[PATCH v7 1/5] efi: Save location of EFI confidential computing area

Dov Murik
2022-02-01T12:45:04Z

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.

If EFI exposes such a table entry, uefi_init() will keep a pointer to
the EFI config table entry in efi.coco_secret, so it can be used later
by the kernel (specifically drivers/virt/coco/efi_secret). It will also
appear in the kernel log as "CocoSecret=ADDRESS"; for example:

[ 0.000000] efi: EFI v2.70 by EDK II
[ 0.000000] efi: CocoSecret=0x7f22e680 SMBIOS=0x7f541000 ACPI=0x7f77e000 ACPI 2.0=0x7f77e014 MEMATTR=0x7ea0c018

The new functionality can be enabled with CONFIG_EFI_COCO_SECRET=y.

Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
---
arch/x86/platform/efi/efi.c | 3 +++
drivers/firmware/efi/Kconfig | 16 ++++++++++++++++
drivers/firmware/efi/efi.c | 6 ++++++
include/linux/efi.h | 10 ++++++++++
4 files changed, 35 insertions(+)

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 147c30a81f15..1591d67e0bcd 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -93,6 +93,9 @@ static const unsigned long * const efi_tables[] = {
#ifdef CONFIG_LOAD_UEFI_KEYS
&efi.mokvar_table,
#endif
+#ifdef CONFIG_EFI_COCO_SECRET
+ &efi.coco_secret,
+#endif
};

u64 efi_setup; /* efi setup_data physical address */
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 2c3dac5ecb36..6fa251b3709f 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -284,3 +284,19 @@ config EFI_CUSTOM_SSDT_OVERLAYS

See Documentation/admin-guide/acpi/ssdt-overlays.rst for more
information.
+
+config EFI_COCO_SECRET
+ bool "EFI Confidential Computing Secret Area Support"
+ depends on EFI
+ help
+ Confidential Computing platforms (such as AMD SEV) allow the
+ Guest Owner to securely inject secrets during guest VM launch.
+ The secrets are placed in a designated EFI reserved memory area.
+
+ In order to use the secrets in the kernel, the location of the secret
+ area (as published in the EFI config table) must be kept.
+
+ If you say Y here, the address of the EFI secret area will be kept
+ for usage inside the kernel. This will allow the
+ virt/coco/efi_secret module to access the secrets, which in turn
+ allows userspace programs to access the injected secrets.
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 7de3f5b6e8d0..378d044b2463 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -46,6 +46,9 @@ struct efi __read_mostly efi = {
#ifdef CONFIG_LOAD_UEFI_KEYS
.mokvar_table = EFI_INVALID_TABLE_ADDR,
#endif
+#ifdef CONFIG_EFI_COCO_SECRET
+ .coco_secret = EFI_INVALID_TABLE_ADDR,
+#endif
};
EXPORT_SYMBOL(efi);

@@ -528,6 +531,9 @@ static const efi_config_table_type_t common_tables[] __initconst = {
#endif
#ifdef CONFIG_LOAD_UEFI_KEYS
{LINUX_EFI_MOK_VARIABLE_TABLE_GUID, &efi.mokvar_table, "MOKvar" },
+#endif
+#ifdef CONFIG_EFI_COCO_SECRET
+ {LINUX_EFI_COCO_SECRET_AREA_GUID, &efi.coco_secret, "CocoSecret" },
#endif
{},
};
diff --git a/include/linux/efi.h b/include/linux/efi.h
index ccd4d3f91c98..771d4cd06b56 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -405,6 +405,7 @@ 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(0xadf956ad, 0xe98c, 0x484c, 0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47)

/* OEM GUIDs */
#define DELLEMC_EFI_RCI2_TABLE_GUID EFI_GUID(0x2d9f28a2, 0xa886, 0x456a, 0x97, 0xa8, 0xf1, 0x1e, 0xf2, 0x4f, 0xf4, 0x55)
@@ -596,6 +597,7 @@ 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;
@@ -1335,4 +1337,12 @@ extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
static inline void efifb_setup_from_dmi(struct screen_info *si, const char *opt) { }
#endif

+struct linux_efi_coco_secret_area {
+ u64 base_pa;
+ u64 size;
+};
+
+/* Header of a populated EFI secret area */
+#define EFI_SECRET_TABLE_HEADER_GUID EFI_GUID(0x1e74f542, 0x71dd, 0x4d66, 0x96, 0x3e, 0xef, 0x42, 0x87, 0xff, 0x17, 0x3b)
+
#endif /* _LINUX_EFI_H */
--
2.25.1