responses out.  Also advance the response offset by the bytes actually
copied when uiomove() returns after a partial transfer.

Validated on an Intel TPM 2.0 TIS device.  PCR reads and GetRandom
passed under 16-process mixed command load.  A response was consumed
correctly in 5-byte, 7-byte, and remainder reads.  Module unload/reload
recreated the device and entropy source without lock diagnostics.
Source inspection confirmed rejected writes preserve unread responses.

Reviewed by:	kevans
MFC after:	2 weeks
Sponsored by:	BBOX.io
Differential Revision:	https://reviews.freebsd.org/D59245

2 files changed, 30 insertions, 8 deletions

diff --git a/sys/dev/tpm/tpm20.c b/sys/dev/tpm/tpm20.c
index bebf0af400fa..6c96f1ce848d 100644
--- a/sys/dev/tpm/tpm20.c
+++ b/sys/dev/tpm/tpm20.c
@@ -86,6 +86,7 @@ tpm20_read(struct cdev *dev, struct uio *uio, int flags)
 	struct tpm_priv *priv;
 	size_t bytes_to_transfer;
 	size_t offset;
+	ssize_t resid;
 	int result;
 
 	sc = (struct tpm_sc *)dev->si_drv1;
@@ -93,27 +94,36 @@ tpm20_read(struct cdev *dev, struct uio *uio, int flags)
 	if (result != 0)
 		return (result);
 
+	sx_xlock(&priv->io_lock);
 	sx_xlock(&sc->dev_lock);
 	if (atomic_load_bool(&sc->dying)) {
 		result = ENXIO;
-		goto out;
+		goto out_locked;
 	}
 	if (sc->suspended) {
 		result = EBUSY;
-		goto out;
+		goto out_locked;
 	}
 	offset = priv->offset;
 	bytes_to_transfer = MIN(priv->len, uio->uio_resid);
+	sx_xunlock(&sc->dev_lock);
+
 	if (bytes_to_transfer > 0) {
-		result = uiomove((caddr_t) priv->buf + offset, bytes_to_transfer, uio);
+		resid = uio->uio_resid;
+		result = uiomove((caddr_t)priv->buf + offset,
+		    (int)bytes_to_transfer, uio);
+		bytes_to_transfer = resid - uio->uio_resid;
 		priv->offset += bytes_to_transfer;
 		priv->len -= bytes_to_transfer;
 	} else {
 		result = 0;
 	}
+	sx_xunlock(&priv->io_lock);
+	return (result);
 
-out:
+out_locked:
 	sx_xunlock(&sc->dev_lock);
+	sx_xunlock(&priv->io_lock);
 	return (result);
 }
 
@@ -122,6 +132,7 @@ tpm20_write(struct cdev *dev, struct uio *uio, int flags)
 {
 	struct tpm_sc *sc;
 	struct tpm_priv *priv;
+	uint8_t *command;
 	size_t byte_count;
 	int result;
 
@@ -143,6 +154,12 @@ tpm20_write(struct cdev *dev, struct uio *uio, int flags)
 		return (E2BIG);
 	}
 
+	command = malloc(byte_count, M_TPM20, M_WAITOK);
+	sx_xlock(&priv->io_lock);
+	result = uiomove(command, byte_count, uio);
+	if (result != 0)
+		goto out_priv;
+
 	sx_xlock(&sc->dev_lock);
 	if (atomic_load_bool(&sc->dying)) {
 		result = ENXIO;
@@ -153,14 +170,16 @@ tpm20_write(struct cdev *dev, struct uio *uio, int flags)
 		goto out;
 	}
 
-	result = uiomove(priv->buf, byte_count, uio);
-	if (result != 0)
-		goto out;
-
+	memcpy(priv->buf, command, byte_count);
 	result = TPM_TRANSMIT(sc->dev, priv, byte_count);
 
 out:
 	sx_xunlock(&sc->dev_lock);
+	if (result != 0)
+		uio->uio_resid = byte_count;
+out_priv:
+	sx_xunlock(&priv->io_lock);
+	free(command, M_TPM20);
 	return (result);
 }
 
@@ -170,6 +189,7 @@ tpm20_priv_alloc(void)
 	struct tpm_priv *priv;
 
 	priv = malloc(sizeof (*priv), M_TPM20, M_WAITOK | M_ZERO);
+	sx_init(&priv->io_lock, "TPM per-open I/O lock");
 	return (priv);
 }
 
@@ -178,6 +198,7 @@ tpm20_priv_dtor(void *data)
 {
 	struct tpm_priv *priv = data;
 
+	sx_destroy(&priv->io_lock);
 	free(priv, M_TPM20);
 }
 
diff --git a/sys/dev/tpm/tpm20.h b/sys/dev/tpm/tpm20.h
index 1d7a11265b02..f210cd84c331 100644
--- a/sys/dev/tpm/tpm20.h
+++ b/sys/dev/tpm/tpm20.h
@@ -110,6 +110,7 @@
 MALLOC_DECLARE(M_TPM20);
 
 struct tpm_priv {
+	struct sx	io_lock;
 	uint8_t 	buf[TPM_BUFSIZE];
 	size_t		offset;
 	size_t		len;