[PATCH Part1 RFC v3 20/22] x86/boot: Add Confidential Computing address to setup_header

Brijesh Singh
2021-06-02T14:06:13Z

While launching the encrypted guests, the hypervisor may need to provide
some additional information that will used during the guest boot. In the
case of AMD SEV-SNP the information includes the address of the secrets
and CPUID pages. The secrets page contains information such as a VM to
PSP communication key and CPUID page contain PSP filtered CPUID values.

When booting under the EFI based BIOS, the EFI configuration table
contains an entry for the confidential computing blob. In order to support
booting encrypted guests on non EFI VM, the hypervisor to pass these
additional information to the kernel with different method.

For this purpose expand the struct setup_header to hold the physical
address of the confidential computing blob location. Being zero means it
isn't passed.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
Documentation/x86/boot.rst | 27 +++++++++++++++++++++++++++
arch/x86/boot/header.S | 7 ++++++-
arch/x86/include/uapi/asm/bootparam.h | 1 +
3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
index fc844913dece..9b32805617bb 100644
--- a/Documentation/x86/boot.rst
+++ b/Documentation/x86/boot.rst
@@ -75,6 +75,8 @@ Protocol 2.14 BURNT BY INCORRECT COMMIT
DO NOT USE!!! ASSUME SAME AS 2.13.

Protocol 2.15 (Kernel 5.5) Added the kernel_info and kernel_info.setup_type_max.
+
+Protocol 2.16 (Kernel 5.14) Added the confidential computing blob address
============= ============================================================

.. note::
@@ -226,6 +228,7 @@ Offset/Size Proto Name Meaning
0260/4 2.10+ init_size Linear memory required during initialization
0264/4 2.11+ handover_offset Offset of handover entry point
0268/4 2.15+ kernel_info_offset Offset of the kernel_info
+026C/4 2.16+ cc_blob_address Physical address of the confidential computing blob
=========== ======== ===================== ============================================

.. note::
@@ -1026,6 +1029,30 @@ Offset/size: 0x000c/4

This field contains maximal allowed type for setup_data and setup_indirect structs.

+============ ==================
+Field name: cc_blob_address
+Type: write (optional)
+Offset/size: 0x26C/4
+Protocol: 2.16+
+============ ==================
+
+ This field can be set by the boot loader to tell the kernel the physical address
+ of the confidential computing blob info.
+
+ A value of 0 indicates that either the blob is not provided or use the EFI configuration
+ table to retrieve the blob location.
+
+ In the case of AMD SEV the blob look like this::
+
+ struct cc_blob_sev_info {
+ u32 magic; /* 0x45444d41 (AMDE) */
+ u16 version;
+ u16 reserved;
+ u64 secrets_phys; /* pointer to secrets page */
+ u32 secrets_len;
+ u64 cpuid_phys; /* pointer to cpuid page */
+ u32 cpuid_len;
+ }

The Image Checksum
==================
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 6dbd7e9f74c9..b4a014a18f91 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -303,7 +303,7 @@ _start:
# Part 2 of the header, from the old setup.S

.ascii "HdrS" # header signature
- .word 0x020f # header version number (>= 0x0105)
+ .word 0x0210 # header version number (>= 0x0105)
# or else old loadlin-1.5 will fail)
.globl realmode_swtch
realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
@@ -577,6 +577,11 @@ pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr
init_size: .long INIT_SIZE # kernel initialization size
handover_offset: .long 0 # Filled in by build.c
kernel_info_offset: .long 0 # Filled in by build.c
+cc_blob_address: .long 0 # (Header version 0x210 or later)
+ # If nonzero, a 32-bit pointer to
+ # the confidential computing blob.
+ # The blob will contain the information
+ # used while booting the encrypted VM.

# End of setup header #####################################################

diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index b25d3f82c2f3..210e1a0fb4ce 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -102,6 +102,7 @@ struct setup_header {
__u32 init_size;
__u32 handover_offset;
__u32 kernel_info_offset;
+ __u32 cc_blob_address;
} __attribute__((packed));

struct sys_desc_table {
--
2.17.1