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diff --git a/Lessons/Lesson_19/README.md b/Lessons/Lesson_19/README.md new file mode 100644 index 0000000..65e5cb2 --- /dev/null +++ b/Lessons/Lesson_19/README.md @@ -0,0 +1,186 @@ +In this lesson we would be messing with the NVRAM variables (BIOS settings), i.e. variables that are persistent between boots. + +As you remember after OVMF build we have these files: +``` +$ ls -l Build/OvmfX64/RELEASE_GCC5/FV/OVMF* +-rw-r--r-- 1 kostr kostr 4194304 Jun 25 14:40 Build/OvmfX64/RELEASE_GCC5/FV/OVMF.fd +-rw-r--r-- 1 kostr kostr 3653632 Jun 25 14:40 Build/OvmfX64/RELEASE_GCC5/FV/OVMF_CODE.fd +-rw-r--r-- 1 kostr kostr 540672 Jun 25 14:38 Build/OvmfX64/RELEASE_GCC5/FV/OVMF_VARS.fd +``` +- `OVMF_CODE.fd` - code image (read-only) +- `OVMF_VARS.fd` - NVRAM variables image (read-write) +- `OVMF.fd` - combined image (`OVMF_CODE.fd` + `OVMF_VARS.fd`) + +We can boot QEMU either with: +``` +$ qemu-system-x86_64 -drive if=pflash,format=raw,file=Build/OvmfX64/RELEASE_GCC5/FV/OVMF.fd \ + ... +``` +or with +``` +$ qemu-system-x86_64 -drive if=pflash,format=raw,readonly,file=Build/OvmfX64/RELEASE_GCC5/FV/OVMF_CODE.fd \ + -drive if=pflash,format=raw,file=Build/OvmfX64/RELEASE_GCC5/FV/OVMF_VARS.fd \ + ... +``` + +It was fine to use short form earlier, but in this lesson we would modify NVRAM variables, so it is best to use full form with a separate copy of `OVMF_VARS.fd`, so you could always revert things to their initial state. + +Let's undo our modifications to the `OvmfPkg` package and rebuild it: +``` +$ git restore OvmfPkg +$ build --platform=OvmfPkg/OvmfPkgX64.dsc --arch=X64 --buildtarget=RELEASE --tagname=GCC5 +``` + +After that create a backup copy of `OVMF_VARS.fd` and run QEMU with it: +``` +$ cp Build/OvmfX64/RELEASE_GCC5/FV/OVMF_VARS.fd ../ +$ qemu-system-x86_64 -drive if=pflash,format=raw,readonly,file=Build/OvmfX64/RELEASE_GCC5/FV/OVMF_CODE.fd \ + -drive if=pflash,format=raw,file=../OVMF_VARS.fd \ + -drive format=raw,file=fat:rw:~/UEFI_disk \ + -nographic \ + -net none +``` + +Check boot variables with the help of `bcfg boot dump`: +``` +Shell> bcfg boot dump +Option: 00. Variable: Boot0000 + Desc - UiApp + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331) + OVMF_VARS.fdiOptional- N +Option: 01. Variable: Boot0001 + Desc - UEFI QEMU DVD-ROM QM00003 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 02. Variable: Boot0002 + Desc - UEFI QEMU HARDDISK QM00001 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 03. Variable: Boot0003 + Desc - EFI Internal Shell + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(7C04A583-9E3E-4F1C-AD65-E05268D0B4D1) + Optional- N +``` + +Besides showing boot options `bcfg` command can add/remove boot options or change their order. +You can check out help for `bcfg` via: +``` +bcfg -? -b +``` + +Now let's try to add our `InteractiveApp.efi` to the boot options. + +``` +Shell> fs0: +FS0:\> bcfg boot add 4 InteractiveApp.efi "Interactive app" +Target = 0004. +bcfg: Add Boot0004 as 4 +FS0:\> bcfg boot dump +Option: 00. Variable: Boot0000 + Desc - UiApp + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331) + Optional- N +Option: 01. Variable: Boot0001 + Desc - UEFI QEMU DVD-ROM QM00003 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 02. Variable: Boot0002 + Desc - UEFI QEMU HARDDISK QM00001 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 03. Variable: Boot0003 + Desc - EFI Internal Shell + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(7C04A583-9E3E-4F1C-AD65-E05268D0B4D1) + Optional- N +Option: 04. Variable: Boot0004 + Desc - Interactive app + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)/\InteractiveApp.efi + Optional- N +``` + +Now if you navigate to the `Boot Manager` you'll see our app: + + +As soon as you don't change `OVMF_VARS.fd` this option would be present even between QEMU restarts. + +We can go further and even place our app as a first boot source: +``` +Shell> bcfg boot mv 4 0 +Shell> bcfg boot dump +Option: 00. Variable: Boot0004 + Desc - Interactive app + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)/\InteractiveApp.efi + Optional- N +Option: 01. Variable: Boot0000 + Desc - UiApp + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331) + Optional- N +Option: 02. Variable: Boot0001 + Desc - UEFI QEMU DVD-ROM QM00003 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 03. Variable: Boot0002 + Desc - UEFI QEMU HARDDISK QM00001 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 04. Variable: Boot0003 + Desc - EFI Internal Shell + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(7C04A583-9E3E-4F1C-AD65-E05268D0B4D1) + Optional- N +``` + +Now if you reboot UEFI shell with a `reset` command, or rerun QEMU, you will need to pass our app before you can go to the BIOS menu: +``` +BdsDxe: loading Boot0004 "Interactive app" from PciRoot(0x0)/Pci(0x1,0x1)/Ata(Primary,Master,0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)/\InteractiveApp.efi +BdsDxe: starting Boot0004 "Interactive app" from PciRoot(0x0)/Pci(0x1,0x1)/Ata(Primary,Master,0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)/\InteractiveApp.efi +Try to guess the secret symbol! +``` + +Input correct symbol, go to the `Boot manager` menu and run UEFI shell so we could delete our app from the boot sources: +``` +FS0:\> bcfg boot dump +Option: 00. Variable: Boot0004 + Desc - Interactive app + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)/\InteractiveApp.efi + Optional- N +Option: 01. Variable: Boot0000 + Desc - UiApp + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331) + Optional- N +Option: 02. Variable: Boot0001 + Desc - UEFI QEMU DVD-ROM QM00003 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 03. Variable: Boot0002 + Desc - UEFI QEMU HARDDISK QM00001 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 04. Variable: Boot0003 + Desc - EFI Internal Shell + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(7C04A583-9E3E-4F1C-AD65-E05268D0B4D1) + Optional- N + +FS0:\> bcfg boot rm 0 + +FS0:\> bcfg boot dump +Option: 00. Variable: Boot0000 + Desc - UiApp + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331) + Optional- N +Option: 01. Variable: Boot0001 + Desc - UEFI QEMU DVD-ROM QM00003 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 02. Variable: Boot0002 + Desc - UEFI QEMU HARDDISK QM00001 + DevPath - PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0) + Optional- Y +Option: 03. Variable: Boot0003 + Desc - EFI Internal Shell + DevPath - Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(7C04A583-9E3E-4F1C-AD65-E05268D0B4D1) + Optional- N +``` + + + + |