Speculation on How EFI was Modified:

By simply having Ring 0 (kernel mode) one can place EFI variables into NVRAM via EFI runtime services.  If one of these variables is scanned as a valid FFV, that gives execute at level of Ring -1, from there modifying the SPI contents of the flash chip to re-write the Intel ME / Intel Gigabit Ethernet is possible.  By flashing an old version of the Intel ME (orbetter the Intel AMT) one can take advantage of known CVEs in the Intel ME giving Ring -3.  From here one can inject any SMBios of their choosing and maintain Ring -2 every boot.  This allows for a evil actor to run their own stack during any OS load or reinstall.  By using AMT ramdisks, EFI drivers, and modifying the ACPI tables they can then live in Ring 0 cooperatively with any OS that is installed.

Booting Into a Decent Shell

After some working around various issues I finally got into a decent EFI v2.2 shell.  The first five entries in the handle table were what are known as “FFV” or flash-firmware-volume entries.  This implies that the lion share of this is happening one of two ways: the flash chip has been somehow updated to a version of EFI that it should not contain, or two that something is persisting to disk and performing a restore in a way that it is not possible to reset with only pulling the power cable out of the device.  It is clearly running vPro and the AMT stack, and has created an entry of a ramdisk entry (shows in the table) as well as loading a number of drivers and Dxe’s that are to say the least, unexpected.
From a running linux view the following EFI vars were observed, not matching in any way what was pulled from the shell: https://gist.githubusercontent.com/rickmark/21059379ab65c11bfcb2f3b339bdbea1/raw/7a0d2a60f38cdc1bf7887df1e7e461474dced25c/refi_var_list.txt

• PlatformLangCodes = en-US;x-UQI
• ItkModifiedSetup = 0
• MeInfoSetup
• SIO_DEV_STATUS_VAR
• VV_SIO_LD0
• DriverHlthEnable
• TpmServFlatgs
• OptaneState
• FPDT_Volatile
• NBPlatformData
• E770BB69-BCB4-4D09-9E97-23FF9456FEAC:SystemAccess = 0
• BootDebugPolicyApplied
• CurrentPolicy
• CurrentActivePolicy
• 1C697A091199_IAIDPXE
• Ip6Config:16697A091199
• IPv4Config2:1C697A091199
• SetupCpuFetures

• StandardGUID 8BE4DF61-93CA-11D2-AA0D-00E098032B9C
• ACA9F304-21E1-4852-9875-7FF488AD67A5
• PCI_COMMON
• 7B59104A-C00D-4158-87FF-F03D6396A915
• SecureBootSetup
• EC87D643-EBA4-4BB5-A1E5-3F3E36B20DA9
• SdioDevConfiguration
• 64192DCA-D034-49D2-A6DE-65A829EB4C74
• `IccAdvancedSetupDataVar
• 5432122D-D034-29D2-A6DE-65A829EB4C74
• MeSetupStorage
• 90D93E09-4E91-4B3D-8C77-C82FF10E3C81
• CpuSmm
• 05A798EA-39EE-40FC-92C5-622582FA634B

Asking the device for the listing of devices shows

The following does skip some entries as there’s no good way to copy and paste this, and UDIDs are hard…

• LoadedImage DxeCore
• 5CB5C776-
• Decompress
• FirmwareVolume2 -B9A42172CE53
• FirmwareVolume2 -EC40C23C5916
• FirmwareVolume2 -DC1671C10F36
• FirmwareVolume2 -E48809A7ACE3
• FirmwareVolume2 -2A4FF6CA6FE5
• EE4E5898-
• LoadedImage StatusCodeDxe
• 36232936-
• SmartCardReader RscHandler
• LoadedImage PcdDxe
• GetPcdInfo GetPcdInfoProtocol Pcd Pcd
• LoadedImage CpuIo2Dxe
• CpuIo2
• LoadedImage FlashDriver
• 755B6596-
• LoadedImage NvramDxe
• VariableWriteArch VariableArch
• MonotonicCounterArch
• LoadedImage CrbDxe
• LoadedImage FastBootRuntime
• LoadedImage DxeBoardConfigInit
• LoadedImage WdtDxe
• LoadedImage CmosDxe
• 9851740C-
• LoadedImage RomLayoutDxe
• HiiPackageList LoadedImage Bds
• BdsArch
• LoadedImage DataHubDxe
• AE80D021-
• LoadedImage DevicePathDxe
• DevicePathFromText DevicePathToText DevicePathUtilities
• DebugSupport EBCInterpreter LoadedImage EbcDxe
• LoadedImage HiiDatabase
• HIIImage ConfigKeywordHandler HIIConfigRouting HIIDatabase HIIString HIIFont
• LoadedImage SecurityStubDxe
• SecurityArch Security2Arch
• LoadedImage TimestampDxe
• Timestamp
• LoadedImage CpuDxe
• LoadedImage CpuIoDxe
• B0732526-
• LoadedImage AmiCpuFeaturesDxe
• LoadedImage AmiPciPlatform
• PciPlatform
• DebugPort LoadedImage GopDebugDxe
• LoadedImage WdtAppDxe
• LoadedImage PlatformInfoDxe
• LoadedImage PolicyInitDxe
• LoadedImage AmiSyncSetupData
• LoadedImage CpuInitDxe
• E223CF65-
• LoadedImage SmmAccess
• SmmAccess2
• LoadedImage LegacyInterrupt
• 31CE593d-
• LoadedImage PchSmbusDxe
• SmbusHc
• LoadedImage FspWrapperNotifyDxe
• LoadedImage Aint31
• LoadedImage Acoustic
• 10E9D800-
• LoadedImage S3SaveStateDxe
• S3SaveState
• LoadedImage SioDxeInit
• 9D36F7EF-
• LoadedImage IdeBusBoard
• LoadedImage PciDxeInit
• EC63428D-
• LoadedImage RdspPlus
• ComponentName2 DriverBinding LoadedImage Uhcd
• 2AD8E2D2-
• ComponentName2 DriverBinding
• ComponentName2 DriverBinding
• LoadedImage DpcDxe
• 480F8AE9-
• LoadedImage AmiBoardInfo2
• 4FC0733F-
• LoadedImage FanDxe
• LoadedImage HddSecurity
• CE6F86BB-
• LoadedImage EsrtDxe
• A340C064-
• LoadedImage OpalSecurity
• 59AF16B0-
• LoadedImage RngDxe
• Rng
• LoadedImage AmiRedFishApi
• B5E7C7AF-
• LoadedImage AmiDeviceGuardApi
• DAEEAFC8-
• LoadedImage TpmSmbiosDxe
• LoadedImage TpmNvmeSupport
• LoadedImage TcgStorageSecurity
• 734AA01D-
• LoadedImage UpdateDriverProtocol
• LoadedImage CpuDxe
• CpuArch
• MpService
• LoadedImage DxeSignBiosAuthenticate
• 24400798-
• LoadedImage EventLog
• DAED23EC-
• LoadedImage IntelVBios2
• HIIFormBrowser2
• 49374A18-
• HIIFormBrowser2
• 1F73B18D-
• 348C4D62-
• BEBF428C-
• LoadedImage FsDxe
• LoadedImage DnsrDxe
• ComponentName2 DriverBinding LoadedImage NTFS
• LoadedImage CapsuleRuntimeDxe
• CapsuleArch
• LoadedImage RuntimeDxe
• RuntimeArch
• MetronomeArch LoadedImage SbRun
• RealTimeClockArch
• SmmControl2 LoadedImage SmmControl
• LoadedImage MePlatformReset
• ResetArch
• LoadedImage CryptoDXE
• ComponentName2 DriverBinding LoadedImage NTFS
• DriverBinding LoadedImage MouseDriver
• LoadedImage StdDefaultsUpdate
• LoadedImage Achi
• 83: CompnentName2 DriverBinding
• LoadedImage HttpUtilitiesDxe
• HttpUtilities
• LoadedImage Nvme
• ComponentName2 DriverBinding
• LoadedImage SecureBootDXE
• LoadedImage TcgPlatformSetupPolicy
• LoadedImage ITK50
• LoadedImage CISDWdtDxe
• LoadedImage OCDxe
• LoadedImage OemGop
• LoadedImage NbDxe
• LoadedImage AmiTxtDxe
• LoadedImage HstiIhvDxe
• LoadedImage TxtDxe
• LoadedImage PciHostBridgeDxe
• PciHostBridgeResourceAllocation
• PCIRootBridgeIO DevicePath(PciRoot(0x0))
• LoadedImage AmiUpdateCspResources
• 27CFAC87-
• LoadedImage PchSpiRuntime
• 00C7D289-
• LoadedImage SiInitDxe
• IncompatiblePciDeviceSupport
• LoadedImage HpetTimerDxe
• TimerArch
• HiiPackageList LoadedImage AmiHsti
• AdapterInfo(AdapterInfo)
• LoadedImage ACPI
• AcpiSdt AcpiTable
• 01FA319E-
• LoadedImage AcpiS3SaveDxe
• HiiPackageList LoadedImage PciOutOfResourcesSetupPage
• LoadedImage UsbRtDxe
• HiiPackageList LoadedImage HddSmart
• 9401BD4F-
• HiiPackageList LoadedImage PauseKey
• LoadedImage SmbiosBoard
• HiiPackageList LoadedImage Tpm20PlatformDxe
• LoadedImage CpuS3DataDxe
• LoadedImage PlatformConfigDxe
• C298B206-
• 23F2D944-
• HiiPackageList ICBDTSEPopupMenu
• HiiPackageList LoadedImage HkUpdate
• E2E6CF23-
• HiiPackageList LoadedImage PlatformIdPage
• HIIConfigAccess
• LoadedImage OemBoardDxe
• BA8D58AB-
• LoadedImage PiSmmIpl
• LoadedImage PiSmmCore
• SmmCommunication SmmBase2
• LoadedImage Tcg2Dxe
• LoadedImage StatusCodeDxe
• LoadedImage FlashDriverSmm
• ECB867AB-
• LoadedImage CpuIo2Smm
• LoadedImage SmmLockBox
• BD445d79-
• LoadedImage PchSmbusSmm
• LoadedImage SraSmmStub
• LoadedImage AhciSmm
• LoadedImage CryptoCMM
• 91ABC830-
• LoadedImage SmmS3SaveState
• LoadedImage RuntimeSmm
• 395C33FE-
• LoadedImage PiSmmCpuDxeSmm
• SmmConfig
• LoadedImage NvramSmm
• CD3D0A05-
• LoadedImage PchSpiSmm
• LoadedImage SmmPcieSataController
• LoadedImage SbDxe
• WatchdogTimerArch
• 17706D27-
• PciHotPlugInit
• 377E6D6B-
• LoadedImage CnvUefiVariables
• C77AE557-
• LoadedImage Dptf
• LoadedImage HstiResultDxe
• LoadedImage TbtDxe
• 4D6A54D1-
• LoadedImage PlatoformVTdSampleDxe
• 3D17E448-
• LoadedImage PlatformSetup
• D5E1268B- D4D2F201-
• LoadedImage PowerMgmtDxe
• D71DB106-
• LoadedImage BdatAccessHandler
• LoadedImage PchInitDxe
• LoadedImage SraDxe
• 7AE12E27-
• LoadedImage HeciInit
• EC7BC880-
• 1498D127-
• LoadedImage BootScriptExecutorDxe
• LoadedImage HardwareSignatureEntry
• 43169678-
• ComponentName DriverBinding LoadedImage RtkSdCardDxe
• LoadedImage Smbios
• LoadedImage OEMActivation
• LoadedImage OemUsbPort
• LoadedImage OemEventDxe
• LoadedImage SaInitDxe
• LegacyRegion2
• 9E67AECF-
• 603DF7CA-
• LoadedImage AcpiPlatform
• C77AE556-
• LoadedImage AcpiDebugDxe
• LoadedImage RamDiskDxe
• HIIConfigAccess DevicePath -BB1A4F94081E
• HIIConfigAccess DevicePath -2B769AAA30C5
• F7: 28A03FF4- RamDisk
• LoadedImage ItkSmmVarsDxe
• LoadedImage ItkSmmVarsDxe
• LoadedImage PchSmiDispatcher
• LoadedImage CpuSpSMI
• LoadedImage NbSmi
• LoadedImage PowerButton
• LoadedImage SbRunSmm
• LoadedImage SleepSmi
• FF: LoadedImage PeriodicSmiControl
• LoadedImage TcoSmi
• LoadedImage AcpiModeEnable
• LoadedImage PepBccdSmm
• LoadedImage TbtSmm
• LoadedImage OverClockSmiHandler
• LoadedImage PowerMgmtSmm
• LoadedImage SaLateInitSmm
• 0D66A1CF- LoadedImage PchInitSmm
• LoadedImage UsbRtSmm
• LoadedImage CmosSmm
• LoadedImage SmmHddSecurity
• LoadedImage NvmeSmm
• LoadedImage SdioSmm
• LoadedImage TpmClearOnRollbackSmm
• LoadedImage SmmTcgStorageSec
• LoadedImage CrbSmi
• LoadedImage PiSmmCommunicationSmm
• LoadedImage RtcWakeup
• LoadedImage ItkSmmVars
• LoadedImage OemBoardSmi
• LoadedImage SmmPlatoform
• ImageDevicePath -AB74D2C1A600 LoadedImage EnglishDxe
• UnicodeCollation2 UnicodeCollation
• LoadedImage SmbiosUpdateData
• LoadedImage AmiMemoryInfoConfig
• LoadedImage MeSmbiosDxe
• ComponentName2 ComponentName DriverBinding ImageDevicePath -CD92CFB7D362 LoadedImage SataController
• LoadedImage PlatofrmInitDxe
• LoadedImage VtioDxe
• LoadedImage DxeOverClock
• LoadedImage MeFwDowngrade
• 3EA824D1-
• LoadedImage ConSplitter
• ComponentName2 DriverBinding
• ComponentName2 DriverBinding
• AbsolutePointer SimplePointer SimpleTextInEx SimpleTextIn SimpleTextOut
• LoadedImage GraphicsConsole
• ComponentName2 DriverBinding
• ComponentName2 ComponentName DriverBinding LoadedImage DiskIoDxe
• ComponentName2 ComponentName DriverBinding LoadedImage PartitionDxe
• LoadedImage RstOneClickEnable
• LoadedImage RstuefiDriverSupport
• 5B10CDC8-
• SupportedEfiSpecVersion(0x0002001E) ComponentName2 ComponentnName DriverBinding LoadedImage IntegratedTouch
• LoadedImage GenericSio
• 7576CC89- ComponentName2 DriverBinding
• LoadedImage IdeBusSrc
• 132: ComponentName2 DriverBinding
• LoadedImage PciBus
• ComponentName2 DriverBinding
• LoadedImage Ps2Main
• ComponentName2 DriverBindding
• ComponentName2 ComponentName DriverBinding LoadedImage SnpDxe
• ComponentName2 ComponentName DriverBinding LoadedImage MnpDxe
• ComponentName2 ComponentName DriverBinding LoadedImage ArpDxe
• ComponentName2 ComponentName DriverBinding LoadedImage IpSecDxe
• IpSec2 IpSecConfig
• ComponentName2 ComponentName DriverBinding
• ComponentName2 ComponentName DriverBinding LoadedImage TcpDxe
• ComponentName2 ComponentName DriverBinding
• 13F:
• ComponentName2 ComponentName DriverBinding LoadedImage UefiPxeBcDxe
• ComponentName2 ComponentName DriverBinding
• ComponentName2 ComponentName DriverBinding LoadedImage DnsDxe
• ComponentName2 ComponentName DriverBinding
• LoadedImage TlsDxe
• TlsServiceBinding
• ComponentName2 ComponentName DriverBinding LoadedImage Dhcp4Dxe
• ComponentName2 ComponentName DriverBinding LoadedImage Ip4Dxe
• ComponentName2 ComponentName DriverBinding LoadedImage Mtftp4Dxe
• ComponentName2 ComponentName DriverBinding LoadedImage Udp4Dxe
• ComponentName2 ComponentName DriverBinding LoadedImage Ip6Dxe
• ComponentName2 ComponentName DriverBinding LoadedImage Udp6Dxe
• ComponentName2 ComponentName DriverBinding LoadedImage Mtftp6Dxe
• LoadedImage AtaPassThru
• C6734411-
• LoadedImage AudioPlayback
• ComponentName2 ComponentName DriverBinding LoadedImage Fat
• AuthenticationInfo iSCSIInitiatorName ComponentName2 ComponentName DriverBinding LoadedImage IScsiDxe
• ComponentName2 ComponentName DriverBinding
• HIIConfigAccess DevicePath(-CCAD2E0F4CF9)
• ComponentName2 ComponentName DriverBinding LoadedImage ScsiBus
• ComponentName2 ComponentName DriverBinding LoadedImage ScsiDisk
• LoadedImage PcieSataController
• ComponentName2 DriverBinding
• ComponentName2 DriverBinding
• ComponentName2 DriverBinding LoadedImage SdioDriver
• LoadedImage AcpiPlatformFeatures
• LoadedImage CustomSMBIOS
• HiiPackageList LoadedImage AMITSE
• HiiPopup
• 160: LoadedImage SmmGenericSio
• LoadedImage UpdateMemoryRecord
• EDIDOverride
• PciEnumerationComplete
• 30249499- C7D4703B-
• 651B7EBD- DBCB2FCD- ComponentName2 DriverBinding ImageDevicePath((0x3,0x75F5A018,0x75F6BA98)) LoadedImage MemoryMapped
• 3279A703-
• AD77AE29- 1FD29BE6- AtaPassThru
• 1FD29BE6- AD77AE29
• FA20568B-
• 6DE538E4-
• A33319B5-
• A33319B5-
• DevicePath LoadFile
• ImageDevicePath LoadedImage SmbiosMisc
• ImageDevicePath LoadedImage FileExplorerLite
• 088C3203-
• HiiPackageList ImageDevicePath LoadedImage DpsdSetup
• HIIConfigAccess DevicePtah
• BootManagerPolicy
• A68D1FDE-
• 4622F942-
• HIIConfigAccess DevicePath
• 3A3300AB-
• F8DD3A9D-
• F31FCBB5-
• 348C4D62-
• 18F: 348C4D62-
• 348C4D62-
• AdapterInfo(AdapterInfo)
• 0F500BE6-
• 8D9B3387-
• Shell ShellParameters SimpleTextOut ImageDevicePath LoadedImage()
• PciEnumerationComplete F42A009D-
• USBHostController2 USBHostController 3279A703- DevicePath(PciRoot(0x0)/Pci(0x14,0x0)) PCIIO
• 0ADFB62D- SimpleTextInEx SimpleTextIn 1FEDE521- DevicePath(..)/Pci(0x14,0x0)/USB(0x0,0x0)) USBIO
• 198: SimplePointer 1FEDE521- DevicePath(..)/Pci(0x14,0x0)/USB(0x0,0x1)) USBIO
• DevicePath(..)/Pci(0x014,0x0)/USB(0x0,0x2)) USBIO
• 30249499- C7D3703B- LoadFile2 BusSpecificDriverOverride DevicePath(PciRoot(0x0)/Pci(0x2,0x0)) PCIIO
• E1E4A857- SimpleTextOut EDIDActive(EDIDActive GraphicsOutput(GraphicsOutput) EDIDDiscovered(EDIDDiscovered) 39487C79- DevicePath(..0x2,0x0)/AcpiAdr(0x80013310))
• DevicePath(PciRoot(0x0)/Pci(0x0,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x8,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x12,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x14,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x16,0x0)) PCIIO
• FDB29BE6- AD77AE29- AtaPassThru B2FA4764- IdeControllerInit DevicePath(PciRoot(0x0)/Pci(0x17,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x1D,0x0)) PCIIO
• 4B235191- 1FD29BE6- AD77AE29- F4F63529- NvmExpressPassThru AFA4CF3F-DevicePath(..)/Pci(0x1D,0x0)/Pci(0x0,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x1F,0x0)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x1F,0x4)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x1F,0x5)) PCIIO
• DevicePath(PciRoot(0x0)/Pci(0x1F,0x6)) PCIIO
• DiskIO F4F63529- BlockIO DickInfo DevicePath(..17,0x0)/Sata(0x2,0xFFFF,0x0))
• 1A1: DickIO E6D6D379- PartitionInfo BlockIO DevicePath(..49E6173E12,0x800,0x7470658F))
• DiskIO BlockIO DiskInfo DevicePath(..0x1,8D-73-B0-91-55-38-26-00)) StorageSecurityCommand
• SimpleFileSystem DiskIO EFISystemPartition PartitionInfo BlockIO DevicePath(..-FFC0339F3A57,0x800,0xEE000))
• DiskIO 0FC63DAF- PartitionInfo BlockIO DevicePath(..78C7D5369,0xEE800,0x12A0800))
• 1A7: DiskIO E6D6D379- PartitionInfo BlockIo DevicePath(.. 18EF8D,0x138F000,0x38FF6800))

Open Questions:

• How does the EFI Runtime Services pointer get passed from EFI boot-loaders to the kernel?  Or does it re-scan ACPI to pick it up?
• Why does the kernel have an option for performing an ACPI SSDT overlay from an EFI variable?
• Will a EFI variable containing a EFI FFV (flash firmware volume) or FFS (flash file system) be picked up as part of the EFI payload?  Would this allow for early injection of additional DXE’s into the runtime environment before exiting EFI to the boot-loader?
• For what possible reason did someone think it was a good idea to have an NVMe over TCP and other fabric protocol?  This seems to be in use as the device also showed up with a wwn or “World Wide Name” ala iSCSI.
• What is required to enable AMT on a device that was not intended for it?
• For what reason would a firewire and cdrom kernel module get injected into initrd?
• Why would there be a script in initrd that creates systemd units that are later deleted?
• Why would a network controller be brought up 3 times with the name WMI identity when virtualization of the adapter is not in use
• Why would network address families be brought up so early in the process if not to access the root filesystem across a synthetic network fabric?
• Why would seccomp be creating eBPF LSM executables without any other audit record?
• Why would one override the ACPI tables for Intel WiFi compliance if not to use frequency bands from other countries in the US to evade detection?
• Why would a bluetooth based braile TTY attempt to come up if not a side channel for access to the machine?
• Why would kernel objects on a clean Arch install (*.zko) files be signed with an ephemeral key if not tampered with?
• Why is there a “bluetooth meshing” driver
• Why is the EC able to perform interrupt pausing and resumption - during normal operation of the Intel ME it doesn’t interfere with normal OS operations in this way.
• Why would there be two tpm objects if not a root and a synthetic device?  Or perhaps a dTPM while the system has also enabled a fTPM (both occur at path ACPI LNXSYSTM:00-LNXSYBUS:00-MSFT0101:00 which makes reference to the Microsoft ACPI table
• Can dleyna be used as a form of remote desktop?
• What is slsh?
• Why does the SATA device occur at ata3-host2-target2 - and why is ata1/2 “DUMMY”
• Why does the network device occur at address PCI 0000:00-0000:00:1f.6 and not .0?  Are these IO-SRV virtual functions?
• Why are the TTYs platform-serial8250 which is a hardware backed device rather then a psudo terminal
• Why did a /var/lib/machines mount come up and later die?
• Why is there a binfmt_misc that gets brought up with the system
• Why are there kernel trace file system mounts?
• What is systemd-ask-password-console.path and systemd-ask-password-wall.path
• Why would there be an on shutdown service mkinitcpio-generate-shutdown-ramfs.service as this should only happen upon kernel updates via pacman.  It runs with TMPDIR=/run and /usr/bin/mkinitcpio -A sd-shutdown -k none -c /dev/null -d /run/initramfs
• What is shaddow.service and why does it have to run to change or verify passwd and shaddow - both of which have clearly been edited as they contain a vi trailing “-” pair.  Seems to execute `/usr/binpwck -r || r=1; /usr/bin/grpck -r`
• What systemd-boot-system-token.service do?
• What are the getty-pre.target doing?
• Why is remote-fs.target a thing, it also includes verity and cryptsetup
• Somehow “RealtimeKit” is a name collision on linux and apple ecosystems?  Also what happened to remoteprocfor the Intel EC
• Why is udisks2 being used as a fuse helper for most things
• Why does my initrd have a /usr mount (initrd-usr-fs.target) - clearly this is being loaded across some other busbecause I have no /usr but do have a /usr/local in my fstab
• What is request-key.conf and why does it have to many defined values for debug and dns_resolver, it also seems to make special consideration o debug:loop:*
• What is “Rygel Remote UI Server”
• Secure TTY config makes reference to hvc0 - probably some hypervisor based channel
• it also allows the tty[1-6], ttyS0 and console
• 
  

Useful non-Network Control Channels

Using accessibility systems like brltty over bluetooth can give terminal access without need of a reliable network (WiFior ethernet).

Early Injection using Firewire Serial

Messing with the ACPI Tables

People often forget that operating systems will happily collect data from ACPI including AML code.  This is usually executed during power events like suspend and resume and has been abused in the past in the form of “dark wake” attacks.

Hiding from Root Using the Linux BFP LSM

One of the more recent advancements in the Linux tree is reusing eBPF (yes of note because it has been used for network firewalls for many years) to become a policy agent.  eBPF was selected because it is a Turing complete language that we already compile and execute in-kernel by way of ip_tables/x_tables and the like.
When auditing is enabled, loading and unloading of these BPF programs will become part of the kernel debug output so they can be observed.  You can actually “mount” this to see the BPF entries by executing mount bpffs /mnt/bpffs/ -t bpf which will provide maps.debug and progs.debug.  Another useful tool to get more information about this is bpftool prog show

Xen Para-virtualization is Still a Thing

Even without using Intel’s VT, it is still very possible for an attacker to kexec into a Xen based kernel providing themselves a way to control non-virtual ring-0 even while still letting an arbitrary linux guest OS execute thinking it is the kernel of the system.  Even without kexec one can do about exactly the same thing using kgdb after transferring an image to memory.

Tampering During Compile

• sync_regs()
• mce_setup()
• do_machine_check()
• rcu_nmi_enter()