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