[PATCH v8 3/4] efi: Load efi_secret module if EFI secret area is populated

Dov Murik
2022-02-28T11:43:38Z

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>/secrets/coco directory to appear in
guests into which secrets were injected; in other cases, the module is
not loaded.

Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
---
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/coco.c | 58 ++++++++++++++++++++
drivers/virt/coco/efi_secret/Kconfig | 3 +
3 files changed, 62 insertions(+)

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@linux.ibm.com>
+ */
+
+#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 4404d198f3b2..dc8da2921e36 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