Describe the ACRN boot process and how to implement secure boot

1. Boot process and Secure boot
Sun Victor <victor.sun@intel.com>
Huang Yonghua <yonghua.huang@intel.com>
ACRN vMeet-Up Europe 2021

2. Agenda
▹Boot loader and Multiboot protocol
▹ACRN hypervisor and VMs boot
▹ACRN boot components
▹Secure boot

3. Boot loader and Multiboot protocol
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4. Boot loader
▹ A bootloader is software that is responsible for booting a computer.
▹ ACRN uses the multiboot/multiboot2 protocol to boot the hypervisor.
▹ Bootloaders supported by ACRN:
❑ GRUB 2.0x
❑ Intel Slim bootloader
❑ Self-designed UEFI-Stub
✓ under implementation for UEFI secure boot;
✓ The old version in ACRN release 2.0 only support sharing mode (industry scenario)
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5. Multiboot protocol
▹ Multiboot
▹ https://www.gnu.org/software/grub/manual/multiboot/multiboot.html
▹ Multiboot2
▹ https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html
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6. Multiboot (version 0.6.96)
▹ Support X86 only
▹ No UEFI support
▹ No kernel/module relocation support
▹ OS Image header:
❑ Magic value 0x1BADB002 in header;
❑ The header must be contained completely within the first 8192 bytes of the OS image,
and must be longword (32-bit) aligned.
▹ Machine state:
❑ EAX: Must contain the magic value 0x2BADB002;
❑ EBX: 32-bit physical address of the Multiboot information structure;
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7. Multiboot2 (version 2.0)
▹ Support more ISA (Instruction Set Architecture) like x86, MIPS, etc.
▹ UEFI support
▹ Kernel support relocation (but not for modules)
▹ OS Image header:
❑ Magic value 0xE85250D6 in header;
❑ The Multiboot2 header must be contained completely within the first 32768 bytes of
the OS image, and must be 64-bit aligned.
▹ Machine state(x86):
❑ EAX: Must contain the magic value 0x36d76289;
❑ EBX: 32-bit physical address of the Multiboot2 information structure;
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8. Multiboot support in bootloader
▹SBL support multiboot protocol only
▹GRUB 2.x support both multiboot / multiboot2 protocol
❑ “multiboot/module” command pair to support multiboot
❑ “multiboot2/module2” command pair to support multiboot2
❑ “multiboot” command might fail to boot ACRN on UEFI platform because
failed to find ACPI RSDP (it could be put anywhere per UEFI spec)
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9. Hypervisor and VMs Boot Sequence
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10. HV and Pre-launched VM boot sequence
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Native mbi
Firmware bootloader
ACRN
boot
init e820
init seed
VM boot
SBL/GRUB
Parse &
Save mbi
Saved mbi
VM
Loader
VM0
VM1
vm_config
VM Power
Management
get_saved_mbi_cmdline()
get_saved_mbi_mod(mod_id)
mod_id
boot_mode
load_type

11. Post-launched User VM boot sequence
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SOS
DM
CSE
SBL/UEFI
ACRN HV
Service VM
DM
OVMF: Initialization
Post-launched VM
OVMF: OS Loader

12. ACRN boot components
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13. ACRN boot components
▹ Multiboot kernel
❑ HV binary
▹ Multiboot modules
❑ VM kernel image
❑ VM ACPI binary (pre-launched VM only)
❑ VM ramdisk image
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14. GRUB config example
menuentry 'ACRN Multiboot1 Zephyr + Linux' {
load_video
insmod gzio
insmod part_gpt
insmod ext2
multiboot --quirk-modules-after-kernel /boot/acrn.32.out
module /boot/bzImage Linux_bzImage
module /boot/zephyr.bin Zephyr_RawImage
}
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menuentry 'ACRN Multiboot2 hybrid_rt' {
load_video
insmod gzio
insmod part_gpt
insmod ext2
multiboot2 /boot/acrn.bin
module2 /boot/uos_bzImage RT_bzImage
module2 /boot/ACPI_VM0.bin ACPI_VM0
module2 /boot/bzImage Linux_bzImage
}

15. Secure Boot
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16. Verified Boot Sequence with SBL
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DM APP2
Android VM 2
CSE
SBL
ACRN
Service VM
Kernel
Device Model
APP1
OVMF: Initialization
Guest OS
Guest VM 1
OVMF: OS Loader
Stitched as one
image
Safety OS
Kernel
multiboot
• CSE verifies SBL
• SBL verifies ACRN & Safety OS kernel
(if there is) & Service VM Kernel
• Service MV kernel verifies DM &
OVMF thru dm-verity
• OVMF starts the guest side verification
process

17. Verified Boot Sequence with UEFI/GRUB
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- CSE verifies UEFI
- UEFI verifies Shim/GRUB
- GRUB verifies ACRN, Service VM kernel and pre-launched OS kernel
- Service VM kernel verifies DM and User VM OVMF through DM-verity
- User VM OVMF starts the guest side verified boot process
UEFI
Multiboot
Device
Model
OVMF
…..
CSE
Service
VM
Kernel
Safety
OS
Kernel
Shim/
Grub
ACRN
Service VM
DM-Verity

18. Boot Sequence w/o GRUB on UEFI
(under development)
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- CSE verifies UEFI
- UEFI verifies Shim
- Shim verifies acrn.efi
- acrn.efi run efi-stub code and unpack all ACRN components
- Service VM kernel and pre-launched OS kernel
- Service VM kernel verifies DM and User VM OVMF through DM-Verity
- User VM OVMF starts the guest side verified boot process
UEFI
Device
Model
OVMF
…..
CSE
Service
VM
Kernel
Safety OS
Kernel
Shim
ACRN
Service VM
DM-Verity
EFI-
stub
acrn.efi
Packed
ACRN
compo
nents