[RFC][PATCH 1/2] Add a layer of abstraction to use the memory reserved by device tree for ima buffer pass.

[Prakhar Srivastava <prsriva@linux.microsoft.com>]

Introduce a device tree layer for to read and store ima buffer
from the reserved memory section of a device tree.

Signed-off-by: Prakhar Srivastava <prsriva@linux.microsoft.com>
---
 drivers/of/Kconfig  |   6 ++
 drivers/of/Makefile |   1 +
 drivers/of/of_ima.c | 165 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/of.h  |  34 +++++++++
 4 files changed, 206 insertions(+)
 create mode 100644 drivers/of/of_ima.c

diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index d91618641be6..edb3c39740fb 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -107,4 +107,10 @@ config OF_DMA_DEFAULT_COHERENT
 	# arches should select this if DMA is coherent by default for OF devices
 	bool
 
+config OF_IMA
+	def_bool y
+	help
+	  IMA related wrapper functions to add/remove ima measurement logs during
+	  kexec_file_load call.
+
 endif # OF
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index 663a4af0cccd..b4caf083df4e 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -14,5 +14,6 @@ obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
 obj-$(CONFIG_OF_RESOLVE)  += resolver.o
 obj-$(CONFIG_OF_OVERLAY) += overlay.o
 obj-$(CONFIG_OF_NUMA) += of_numa.o
+obj-$(CONFIG_OF_IMA) += of_ima.o
 
 obj-$(CONFIG_OF_UNITTEST) += unittest-data/
diff --git a/drivers/of/of_ima.c b/drivers/of/of_ima.c
new file mode 100644
index 000000000000..131f68d81e2e
--- /dev/null
+++ b/drivers/of/of_ima.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Microsoft Corporation.
+ */
+
+#include <linux/slab.h>
+#include <linux/kexec.h>
+#include <linux/of.h>
+#include <linux/memblock.h>
+#include <linux/libfdt.h>
+#include <linux/of_address.h>
+
+static bool dtb_status_enabled;
+static struct resource mem_res;
+static void *vaddr;
+
+
+/**
+ * of_is_ima_memory_reserved - check if memory is reserved via device
+ *							tree.
+ *	Return: zero when memory is not reserved.
+ *			positive number on success.
+ *
+ */
+int of_is_ima_memory_reserved(void)
+{
+	return dtb_status_enabled;
+}
+
+/**
+ * of_ima_write_buffer - Write the ima buffer into the reserved memory.
+ *
+ * ima_buffer - buffer starting address.
+ * ima_buffer_size - size of segment.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int of_ima_write_buffer(void *ima_buffer, size_t ima_buffer_size)
+{
+	void *addr;
+
+	if (!dtb_status_enabled)
+		return -EOPNOTSUPP;
+
+	vaddr = memremap(mem_res.start, resource_size(&mem_res), MEMREMAP_WB);
+	pr_info("Mapped reserved memory, vaddr: 0x%0llX, paddr: 0x%0llX\n , size : %lld",
+	(u64)vaddr, mem_res.start, resource_size(&mem_res));
+
+	if (vaddr) {
+		memcpy(vaddr, &ima_buffer_size, sizeof(size_t));
+		addr =  vaddr + sizeof(size_t);
+		memcpy(addr, ima_buffer, ima_buffer_size);
+		memunmap(vaddr);
+		vaddr = NULL;
+	}
+
+	return 0;
+}
+
+/**
+ * of_remove_ima_buffer - Write 0(Zero length buffer to read)to the
+ *                        size location of the buffer.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int of_remove_ima_buffer(void)
+{
+	size_t empty_buffer_size = 0;
+
+	if (!dtb_status_enabled)
+		return -ENOTSUPP;
+
+	if (vaddr) {
+		memcpy(vaddr, &empty_buffer_size, sizeof(size_t));
+		memunmap(vaddr);
+		vaddr = NULL;
+	}
+
+	return 0;
+}
+
+/**
+ * of_ima_get_size_allocated - Get the usable buffer size thats allocated in
+ *                             the device-tree.
+ *
+ * Return: 0 on unavailable node, size of the memory block - (size_t)
+ */
+size_t of_ima_get_size_allocated(void)
+{
+	size_t size = 0;
+
+	if (!dtb_status_enabled)
+		return size;
+
+	size = resource_size(&mem_res) - sizeof(size_t);
+	return size;
+}
+
+/**
+ * of_get_ima_buffer - Get IMA buffer address.
+ *
+ * @addr:       On successful return, set to point to the buffer contents.
+ * @size:       On successful return, set to the buffer size.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int of_get_ima_buffer(void **addr, size_t *size)
+{
+	if (!dtb_status_enabled)
+		return -ENOTSUPP;
+
+	vaddr = memremap(mem_res.start, resource_size(&mem_res), MEMREMAP_WB);
+	pr_info("Mapped reserved memory, vaddr: 0x%0llX, paddr: 0x%0llX,\n allocated size : %lld, ima_buffer_size: %ld ",
+	(u64)vaddr, mem_res.start, resource_size(&mem_res), *(size_t *)vaddr);
+
+	*size = *(size_t *)vaddr;
+	*addr = vaddr + sizeof(size_t);
+	return 0;
+}
+
+static const struct of_device_id ima_buffer_pass_ids[] = {
+	{
+		.compatible = "linux,ima_buffer_pass",
+	},
+	{}
+};
+
+static const struct of_device_id ima_buffer_pass_match[] = {
+	{
+		.name = "ima_buffer_pass",
+	},
+};
+MODULE_DEVICE_TABLE(of, ima_buffer_pass_match);
+
+static int __init ima_buffer_pass_init(void)
+{
+	int ret = 0;
+	struct device_node *memnp;
+	struct device_node *ima_buffer_pass_node;
+
+	ima_buffer_pass_node = of_find_matching_node(NULL, ima_buffer_pass_ids);
+	if (!ima_buffer_pass_node)
+		return -ENOENT;
+
+	memnp = of_parse_phandle(ima_buffer_pass_node, "memory-region", 0);
+	if (!memnp)
+		return -ENXIO;
+
+	ret = of_address_to_resource(memnp, 0, &mem_res);
+	if (ret < 0)
+		return -ENOENT;
+
+	of_node_put(memnp);
+	dtb_status_enabled = true;
+
+	return ret;
+}
+
+static void __exit ima_buffer_pass_exit(void)
+{
+	pr_info("trying to exit the ima driver\n");
+}
+
+module_init(ima_buffer_pass_init);
+module_exit(ima_buffer_pass_exit);
diff --git a/include/linux/of.h b/include/linux/of.h
index c669c0a4732f..85ce2f24024f 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -1485,4 +1485,38 @@ static inline int of_overlay_notifier_unregister(struct notifier_block *nb)
 
 #endif
 
+#ifdef CONFIG_OF_IMA
+int of_is_ima_memory_reserved(void);
+int of_remove_ima_buffer(void);
+int of_get_ima_buffer(void **addr, size_t *size);
+size_t of_ima_get_size_allocated(void);
+int of_ima_write_buffer(void *ima_buffer,
+		size_t ima_buffer_size);
+#else
+static inline int of_is_ima_memory_reserved(void)
+{
+	return -ENOTSUPP;
+};
+static inline int of_remove_ima_buffer(void)
+{
+	return -ENOTSUPP;
+};
+
+static inline int of_get_ima_buffer(void **addr, size_t *size)
+{
+	return -ENOTSUPP;
+};
+
+static inline size_t of_ima_get_size_allocated(void)
+{
+	return 0;
+};
+
+static inline int of_ima_write_buffer(void *ima_buffer,
+				      size_t ima_buffer_size)
+{
+	return -ENOTSUPP;
+};
+#endif
+
 #endif /* _LINUX_OF_H */
-- 
2.25.1