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

[Demi Marie Obenour <demiobenour@gmail.com>]

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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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