[PATCH v7 4/5] efi: Load efi_secret module if EFI secret area is populated

[Dov Murik]

If the efi_secret module is built, register a late_initcall in the EFI
driver which checks whether the EFI secret area is available and
populated, and then requests to load the efi_secret module.

This will cause the <securityfs>/coco/efi_secret directory to appear in
guests into which secrets were injected; in other cases, the module is
not loaded.

Signed-off-by: Dov Murik <dovmurik@xxxxxxxxxxxxx>
---
 drivers/firmware/efi/Makefile        |  1 +
 drivers/firmware/efi/coco.c          | 58 ++++++++++++++++++++++++++++
 drivers/virt/coco/efi_secret/Kconfig |  3 ++
 3 files changed, 62 insertions(+)
 create mode 100644 drivers/firmware/efi/coco.c

diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index c02ff25dd477..49c4a8c0bfc4 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_APPLE_PROPERTIES)		+= apple-properties.o
 obj-$(CONFIG_EFI_RCI2_TABLE)		+= rci2-table.o
 obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE)	+= embedded-firmware.o
 obj-$(CONFIG_LOAD_UEFI_KEYS)		+= mokvar-table.o
+obj-$(CONFIG_EFI_COCO_SECRET)		+= coco.o
 
 fake_map-y				+= fake_mem.o
 fake_map-$(CONFIG_X86)			+= x86_fake_mem.o
diff --git a/drivers/firmware/efi/coco.c b/drivers/firmware/efi/coco.c
new file mode 100644
index 000000000000..f8efd240ab05
--- /dev/null
+++ b/drivers/firmware/efi/coco.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Confidential computing (coco) secret area handling
+ *
+ * Copyright (C) 2021 IBM Corporation
+ * Author: Dov Murik <dovmurik@xxxxxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/efi.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kmod.h>
+
+#ifdef CONFIG_EFI_SECRET_MODULE
+
+/*
+ * Load the efi_secret module if the EFI secret area is populated
+ */
+static int __init load_efi_secret_module(void)
+{
+	struct linux_efi_coco_secret_area *area;
+	efi_guid_t *header_guid;
+	int ret = 0;
+
+	if (efi.coco_secret == EFI_INVALID_TABLE_ADDR)
+		return 0;
+
+	area = memremap(efi.coco_secret, sizeof(*area), MEMREMAP_WB);
+	if (!area) {
+		pr_err("Failed to map confidential computing secret area descriptor\n");
+		return -ENOMEM;
+	}
+	if (!area->base_pa || area->size < sizeof(*header_guid))
+		goto unmap_desc;
+
+	header_guid = (void __force *)ioremap_encrypted(area->base_pa, sizeof(*header_guid));
+	if (!header_guid) {
+		pr_err("Failed to map secret area\n");
+		ret = -ENOMEM;
+		goto unmap_desc;
+	}
+	if (efi_guidcmp(*header_guid, EFI_SECRET_TABLE_HEADER_GUID))
+		goto unmap_encrypted;
+
+	ret = request_module("efi_secret");
+
+unmap_encrypted:
+	iounmap((void __iomem *)header_guid);
+
+unmap_desc:
+	memunmap(area);
+	return ret;
+}
+late_initcall(load_efi_secret_module);
+
+#endif
diff --git a/drivers/virt/coco/efi_secret/Kconfig b/drivers/virt/coco/efi_secret/Kconfig
index ed181797ed86..068fdd1fccd7 100644
--- a/drivers/virt/coco/efi_secret/Kconfig
+++ b/drivers/virt/coco/efi_secret/Kconfig
@@ -14,3 +14,6 @@ config EFI_SECRET
 
 	  To compile this driver as a module, choose M here.
 	  The module will be called efi_secret.
+
+	  The module is loaded automatically by the EFI driver if the EFI
+	  secret area is populated.
-- 
2.25.1