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, 77 insertions, 0 deletions

diff --git a/drivers/nvmem/uniphier-efuse.c b/drivers/nvmem/uniphier-efuse.c
new file mode 100644
index 000000000..85f9372fb
--- /dev/null
+++ b/drivers/nvmem/uniphier-efuse.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * UniPhier eFuse driver
+ *
+ * Copyright (C) 2017 Socionext Inc.
+ */
+
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+
+struct uniphier_efuse_priv {
+	void __iomem *base;
+};
+
+static int uniphier_reg_read(void *context,
+			     unsigned int reg, void *_val, size_t bytes)
+{
+	struct uniphier_efuse_priv *priv = context;
+	u8 *val = _val;
+	int offs;
+
+	for (offs = 0; offs < bytes; offs += sizeof(u8))
+		*val++ = readb(priv->base + reg + offs);
+
+	return 0;
+}
+
+static int uniphier_efuse_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct resource *res;
+	struct nvmem_device *nvmem;
+	struct nvmem_config econfig = {};
+	struct uniphier_efuse_priv *priv;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	econfig.stride = 1;
+	econfig.word_size = 1;
+	econfig.read_only = true;
+	econfig.reg_read = uniphier_reg_read;
+	econfig.size = resource_size(res);
+	econfig.priv = priv;
+	econfig.dev = dev;
+	econfig.add_legacy_fixed_of_cells = true;
+	nvmem = devm_nvmem_register(dev, &econfig);
+
+	return PTR_ERR_OR_ZERO(nvmem);
+}
+
+static const struct of_device_id uniphier_efuse_of_match[] = {
+	{ .compatible = "socionext,uniphier-efuse",},
+	{/* sentinel */},
+};
+MODULE_DEVICE_TABLE(of, uniphier_efuse_of_match);
+
+static struct platform_driver uniphier_efuse_driver = {
+	.probe = uniphier_efuse_probe,
+	.driver = {
+		.name = "uniphier-efuse",
+		.of_match_table = uniphier_efuse_of_match,
+	},
+};
+module_platform_driver(uniphier_efuse_driver);
+
+MODULE_AUTHOR("Keiji Hayashibara <hayashibara.keiji@socionext.com>");
+MODULE_DESCRIPTION("UniPhier eFuse driver");
+MODULE_LICENSE("GPL v2");