[PATCH] firmware: export x86_64 platform flash bios region via sysfs

[Hans-Gert Dahmen <hans-gert.dahmen@immu.ne>]

Make the 16MiB long memory-mapped BIOS region of the platform SPI flash
on X86_64 system available via /sys/kernel/firmware/flash_mmap/bios_region
for pen-testing, security analysis and malware detection on kernels
which restrict module loading and/or access to /dev/mem.

It will be used by the open source Converged Security Suite.
https://github.com/9elements/converged-security-suite

Signed-off-by: Hans-Gert Dahmen <hans-gert.dahmen@immu.ne>
---
 drivers/firmware/Kconfig             |  9 +++
 drivers/firmware/Makefile            |  1 +
 drivers/firmware/x86_64_flash_mmap.c | 86 ++++++++++++++++++++++++++++
 3 files changed, 96 insertions(+)
 create mode 100644 drivers/firmware/x86_64_flash_mmap.c

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 75cb91055c17..27c2d0b074e0 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -293,6 +293,15 @@ config TURRIS_MOX_RWTM
 	  other manufacturing data and also utilize the Entropy Bit Generator
 	  for hardware random number generation.
 
+config X86_64_FLASH_MMAP
+	tristate "Export platform flash memory-mapped BIOS region"
+	depends on X86_64
+	help
+	  Export the memory-mapped BIOS region of the platform SPI flash as
+	  a read-only sysfs binary attribute on X86_64 systems. The first 16MiB
+	  will be accessible via /sys/devices/platform/flash_mmap/bios_region
+	  for security and malware analysis for example.
+
 source "drivers/firmware/arm_ffa/Kconfig"
 source "drivers/firmware/broadcom/Kconfig"
 source "drivers/firmware/cirrus/Kconfig"
diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index 4e58cb474a68..60dc4ea08705 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -24,6 +24,7 @@ obj-$(CONFIG_SYSFB_SIMPLEFB)	+= sysfb_simplefb.o
 obj-$(CONFIG_TI_SCI_PROTOCOL)	+= ti_sci.o
 obj-$(CONFIG_TRUSTED_FOUNDATIONS) += trusted_foundations.o
 obj-$(CONFIG_TURRIS_MOX_RWTM)	+= turris-mox-rwtm.o
+obj-$(CONFIG_X86_64_FLASH_MMAP)	+= x86_64_flash_mmap.o
 
 obj-y				+= arm_ffa/
 obj-y				+= arm_scmi/
diff --git a/drivers/firmware/x86_64_flash_mmap.c b/drivers/firmware/x86_64_flash_mmap.c
new file mode 100644
index 000000000000..23d8655d17bb
--- /dev/null
+++ b/drivers/firmware/x86_64_flash_mmap.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Export the memory-mapped BIOS region of the platform SPI flash as
+ * a read-only sysfs binary attribute on X86_64 systems.
+ *
+ * Copyright © 2021 immune GmbH
+ */
+
+#include <linux/version.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/sysfs.h>
+#include <linux/platform_device.h>
+
+#define FLASH_REGION_START 0xFF000000ULL
+#define FLASH_REGION_SIZE 0x1000000ULL
+#define FLASH_REGION_MASK (FLASH_REGION_SIZE - 1)
+
+struct platform_device *pdev;
+
+static ssize_t bios_region_read(struct file *file, struct kobject *kobj,
+				struct bin_attribute *bin_attr, char *buffer,
+				loff_t offset, size_t count)
+{
+	resource_size_t pa;
+	size_t copysize, remapsize;
+	void __iomem *va;
+
+	offset = offset & FLASH_REGION_MASK;
+	pa = (FLASH_REGION_START + offset) & PAGE_MASK;
+
+	if ((offset + count) > FLASH_REGION_SIZE)
+		copysize = FLASH_REGION_SIZE - offset;
+	else
+		copysize = min(count, PAGE_SIZE);
+
+	if (((offset & ~PAGE_MASK) + copysize) > PAGE_SIZE)
+		remapsize = 2 * PAGE_SIZE;
+	else
+		remapsize = PAGE_SIZE;
+
+	va = ioremap(pa, remapsize);
+	memcpy_fromio(buffer, va, copysize);
+	iounmap(va);
+
+	return copysize;
+}
+
+static BIN_ATTR_RO(bios_region, FLASH_REGION_SIZE);
+
+static struct bin_attribute *flash_mmap_attrs[] = { &bin_attr_bios_region,
+						    NULL };
+
+static const struct attribute_group flash_mmap_group = {
+	.bin_attrs = flash_mmap_attrs,
+};
+
+static int __init flash_mmap_init(void)
+{
+	int ret;
+
+	pdev = platform_device_register_simple("flash_mmap", -1, NULL, 0);
+	if (IS_ERR(pdev))
+		return PTR_ERR(pdev);
+
+	ret = sysfs_create_group(&pdev->dev.kobj, &flash_mmap_group);
+	if (ret) {
+		dev_err(&pdev->dev, "sysfs creation failed\n");
+		platform_device_unregister(pdev);
+	}
+
+	return ret;
+}
+
+static void __exit flash_mmap_exit(void)
+{
+	sysfs_remove_group(&pdev->dev.kobj, &flash_mmap_group);
+	platform_device_unregister(pdev);
+}
+
+module_init(flash_mmap_init);
+module_exit(flash_mmap_exit);
+MODULE_DESCRIPTION("Export SPI platform flash memory mapped region via sysfs");
+MODULE_AUTHOR("Hans-Gert Dahmen <hans-gert.dahmen@immu.ne>");
+MODULE_LICENSE("GPL");
-- 
2.32.0