Confidential computing (coco) hardware such as AMD SEV (Secure Encrypted
Virtualization) allows guest owners to inject secrets into the VMs
memory without the host/hypervisor being able to read them. In SEV,
secret injection is performed early in the VM launch process, before the
guest starts running.
OVMF already reserves designated area for secret injection (in its
AmdSev package; see edk2 commit 01726b6d23d4 "OvmfPkg/AmdSev: Expose the
Sev Secret area using a configuration table" [1]), but the secrets were
not available in the guest kernel.
The patch series copies the secrets from the EFI-provided memory to
kernel reserved memory, and optionally exposes them to userspace via
securityfs using a new efi_secret kernel module.
The first patch in efi/libstub copies the secret area from the EFI
memory to specially allocated memory; the second patch reserves that
memory block; and the third patch introduces the new efi_secret module
that exposes the content of the secret entries as securityfs files, and
allows clearing out secrets with a file unlink interface.
As a usage example, consider a guest performing computations on
encrypted files. The Guest Owner provides the decryption key (= secret)
using the secret injection mechanism. The guest application reads the
secret from the efi_secret filesystem and proceeds to decrypt the files
into memory and then performs the needed computations on the content.
In this example, the host can't read the files from the disk image
because they are encrypted. Host can't read the decryption key because
it is passed using the secret injection mechanism (= secure channel).
Host can't read the decrypted content from memory because it's a
confidential (memory-encrypted) guest.
This has been tested with AMD SEV and SEV-ES guests, but the kernel side
of handling the secret area has no SEV-specific dependencies, and
therefore might be usable (perhaps with minor changes) for any
confidential computing hardware that can publish the secret area via the
standard EFI config table entry.
Here is a simple example for usage of the efi_secret module in a guest
to which an EFI secret area with 4 secrets was injected during launch:
# modprobe efi_secret
# ls -la /sys/kernel/security/coco/efi_secret
total 0
drwxr-xr-x 2 root root 0 Jun 28 11:54 .
drwxr-xr-x 3 root root 0 Jun 28 11:54 ..
-r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
-r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
-r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
-r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910
# xxd /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910
00000000: 7468 6573 652d 6172 652d 7468 652d 6b61 these-are-the-ka
00000010: 7461 2d73 6563 7265 7473 0001 0203 0405 ta-secrets......
00000020: 0607 ..
# rm /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910
# ls -la /sys/kernel/security/coco/efi_secret
total 0
drwxr-xr-x 2 root root 0 Jun 28 11:55 .
drwxr-xr-x 3 root root 0 Jun 28 11:54 ..
-r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
-r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
-r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
[1] https://github.com/tianocore/edk2/commit/01726b6d23d4
---
v3 changes:
- Rename the module to efi_secret
- Remove the exporting of clean_cache_range
- Use clflush_cache_range in wipe_memory
- Document function wipe_memory
- Initialize efi.coco_secret to EFI_INVALID_TABLE_ADDR to correctly detect
when there's no secret area published in the EFI configuration tables
v2: https://lore.kernel.org/linux-coco/[email protected]
v2 changes:
- Export clean_cache_range()
- When deleteing a secret, call clean_cache_range() after explicit_memzero
- Add Documentation/ABI/testing/securityfs-coco-sev_secret
v1: https://lore.kernel.org/linux-coco/[email protected]/
RFC: https://lore.kernel.org/linux-coco/[email protected]/
Dov Murik (3):
efi/libstub: Copy confidential computing secret area
efi: Reserve confidential computing secret area
virt: Add efi_secret module to expose confidential computing secrets
.../ABI/testing/securityfs-coco-efi_secret | 50 +++
arch/x86/platform/efi/efi.c | 1 +
drivers/firmware/efi/Makefile | 2 +-
drivers/firmware/efi/coco.c | 41 +++
drivers/firmware/efi/efi.c | 4 +
drivers/firmware/efi/libstub/Makefile | 2 +-
drivers/firmware/efi/libstub/coco.c | 68 ++++
drivers/firmware/efi/libstub/efi-stub.c | 2 +
drivers/firmware/efi/libstub/efistub.h | 2 +
drivers/firmware/efi/libstub/x86-stub.c | 2 +
drivers/virt/Kconfig | 3 +
drivers/virt/Makefile | 1 +
drivers/virt/coco/efi_secret/Kconfig | 10 +
drivers/virt/coco/efi_secret/Makefile | 2 +
drivers/virt/coco/efi_secret/efi_secret.c | 324 ++++++++++++++++++
include/linux/efi.h | 9 +
16 files changed, 521 insertions(+), 2 deletions(-)
create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret
create mode 100644 drivers/firmware/efi/coco.c
create mode 100644 drivers/firmware/efi/libstub/coco.c
create mode 100644 drivers/virt/coco/efi_secret/Kconfig
create mode 100644 drivers/virt/coco/efi_secret/Makefile
create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c
base-commit: 60a9483534ed0d99090a2ee1d4bb0b8179195f51
--
2.25.1
When efi-stub copies an EFI-provided confidential computing (coco)
secret area, reserve that memory block for future use within the kernel.
Signed-off-by: Dov Murik <[email protected]>
---
arch/x86/platform/efi/efi.c | 1 +
drivers/firmware/efi/Makefile | 2 +-
drivers/firmware/efi/coco.c | 41 +++++++++++++++++++++++++++++++++++
drivers/firmware/efi/efi.c | 4 ++++
include/linux/efi.h | 3 +++
5 files changed, 50 insertions(+), 1 deletion(-)
create mode 100644 drivers/firmware/efi/coco.c
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 147c30a81f15..35e082e5f603 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -93,6 +93,7 @@ static const unsigned long * const efi_tables[] = {
#ifdef CONFIG_LOAD_UEFI_KEYS
&efi.mokvar_table,
#endif
+ &efi.coco_secret,
};
u64 efi_setup; /* efi setup_data physical address */
diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index c02ff25dd477..bfd35294703e 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -12,7 +12,7 @@ KASAN_SANITIZE_runtime-wrappers.o := n
obj-$(CONFIG_ACPI_BGRT) += efi-bgrt.o
obj-$(CONFIG_EFI) += efi.o vars.o reboot.o memattr.o tpm.o
-obj-$(CONFIG_EFI) += memmap.o
+obj-$(CONFIG_EFI) += memmap.o coco.o
ifneq ($(CONFIG_EFI_CAPSULE_LOADER),)
obj-$(CONFIG_EFI) += capsule.o
endif
diff --git a/drivers/firmware/efi/coco.c b/drivers/firmware/efi/coco.c
new file mode 100644
index 000000000000..42f477d6188c
--- /dev/null
+++ b/drivers/firmware/efi/coco.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Confidential computing (coco) secret area handling
+ *
+ * Copyright (C) 2021 IBM Corporation
+ * Author: Dov Murik <[email protected]>
+ */
+
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/efi.h>
+#include <linux/init.h>
+#include <linux/memblock.h>
+#include <asm/early_ioremap.h>
+
+/*
+ * Reserve the confidential computing secret area memory
+ */
+int __init efi_coco_secret_area_reserve(void)
+{
+ struct linux_efi_coco_secret_area *secret_area;
+ unsigned long secret_area_size;
+
+ if (efi.coco_secret == EFI_INVALID_TABLE_ADDR)
+ return 0;
+
+ secret_area = early_memremap(efi.coco_secret, sizeof(*secret_area));
+ if (!secret_area) {
+ pr_err("Failed to map confidential computing secret area\n");
+ efi.coco_secret = EFI_INVALID_TABLE_ADDR;
+ return -ENOMEM;
+ }
+
+ secret_area_size = sizeof(*secret_area) + secret_area->size;
+ memblock_reserve(efi.coco_secret, secret_area_size);
+
+ pr_info("Reserved memory of EFI-provided confidential computing secret area");
+
+ early_memunmap(secret_area, sizeof(*secret_area));
+ return 0;
+}
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 847f33ffc4ae..4c1ab98cf693 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -46,6 +46,7 @@ struct efi __read_mostly efi = {
#ifdef CONFIG_LOAD_UEFI_KEYS
.mokvar_table = EFI_INVALID_TABLE_ADDR,
#endif
+ .coco_secret = EFI_INVALID_TABLE_ADDR,
};
EXPORT_SYMBOL(efi);
@@ -526,6 +527,7 @@ static const efi_config_table_type_t common_tables[] __initconst = {
#ifdef CONFIG_LOAD_UEFI_KEYS
{LINUX_EFI_MOK_VARIABLE_TABLE_GUID, &efi.mokvar_table, "MOKvar" },
#endif
+ {LINUX_EFI_COCO_SECRET_AREA_GUID, &efi.coco_secret, "CocoSecret" },
{},
};
@@ -613,6 +615,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
efi_tpm_eventlog_init();
+ efi_coco_secret_area_reserve();
+
if (mem_reserve != EFI_INVALID_TABLE_ADDR) {
unsigned long prsv = mem_reserve;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 9021dd521302..e86600af5dfd 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -550,6 +550,7 @@ extern struct efi {
unsigned long tpm_log; /* TPM2 Event Log table */
unsigned long tpm_final_log; /* TPM2 Final Events Log table */
unsigned long mokvar_table; /* MOK variable config table */
+ unsigned long coco_secret; /* Confidential computing secret table */
efi_get_time_t *get_time;
efi_set_time_t *set_time;
@@ -1189,6 +1190,8 @@ extern int efi_tpm_final_log_size;
extern unsigned long rci2_table_phys;
+extern int efi_coco_secret_area_reserve(void);
+
/*
* efi_runtime_service() function identifiers.
* "NONE" is used by efi_recover_from_page_fault() to check if the page
--
2.25.1
On Thu, Oct 14, 2021 at 01:08:47PM +0000, Dov Murik wrote:
> When efi-stub copies an EFI-provided confidential computing (coco)
> secret area, reserve that memory block for future use within the kernel.
>
> Signed-off-by: Dov Murik <[email protected]>
> ---
> arch/x86/platform/efi/efi.c | 1 +
> drivers/firmware/efi/Makefile | 2 +-
> drivers/firmware/efi/coco.c | 41 +++++++++++++++++++++++++++++++++++
> drivers/firmware/efi/efi.c | 4 ++++
> include/linux/efi.h | 3 +++
> 5 files changed, 50 insertions(+), 1 deletion(-)
> create mode 100644 drivers/firmware/efi/coco.c
>
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index 147c30a81f15..35e082e5f603 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -93,6 +93,7 @@ static const unsigned long * const efi_tables[] = {
> #ifdef CONFIG_LOAD_UEFI_KEYS
> &efi.mokvar_table,
> #endif
> + &efi.coco_secret,
Shouldn't this depend on CONFIG_EFI_SECRET?
Why build all of this code if that option is not enabled?
thanks,
greg k-h
The new efi_secret module exposes the confidential computing (coco)
EFI secret area via securityfs interface.
When the module is loaded (and securityfs is mounted, typically under
/sys/kernel/security), a "coco/efi_secret" directory is created in
securityfs. In it, a file is created for each secret entry. The name
of each such file is the GUID of the secret entry, and its content is
the secret data.
This allows applications running in a confidential computing setting to
read secrets provided by the guest owner via a secure secret injection
mechanism (such as AMD SEV's LAUNCH_SECRET command).
Removing (unlinking) files in the "coco/efi_secret" directory will zero
out the secret in memory, and remove the filesystem entry. If the
module is removed and loaded again, that secret will not appear in the
filesystem.
Signed-off-by: Dov Murik <[email protected]>
---
.../ABI/testing/securityfs-coco-efi_secret | 50 +++
drivers/virt/Kconfig | 3 +
drivers/virt/Makefile | 1 +
drivers/virt/coco/efi_secret/Kconfig | 10 +
drivers/virt/coco/efi_secret/Makefile | 2 +
drivers/virt/coco/efi_secret/efi_secret.c | 324 ++++++++++++++++++
6 files changed, 390 insertions(+)
create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret
create mode 100644 drivers/virt/coco/efi_secret/Kconfig
create mode 100644 drivers/virt/coco/efi_secret/Makefile
create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c
diff --git a/Documentation/ABI/testing/securityfs-coco-efi_secret b/Documentation/ABI/testing/securityfs-coco-efi_secret
new file mode 100644
index 000000000000..ae56976db1bc
--- /dev/null
+++ b/Documentation/ABI/testing/securityfs-coco-efi_secret
@@ -0,0 +1,50 @@
+What: security/coco/efi_secret
+Date: October 2021
+Contact: Dov Murik <[email protected]>
+Description:
+ Exposes confidential computing (coco) EFI secrets to
+ userspace via securityfs.
+
+ EFI can declare memory area used by confidential computing
+ platforms (such as AMD SEV and SEV-ES) for secret injection by
+ the Guest Owner during VM's launch. The secrets are encrypted
+ by the Guest Owner and decrypted inside the trusted enclave,
+ and therefore are not readable by the untrusted host.
+
+ The efi_secret module exposes the secrets to userspace. Each
+ secret appears as a file under <securityfs>/coco/efi_secret,
+ where the filename is the GUID of the entry in the secrets
+ table.
+
+ Two operations are supported for the files: read and unlink.
+ Reading the file returns the content of secret entry.
+ Unlinking the file overwrites the secret data with zeroes and
+ removes the entry from the filesystem. A secret cannot be read
+ after it has been unlinked.
+
+ For example, listing the available secrets::
+
+ # modprobe efi_secret
+ # ls -l /sys/kernel/security/coco/efi_secret
+ -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
+ -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
+ -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
+ -r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910
+
+ Reading the secret data by reading a file::
+
+ # cat /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910
+ the-content-of-the-secret-data
+
+ Wiping a secret by unlinking a file::
+
+ # rm /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910
+ # ls -l /sys/kernel/security/coco/efi_secret
+ -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
+ -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
+ -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
+
+ Note: The binary format of the secrets table injected by the
+ Guest Owner is described in
+ drivers/virt/coco/efi_secret/efi_secret.c under "Structure of
+ the EFI secret area".
diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
index 8061e8ef449f..fe7a6579b974 100644
--- a/drivers/virt/Kconfig
+++ b/drivers/virt/Kconfig
@@ -36,4 +36,7 @@ source "drivers/virt/vboxguest/Kconfig"
source "drivers/virt/nitro_enclaves/Kconfig"
source "drivers/virt/acrn/Kconfig"
+
+source "drivers/virt/coco/efi_secret/Kconfig"
+
endif
diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
index 3e272ea60cd9..efdb015783f9 100644
--- a/drivers/virt/Makefile
+++ b/drivers/virt/Makefile
@@ -8,3 +8,4 @@ obj-y += vboxguest/
obj-$(CONFIG_NITRO_ENCLAVES) += nitro_enclaves/
obj-$(CONFIG_ACRN_HSM) += acrn/
+obj-$(CONFIG_EFI_SECRET) += coco/efi_secret/
diff --git a/drivers/virt/coco/efi_secret/Kconfig b/drivers/virt/coco/efi_secret/Kconfig
new file mode 100644
index 000000000000..91d07366e8b0
--- /dev/null
+++ b/drivers/virt/coco/efi_secret/Kconfig
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config EFI_SECRET
+ tristate "EFI secret area securityfs support"
+ depends on EFI
+ select SECURITYFS
+ help
+ This is a driver for accessing the EFI secret area via securityfs.
+
+ To compile this driver as a module, choose M here.
+ The module will be called efi_secret.
diff --git a/drivers/virt/coco/efi_secret/Makefile b/drivers/virt/coco/efi_secret/Makefile
new file mode 100644
index 000000000000..c7047ce804f7
--- /dev/null
+++ b/drivers/virt/coco/efi_secret/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_EFI_SECRET) += efi_secret.o
diff --git a/drivers/virt/coco/efi_secret/efi_secret.c b/drivers/virt/coco/efi_secret/efi_secret.c
new file mode 100644
index 000000000000..c8b1eaba75fb
--- /dev/null
+++ b/drivers/virt/coco/efi_secret/efi_secret.c
@@ -0,0 +1,324 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * efi_secret module
+ *
+ * Copyright (C) 2021 IBM Corporation
+ * Author: Dov Murik <[email protected]>
+ */
+
+/**
+ * DOC: efi_secret: Allow reading EFI confidential computing (coco) secret area
+ * via securityfs interface.
+ *
+ * When the module is loaded (and securityfs is mounted, typically under
+ * /sys/kernel/security), a "coco/efi_secret" directory is created in
+ * securityfs. In it, a file is created for each secret entry. The name of
+ * each such file is the GUID of the secret entry, and its content is the
+ * secret data.
+ */
+
+#include <linux/seq_file.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/security.h>
+#include <linux/efi.h>
+#include <asm/cacheflush.h>
+
+#define EFI_SECRET_NUM_FILES 64
+
+#define EFI_SECRET_TABLE_HEADER_GUID \
+ EFI_GUID(0x1e74f542, 0x71dd, 0x4d66, 0x96, 0x3e, 0xef, 0x42, 0x87, 0xff, 0x17, 0x3b)
+
+struct efi_secret {
+ struct dentry *coco_dir;
+ struct dentry *fs_dir;
+ struct dentry *fs_files[EFI_SECRET_NUM_FILES];
+ struct linux_efi_coco_secret_area *secret_area;
+};
+
+/*
+ * Structure of the EFI secret area
+ *
+ * Offset Length
+ * (bytes) (bytes) Usage
+ * ------- ------- -----
+ * 0 16 Secret table header GUID (must be 1e74f542-71dd-4d66-963e-ef4287ff173b)
+ * 16 4 Length of bytes of the entire secret area
+ *
+ * 20 16 First secret entry's GUID
+ * 36 4 First secret entry's length in bytes (= 16 + 4 + x)
+ * 40 x First secret entry's data
+ *
+ * 40+x 16 Second secret entry's GUID
+ * 56+x 4 Second secret entry's length in bytes (= 16 + 4 + y)
+ * 60+x y Second secret entry's data
+ *
+ * (... and so on for additional entries)
+ *
+ * The GUID of each secret entry designates the usage of the secret data.
+ */
+
+/**
+ * struct secret_header - Header of entire secret area; this should be followed
+ * by instances of struct secret_entry.
+ * @guid: Must be EFI_SECRET_TABLE_HEADER_GUID
+ * @len: Length in bytes of entire secret area, including header
+ */
+struct secret_header {
+ efi_guid_t guid;
+ u32 len;
+} __attribute((packed));
+
+/**
+ * struct secret_entry - Holds one secret entry
+ * @guid: Secret-specific GUID (or NULL_GUID if this secret entry was deleted)
+ * @len: Length of secret entry, including its guid and len fields
+ * @data: The secret data (full of zeros if this secret entry was deleted)
+ */
+struct secret_entry {
+ efi_guid_t guid;
+ u32 len;
+ u8 data[];
+} __attribute((packed));
+
+static size_t secret_entry_data_len(struct secret_entry *e)
+{
+ return e->len - sizeof(*e);
+}
+
+static struct efi_secret the_efi_secret;
+
+static inline struct efi_secret *efi_secret_get(void)
+{
+ return &the_efi_secret;
+}
+
+static int efi_secret_bin_file_show(struct seq_file *file, void *data)
+{
+ struct secret_entry *e = file->private;
+
+ if (e)
+ seq_write(file, e->data, secret_entry_data_len(e));
+
+ return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(efi_secret_bin_file);
+
+/*
+ * Overwrite memory content with zeroes, and ensure that dirty cache lines are
+ * actually written back to memory, to clear out the secret.
+ */
+static void wipe_memory(void *addr, size_t size)
+{
+ memzero_explicit(addr, size);
+ clflush_cache_range(addr, size);
+}
+
+static int efi_secret_unlink(struct inode *dir, struct dentry *dentry)
+{
+ struct efi_secret *s = efi_secret_get();
+ struct inode *inode = d_inode(dentry);
+ struct secret_entry *e = (struct secret_entry *)inode->i_private;
+ int i;
+
+ if (e) {
+ /* Zero out the secret data */
+ wipe_memory(e->data, secret_entry_data_len(e));
+ e->guid = NULL_GUID;
+ }
+
+ inode->i_private = NULL;
+
+ for (i = 0; i < EFI_SECRET_NUM_FILES; i++)
+ if (s->fs_files[i] == dentry)
+ s->fs_files[i] = NULL;
+
+ /*
+ * securityfs_remove tries to lock the directory's inode, but we reach
+ * the unlink callback when it's already locked
+ */
+ inode_unlock(dir);
+ securityfs_remove(dentry);
+ inode_lock(dir);
+
+ return 0;
+}
+
+static const struct inode_operations efi_secret_dir_inode_operations = {
+ .lookup = simple_lookup,
+ .unlink = efi_secret_unlink,
+};
+
+static int efi_secret_map_area(void)
+{
+ struct efi_secret *s = efi_secret_get();
+ struct linux_efi_coco_secret_area *secret_area;
+ u32 secret_area_size;
+
+ if (efi.coco_secret == EFI_INVALID_TABLE_ADDR) {
+ pr_err("Secret area address is not available\n");
+ return -EINVAL;
+ }
+
+ secret_area = memremap(efi.coco_secret, sizeof(*secret_area), MEMREMAP_WB);
+ if (secret_area == NULL) {
+ pr_err("Could not map secret area header\n");
+ return -ENOMEM;
+ }
+
+ secret_area_size = sizeof(*secret_area) + secret_area->size;
+ memunmap(secret_area);
+
+ secret_area = memremap(efi.coco_secret, secret_area_size, MEMREMAP_WB);
+ if (secret_area == NULL) {
+ pr_err("Could not map secret area\n");
+ return -ENOMEM;
+ }
+
+ s->secret_area = secret_area;
+ return 0;
+}
+
+static void efi_secret_securityfs_teardown(void)
+{
+ struct efi_secret *s = efi_secret_get();
+ int i;
+
+ for (i = (EFI_SECRET_NUM_FILES - 1); i >= 0; i--) {
+ securityfs_remove(s->fs_files[i]);
+ s->fs_files[i] = NULL;
+ }
+
+ securityfs_remove(s->fs_dir);
+ s->fs_dir = NULL;
+
+ securityfs_remove(s->coco_dir);
+ s->coco_dir = NULL;
+
+ pr_debug("Removed efi_secret securityfs entries\n");
+}
+
+static int efi_secret_securityfs_setup(void)
+{
+ efi_guid_t tableheader_guid = EFI_SECRET_TABLE_HEADER_GUID;
+ struct efi_secret *s = efi_secret_get();
+ int ret = 0, i = 0, bytes_left;
+ unsigned char *ptr;
+ struct secret_header *h;
+ struct secret_entry *e;
+ struct dentry *dent;
+ char guid_str[EFI_VARIABLE_GUID_LEN + 1];
+
+ s->coco_dir = NULL;
+ s->fs_dir = NULL;
+ memset(s->fs_files, 0, sizeof(s->fs_files));
+
+ dent = securityfs_create_dir("coco", NULL);
+ if (IS_ERR(dent)) {
+ pr_err("Error creating coco securityfs directory entry err=%ld\n", PTR_ERR(dent));
+ return PTR_ERR(dent);
+ }
+ s->coco_dir = dent;
+
+ dent = securityfs_create_dir("efi_secret", s->coco_dir);
+ if (IS_ERR(dent)) {
+ pr_err("Error creating efi_secret securityfs directory entry err=%ld\n",
+ PTR_ERR(dent));
+ return PTR_ERR(dent);
+ }
+ d_inode(dent)->i_op = &efi_secret_dir_inode_operations;
+ s->fs_dir = dent;
+
+ ptr = s->secret_area->area;
+ h = (struct secret_header *)ptr;
+ if (memcmp(&h->guid, &tableheader_guid, sizeof(h->guid))) {
+ pr_err("EFI secret area does not start with correct GUID\n");
+ ret = -EINVAL;
+ goto err_cleanup;
+ }
+ if (h->len < sizeof(*h)) {
+ pr_err("EFI secret area reported length is too small\n");
+ ret = -EINVAL;
+ goto err_cleanup;
+ }
+
+ bytes_left = h->len - sizeof(*h);
+ ptr += sizeof(*h);
+ while (bytes_left >= (int)sizeof(*e) && i < EFI_SECRET_NUM_FILES) {
+ e = (struct secret_entry *)ptr;
+ if (e->len < sizeof(*e) || e->len > (unsigned int)bytes_left) {
+ pr_err("EFI secret area is corrupted\n");
+ ret = -EINVAL;
+ goto err_cleanup;
+ }
+
+ /* Skip deleted entries (which will have NULL_GUID) */
+ if (efi_guidcmp(e->guid, NULL_GUID)) {
+ efi_guid_to_str(&e->guid, guid_str);
+
+ dent = securityfs_create_file(guid_str, 0440, s->fs_dir, (void *)e,
+ &efi_secret_bin_file_fops);
+ if (IS_ERR(dent)) {
+ pr_err("Error creating efi_secret securityfs entry\n");
+ ret = PTR_ERR(dent);
+ goto err_cleanup;
+ }
+
+ s->fs_files[i++] = dent;
+ }
+ ptr += e->len;
+ bytes_left -= e->len;
+ }
+
+ pr_debug("Created %d entries in efi_secret securityfs\n", i);
+ return 0;
+
+err_cleanup:
+ efi_secret_securityfs_teardown();
+ return ret;
+}
+
+static void efi_secret_unmap_area(void)
+{
+ struct efi_secret *s = efi_secret_get();
+
+ if (s->secret_area) {
+ memunmap(s->secret_area);
+ s->secret_area = NULL;
+ }
+}
+
+static int __init efi_secret_init(void)
+{
+ int ret;
+
+ ret = efi_secret_map_area();
+ if (ret)
+ return ret;
+
+ ret = efi_secret_securityfs_setup();
+ if (ret)
+ goto err_unmap;
+
+ return ret;
+
+err_unmap:
+ efi_secret_unmap_area();
+ return ret;
+}
+
+static void __exit efi_secret_exit(void)
+{
+ efi_secret_securityfs_teardown();
+ efi_secret_unmap_area();
+}
+
+module_init(efi_secret_init);
+module_exit(efi_secret_exit);
+
+MODULE_DESCRIPTION("Confidential computing EFI secret area access");
+MODULE_AUTHOR("IBM");
+MODULE_LICENSE("GPL");
--
2.25.1
Confidential computing (coco) hardware such as AMD SEV (Secure Encrypted
Virtualization) allows a guest owner to inject secrets into the VMs
memory without the host/hypervisor being able to read them.
Firmware support for secret injection is available in OVMF, which
reserves a memory area for secret injection and includes a pointer to it
the in EFI config table entry LINUX_EFI_COCO_SECRET_TABLE_GUID.
However, OVMF doesn't force the guest OS to keep this memory area
reserved.
If EFI exposes such a table entry, efi/libstub will copy this area to a
reserved memory for future use inside the kernel.
A pointer to the new copy is kept in the EFI table under
LINUX_EFI_COCO_SECRET_AREA_GUID.
Signed-off-by: Dov Murik <[email protected]>
---
drivers/firmware/efi/libstub/Makefile | 2 +-
drivers/firmware/efi/libstub/coco.c | 68 +++++++++++++++++++++++++
drivers/firmware/efi/libstub/efi-stub.c | 2 +
drivers/firmware/efi/libstub/efistub.h | 2 +
drivers/firmware/efi/libstub/x86-stub.c | 2 +
include/linux/efi.h | 6 +++
6 files changed, 81 insertions(+), 1 deletion(-)
create mode 100644 drivers/firmware/efi/libstub/coco.c
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index d0537573501e..d77690b7dfb9 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -55,7 +55,7 @@ KCOV_INSTRUMENT := n
lib-y := efi-stub-helper.o gop.o secureboot.o tpm.o \
file.o mem.o random.o randomalloc.o pci.o \
skip_spaces.o lib-cmdline.o lib-ctype.o \
- alignedmem.o relocate.o vsprintf.o
+ alignedmem.o relocate.o vsprintf.o coco.o
# include the stub's generic dependencies from lib/ when building for ARM/arm64
efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
diff --git a/drivers/firmware/efi/libstub/coco.c b/drivers/firmware/efi/libstub/coco.c
new file mode 100644
index 000000000000..bf546b6a3f72
--- /dev/null
+++ b/drivers/firmware/efi/libstub/coco.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Confidential computing (coco) secret area handling
+ *
+ * Copyright (C) 2021 IBM Corporation
+ * Author: Dov Murik <[email protected]>
+ */
+
+#include <linux/efi.h>
+#include <linux/sizes.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+#define LINUX_EFI_COCO_SECRET_TABLE_GUID \
+ EFI_GUID(0xadf956ad, 0xe98c, 0x484c, 0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47)
+
+/**
+ * struct efi_coco_secret_table - EFI config table that points to the
+ * confidential computing secret area. The guid
+ * LINUX_EFI_COCO_SECRET_TABLE_GUID holds this table.
+ * @base: Physical address of the EFI secret area
+ * @size: Size (in bytes) of the EFI secret area
+ */
+struct efi_coco_secret_table {
+ u64 base;
+ u64 size;
+} __attribute((packed));
+
+/*
+ * Create a copy of EFI's confidential computing secret area (if available) so
+ * that the secrets are accessible in the kernel after ExitBootServices.
+ */
+void efi_copy_coco_secret_area(void)
+{
+ efi_guid_t linux_secret_area_guid = LINUX_EFI_COCO_SECRET_AREA_GUID;
+ efi_status_t status;
+ struct efi_coco_secret_table *secret_table;
+ struct linux_efi_coco_secret_area *secret_area;
+
+ secret_table = get_efi_config_table(LINUX_EFI_COCO_SECRET_TABLE_GUID);
+ if (!secret_table)
+ return;
+
+ if (secret_table->size == 0 || secret_table->size >= SZ_4G)
+ return;
+
+ /* Allocate space for the secret area and copy it */
+ status = efi_bs_call(allocate_pool, EFI_LOADER_DATA,
+ sizeof(*secret_area) + secret_table->size, (void **)&secret_area);
+
+ if (status != EFI_SUCCESS) {
+ efi_err("Unable to allocate memory for confidential computing secret area copy\n");
+ return;
+ }
+
+ secret_area->size = secret_table->size;
+ memcpy(secret_area->area, (void *)(unsigned long)secret_table->base, secret_table->size);
+
+ status = efi_bs_call(install_configuration_table, &linux_secret_area_guid, secret_area);
+ if (status != EFI_SUCCESS)
+ goto err_free;
+
+ return;
+
+err_free:
+ efi_bs_call(free_pool, secret_area);
+}
diff --git a/drivers/firmware/efi/libstub/efi-stub.c b/drivers/firmware/efi/libstub/efi-stub.c
index 26e69788f27a..18b3acd15c85 100644
--- a/drivers/firmware/efi/libstub/efi-stub.c
+++ b/drivers/firmware/efi/libstub/efi-stub.c
@@ -205,6 +205,8 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
efi_retrieve_tpm2_eventlog();
+ efi_copy_coco_secret_area();
+
/* Ask the firmware to clear memory on unclean shutdown */
efi_enable_reset_attack_mitigation();
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index cde0a2ef507d..d604c6744cef 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -858,4 +858,6 @@ efi_enable_reset_attack_mitigation(void) { }
void efi_retrieve_tpm2_eventlog(void);
+void efi_copy_coco_secret_area(void);
+
#endif
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index f14c4ff5839f..4ad85e1b6191 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -793,6 +793,8 @@ unsigned long efi_main(efi_handle_t handle,
efi_retrieve_tpm2_eventlog();
+ efi_copy_coco_secret_area();
+
setup_graphics(boot_params);
setup_efi_pci(boot_params);
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 6b5d36babfcc..9021dd521302 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -359,6 +359,7 @@ void efi_native_runtime_setup(void);
#define LINUX_EFI_MEMRESERVE_TABLE_GUID EFI_GUID(0x888eb0c6, 0x8ede, 0x4ff5, 0xa8, 0xf0, 0x9a, 0xee, 0x5c, 0xb9, 0x77, 0xc2)
#define LINUX_EFI_INITRD_MEDIA_GUID EFI_GUID(0x5568e427, 0x68fc, 0x4f3d, 0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68)
#define LINUX_EFI_MOK_VARIABLE_TABLE_GUID EFI_GUID(0xc451ed2b, 0x9694, 0x45d3, 0xba, 0xba, 0xed, 0x9f, 0x89, 0x88, 0xa3, 0x89)
+#define LINUX_EFI_COCO_SECRET_AREA_GUID EFI_GUID(0x940ed1e9, 0xd3da, 0x408b, 0xb3, 0x07, 0xe3, 0x2d, 0x25, 0x4a, 0x65, 0x16)
/* OEM GUIDs */
#define DELLEMC_EFI_RCI2_TABLE_GUID EFI_GUID(0x2d9f28a2, 0xa886, 0x456a, 0x97, 0xa8, 0xf1, 0x1e, 0xf2, 0x4f, 0xf4, 0x55)
@@ -1282,4 +1283,9 @@ static inline struct efi_mokvar_table_entry *efi_mokvar_entry_find(
}
#endif
+struct linux_efi_coco_secret_area {
+ u32 size;
+ u8 area[];
+};
+
#endif /* _LINUX_EFI_H */
--
2.25.1
On 14/10/2021 16:36, Greg KH wrote:
> On Thu, Oct 14, 2021 at 01:08:47PM +0000, Dov Murik wrote:
>> When efi-stub copies an EFI-provided confidential computing (coco)
>> secret area, reserve that memory block for future use within the kernel.
>>
>> Signed-off-by: Dov Murik <[email protected]>
>> ---
>> arch/x86/platform/efi/efi.c | 1 +
>> drivers/firmware/efi/Makefile | 2 +-
>> drivers/firmware/efi/coco.c | 41 +++++++++++++++++++++++++++++++++++
>> drivers/firmware/efi/efi.c | 4 ++++
>> include/linux/efi.h | 3 +++
>> 5 files changed, 50 insertions(+), 1 deletion(-)
>> create mode 100644 drivers/firmware/efi/coco.c
>>
>> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
>> index 147c30a81f15..35e082e5f603 100644
>> --- a/arch/x86/platform/efi/efi.c
>> +++ b/arch/x86/platform/efi/efi.c
>> @@ -93,6 +93,7 @@ static const unsigned long * const efi_tables[] = {
>> #ifdef CONFIG_LOAD_UEFI_KEYS
>> &efi.mokvar_table,
>> #endif
>> + &efi.coco_secret,
>
> Shouldn't this depend on CONFIG_EFI_SECRET?
>
> Why build all of this code if that option is not enabled?
>
Thanks Greg for noticing this. Fixed in v4 [1] where the code
is guarded with #ifdefs (so it's not built by default).
[1] https://lore.kernel.org/linux-coco/[email protected]/
-Dov