Re: [PATCH 1/2] Create Nix derivation for building verity images

Demi Marie Obenour
2025-11-06T10:55:32Z

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On 11/6/25 05:20, Alyssa Ross wrote:
> Demi Marie Obenour <demiobenour@gmail.com> writes:
>
>> This gets rid of a lot of duplicated code and allows building the verity
>> roothash and superblock only when needed. It also removes a hack used
>> to work around make limitations. Furthermore,
>> 'veritysetup --root-hash-file' is used to avoid an awk script.
>>
>> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
>> ---
>> nix-shell --pure --run 'make run' in host/initramfs fails. This is a
>> preexisting bug and I will send a separate patch for it.
>> ---
>> host/initramfs/Makefile | 25 +++++--------------------
>> host/initramfs/shell.nix | 4 +++-
>> host/rootfs/Makefile | 24 +++++-------------------
>> host/rootfs/shell.nix | 3 +++
>> host/verity.nix | 19 +++++++++++++++++++
>> lib/common.mk | 1 -
>> pkgs/default.nix | 1 +
>> release/live/Makefile | 26 +++++---------------------
>> release/live/default.nix | 4 +++-
>> 9 files changed, 44 insertions(+), 63 deletions(-)
>
>> diff --git a/host/rootfs/Makefile b/host/rootfs/Makefile
>> index 00d125774bb7b98736d0928c69cb307740cee034..bb602e2745fb5873204f453b35fc529c5c96f64a 100644
>> --- a/host/rootfs/Makefile
>> +++ b/host/rootfs/Makefile
>> @@ -82,25 +82,11 @@ clean:
>> rm -rf build
>> .PHONY: clean
>>
>> -# veritysetup format produces two files, but Make only (portably)
>> -# supports one output per rule, so we combine the two outputs then
>> -# define two more rules to separate them again.
>> -build/rootfs.verity: $(dest)
>> - $(VERITYSETUP) format $(dest) build/rootfs.verity.superblock.tmp \
>> - | awk -F ':[[:blank:]]*' '$$1 == "Root hash" {print $$2; exit}' \
>> - > build/rootfs.verity.roothash.tmp
>> - cat build/rootfs.verity.roothash.tmp build/rootfs.verity.superblock.tmp \
>> - > $@
>> - rm build/rootfs.verity.roothash.tmp build/rootfs.verity.superblock.tmp
>> -build/rootfs.verity.roothash: build/rootfs.verity
>> - head -n 1 build/rootfs.verity > $@
>> -build/rootfs.verity.superblock: build/rootfs.verity
>> - tail -n +2 build/rootfs.verity > $@
>>
>> -build/live.img: ../../scripts/format-uuid.sh ../../scripts/make-gpt.sh ../../scripts/sfdisk-field.awk build/rootfs.verity.superblock build/rootfs.verity.roothash $(dest)
>> +build/live.img: ../../scripts/format-uuid.sh ../../scripts/make-gpt.sh ../../scripts/sfdisk-field.awk $(ROOT_FS_VERITY) $(ROOT_FS_VERITY_ROOTHASH) $(dest)
>> ../../scripts/make-gpt.sh $@.tmp \
>> - build/rootfs.verity.superblock:verity:$$(../../scripts/format-uuid.sh "$$(dd if=build/rootfs.verity.roothash bs=32 skip=1 count=1 status=none)") \
>> - $(dest):root:$$(../../scripts/format-uuid.sh "$$(head -c 32 build/rootfs.verity.roothash)")
>> + "$$ROOT_FS_VERITY:verity:$$(../../scripts/format-uuid.sh "$$(dd "if=$$ROOT_FS_VERITY_ROOTHASH" bs=32 skip=1 count=1 status=none)")" \
>> + $(dest):root:$$(../../scripts/format-uuid.sh "$$(head -c 32 "$$ROOT_FS_VERITY_ROOTHASH")")
>> mv $@.tmp $@
>>
>> debug:
>> @@ -110,7 +96,7 @@ debug:
>> $(VMLINUX)
>> .PHONY: debug
>>
>> -run: build/live.img $(EXT_FS) build/rootfs.verity.roothash
>> +run: build/live.img $(EXT_FS) $(ROOT_FS_VERITY_ROOTHASH)
>> @set -x && \
>> ext="$$(mktemp build/spectrum-rootfs-extfs.XXXXXXXXXX.img)" && \
>> truncate -s 10G "$$ext" && \
>> @@ -131,7 +117,7 @@ run: build/live.img $(EXT_FS) build/rootfs.verity.roothash
>> -device virtconsole,chardev=virtiocon0 \
>> -drive file=build/live.img,if=virtio,format=raw,readonly=on \
>> -drive file=/proc/self/fd/3,if=virtio,format=raw \
>> - -append "earlycon console=hvc0 roothash=$$(< build/rootfs.verity.roothash) intel_iommu=on nokaslr" \
>> + -append "earlycon console=hvc0 roothash=$$(< "$$ROOT_FS_VERITY_ROOTHASH") intel_iommu=on nokaslr" \
>> -device virtio-keyboard \
>> -device virtio-mouse \
>> -device virtio-gpu \
>> diff --git a/host/rootfs/shell.nix b/host/rootfs/shell.nix
>> index 1bf61bebf418333624e799cc8ca231f5783206f4..f16e4905adfbc8faebde19d0a1364ad9df90219b 100644
>> --- a/host/rootfs/shell.nix
>> +++ b/host/rootfs/shell.nix
>> @@ -5,6 +5,7 @@
>> import ../../lib/call-package.nix (
>> { callSpectrumPackage, rootfs, pkgsStatic, srcOnly, stdenv
>> , btrfs-progs, cryptsetup, jq, netcat, qemu_kvm, reuse, util-linux
>> +, verity
>> }:
>>
>> rootfs.overrideAttrs (
>> @@ -20,5 +21,7 @@ rootfs.overrideAttrs (
>> KERNEL = "${passthru.kernel}/${stdenv.hostPlatform.linux-kernel.target}";
>> LINUX_SRC = srcOnly passthru.kernel.configfile;
>> VMLINUX = "${passthru.kernel.dev}/vmlinux";
>> + ROOT_FS_VERITY = "${verity}/rootfs.verity.superblock";
>> + ROOT_FS_VERITY_ROOTHASH = "${verity}/rootfs.verity.roothash";
>> };
>> })) (_: {})
>
> Surely this would break interactive development of the rootfs?
> If I'm in a Nix shell, and make a change to any part of the rootfs, the
> verity data in the environment will be out of date. I'd have to leave
> and re-enter the Nix shell after /any/ change, waiting for an evaluation
> each time, as opposed to the current situation where that's only
> necessary when modifying Nix code or other Spectrum components.

It would. Are there alternatives you can recommend? I don't want the
updater and the installer to have to use two different copies.
--
Sincerely,
Demi Marie Obenour (she/her/hers)

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