openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 54 insertions, 0 deletions

diff --git a/drivers/char/tpm/tpmrm-dev.c b/drivers/char/tpm/tpmrm-dev.c
new file mode 100644
index 000000000..19e8f2779
--- /dev/null
+++ b/drivers/char/tpm/tpmrm-dev.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2017 James.Bottomley@HansenPartnership.com
+ */
+#include <linux/slab.h>
+#include "tpm-dev.h"
+
+struct tpmrm_priv {
+	struct file_priv priv;
+	struct tpm_space space;
+};
+
+static int tpmrm_open(struct inode *inode, struct file *file)
+{
+	struct tpm_chip *chip;
+	struct tpmrm_priv *priv;
+	int rc;
+
+	chip = container_of(inode->i_cdev, struct tpm_chip, cdevs);
+	priv = kzalloc_obj(*priv);
+	if (priv == NULL)
+		return -ENOMEM;
+
+	rc = tpm2_init_space(&priv->space, TPM2_SPACE_BUFFER_SIZE);
+	if (rc) {
+		kfree(priv);
+		return -ENOMEM;
+	}
+
+	tpm_common_open(file, chip, &priv->priv, &priv->space);
+
+	return nonseekable_open(inode, file);
+}
+
+static int tpmrm_release(struct inode *inode, struct file *file)
+{
+	struct file_priv *fpriv = file->private_data;
+	struct tpmrm_priv *priv = container_of(fpriv, struct tpmrm_priv, priv);
+
+	tpm_common_release(file, fpriv);
+	tpm2_del_space(fpriv->chip, &priv->space);
+	kfree(priv);
+
+	return 0;
+}
+
+const struct file_operations tpmrm_fops = {
+	.owner = THIS_MODULE,
+	.open = tpmrm_open,
+	.read = tpm_common_read,
+	.write = tpm_common_write,
+	.poll = tpm_common_poll,
+	.release = tpmrm_release,
+};