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

Alyssa Ross
2025-11-06T11:44:43Z

[-- Attachment #1: Type: text/plain, Size: 5838 bytes --]

Demi Marie Obenour <demiobenour@gmail.com> writes:

> 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.

Have the host/rootfs derivation install the verity files alongside the
rootfs image. Then host/rootfs/Makefile is the single place we generate
the verity images, and it will still be regenerated by make when in a
Nix shell.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 227 bytes --]