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Use deterministic salt for AVB footer of prebuilt boot img

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When target specified a prebuilt boot.img, current build system will add
avb hash footer to it with a random salt. Use a deterministic salt
instead for more reproducible builds. To stay consistent with
non-prebuilt boot.img code path, we extract the kernel image from
prebuilt boot.img and uses sha256sum of kernel image as the salt.

Test: th
Bug: 293313353
Change-Id: I988999ddc4f18e0b8677b05a3165c847b6a11b52
This commit is contained in:
Kelvin Zhang 2023-10-17 12:27:56 -07:00
parent 6787354f96
commit 160762a276
3 changed files with 15 additions and 2 deletions
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6
core/Makefile
View file

@ -1444,15 +1444,19 @@ INTERNAL_PREBUILT_BOOTIMAGE := $(BOARD_PREBUILT_BOOTIMAGE)
INSTALLED_BOOTIMAGE_TARGET := $(PRODUCT_OUT)/boot.img
ifeq ($(BOARD_AVB_ENABLE),true)
$(INSTALLED_BOOTIMAGE_TARGET): $(INTERNAL_PREBUILT_BOOTIMAGE) $(AVBTOOL) $(BOARD_AVB_BOOT_KEY_PATH)
$(INSTALLED_BOOTIMAGE_TARGET): PRIVATE_WORKING_DIR := $(call intermediates-dir-for,PACKAGING,prebuilt_bootimg)
$(INSTALLED_BOOTIMAGE_TARGET): $(INTERNAL_PREBUILT_BOOTIMAGE) $(AVBTOOL) $(BOARD_AVB_BOOT_KEY_PATH) $(UNPACK_BOOTIMG)
cp $(INTERNAL_PREBUILT_BOOTIMAGE) $@
$(UNPACK_BOOTIMG) --boot_img $(INTERNAL_PREBUILT_BOOTIMAGE) --out $(PRIVATE_WORKING_DIR)
chmod +w $@
$(AVBTOOL) add_hash_footer \
--image $@ \
--salt `sha256sum $(PRIVATE_WORKING_DIR)/kernel | cut -d " " -f 1` \
$(call get-partition-size-argument,$(BOARD_BOOTIMAGE_PARTITION_SIZE)) \
--partition_name boot $(INTERNAL_AVB_BOOT_SIGNING_ARGS) \
$(BOARD_AVB_BOOT_ADD_HASH_FOOTER_ARGS)
$(call declare-container-license-metadata,$(INSTALLED_BOOTIMAGE_TARGET),SPDX-license-identifier-GPL-2.0-only SPDX-license-identifier-Apache-2.0,restricted notice,$(BUILD_SYSTEM)/LINUX_KERNEL_COPYING build/soong/licenses/LICENSE,"Boot Image",bool)
$(call declare-container-license-deps,$(INSTALLED_BOOTIMAGE_TARGET),$(INTERNAL_PREBUILT_BOOTIMAGE),$(PRODUCT_OUT)/:/)

1
core/config.mk
View file

@ -722,6 +722,7 @@ else
BUILD_SUPER_IMAGE := $(BOARD_CUSTOM_BUILD_SUPER_IMAGE)
endif
IMG_FROM_TARGET_FILES := $(HOST_OUT_EXECUTABLES)/img_from_target_files$(HOST_EXECUTABLE_SUFFIX)
UNPACK_BOOTIMG := $(HOST_OUT_EXECUTABLES)/unpack_bootimg
MAKE_RECOVERY_PATCH := $(HOST_OUT_EXECUTABLES)/make_recovery_patch$(HOST_EXECUTABLE_SUFFIX)
OTA_FROM_TARGET_FILES := $(HOST_OUT_EXECUTABLES)/ota_from_target_files$(HOST_EXECUTABLE_SUFFIX)
OTA_FROM_RAW_IMG := $(HOST_OUT_EXECUTABLES)/ota_from_raw_img$(HOST_EXECUTABLE_SUFFIX)

10
tools/releasetools/common.py
View file

@ -1947,7 +1947,15 @@ def _SignBootableImage(image_path, prebuilt_name, partition_name,
cmd = [avbtool, "add_hash_footer", "--image", image_path,
"--partition_size", str(part_size), "--partition_name",
partition_name]
AppendAVBSigningArgs(cmd, partition_name)
# Use sha256 of the kernel as salt for reproducible builds
with tempfile.TemporaryDirectory() as tmpdir:
RunAndCheckOutput(["unpack_bootimg", "--boot_img", image_path, "--out", tmpdir])
for filename in ["kernel", "ramdisk", "vendor_ramdisk00"]:
path = os.path.join(tmpdir, filename)
if os.path.exists(path) and os.path.getsize(path):
with open(path, "rb") as fp:
salt = sha256(fp.read()).hexdigest()
AppendAVBSigningArgs(cmd, partition_name, salt)
args = info_dict.get("avb_" + partition_name + "_add_hash_footer_args")
if args and args.strip():
split_args = ResolveAVBSigningPathArgs(shlex.split(args))