FAILED: patch "[PATCH] vTPM: Fix missing NULL check" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: "Hon Ching \\(Vicky\\) Lo" <[email protected]>
Date: Wed, 15 Mar 2017 01:28:07 -0400
Subject: [PATCH] vTPM: Fix missing NULL check

The current code passes the address of tpm_chip as the argument to dev_get_drvdata() without prior NULL check in tpm_ibmvtpm_get_desired_dma. This resulted an oops during kernel boot when vTPM is enabled in Power partition configured in active memory sharing mode.

The vio_driver's get_desired_dma() is called before the probe(), which for vtpm is tpm_ibmvtpm_probe, and it's this latter function that initializes the driver and set data. Attempting to get data before the probe() caused the problem.

This patch adds a NULL check to the tpm_ibmvtpm_get_desired_dma.

index 1b9d61ffe991..f01d083eced2 100644
@@ -299,6 +299,8 @@ static int tpm_ibmvtpm_remove(struct vio_dev *vdev)
 	}
 
 	kfree(ibmvtpm);
+	/* For tpm_ibmvtpm_get_desired_dma */
+	dev_set_drvdata(&vdev->dev, NULL);
 
 	return 0;
 }

@@ -313,14 +315,16 @@ static int tpm_ibmvtpm_remove(struct vio_dev *vdev)
 static unsigned long tpm_ibmvtpm_get_desired_dma(struct vio_dev *vdev)
 {
 	struct tpm_chip *chip = dev_get_drvdata(&vdev->dev);
-	struct ibmvtpm_dev *ibmvtpm = dev_get_drvdata(&chip->dev);
+	struct ibmvtpm_dev *ibmvtpm;
 
 	/*
 	 * ibmvtpm initializes at probe time, so the data we are
 	 * asking for may not be set yet. Estimate that 4K required
 	 * for TCE-mapped buffer in addition to CRQ.
 	 */
-	if (!ibmvtpm)
+	if (chip)
+		ibmvtpm = dev_get_drvdata(&chip->dev);
+	else
 		return CRQ_RES_BUF_SIZE + PAGE_SIZE;
 
 	return CRQ_RES_BUF_SIZE + ibmvtpm->rtce_size;