On Tue, Jul 16, 2019 at 12:58:36PM +0200, Bastian Krause wrote:
> By default systemd generates a machine id on first boot and tries to
> persist it (see `man machine-id`). When the root file system is read-only
> systemd cannot persist the machine id. In case multiple redundant slots
> are used the machine id will vary. When not handled explicitly the
> machine id will also change during updates.
>
> It is possible to pass a machine id to the kernel which will be used by
> systemd (systemd.machine_id=).
>
> This adds functionality to pass device-specific information that will be
> hashed to generate a persistent unique machine id. The machine id will
> be finally added to the kernel parameters via the
> linux.bootargs.machine_id global variable.
>
> Note: if multiple sources provide hashable device-specific information
> (via machine_id_set_hashable()) the information provided by the last call
> prior to the late initcall set_machine_id() is used to generate the
> machine id from. Thus when updating barebox the machine id might change.
>
> Signed-off-by: Bastian Krause <bst@xxxxxxxxxxxxxx>
> ---
> common/Kconfig | 11 ++++++++
> common/Makefile | 1 +
> common/machine_id.c | 65 ++++++++++++++++++++++++++++++++++++++++++++
> include/machine_id.h | 6 ++++
> 4 files changed, 83 insertions(+)
> create mode 100644 common/machine_id.c
> create mode 100644 include/machine_id.h
>
> diff --git a/common/Kconfig b/common/Kconfig
> index 8aad5baecd..4b2d79350d 100644
> --- a/common/Kconfig
> +++ b/common/Kconfig
> @@ -982,6 +982,17 @@ config RESET_SOURCE
> of the reset and why the bootloader is currently running. It can be
> useful for any kind of system recovery or repair.
>
> +config MACHINE_ID
> + bool "pass machine-id to kernel"
> + depends on FLEXIBLE_BOOTARGS
> + select DIGEST
> + select DIGEST_SHA1_GENERIC
> + help
> + Sets the linux.bootargs.machine_id global variable with a value of
> + systemd.machine_id=UID. The UID is a persistent device-specific
> + id. It is a hash over device-specific information provided by various
> + sources.
> +
> endmenu
>
> menu "Debugging"
> diff --git a/common/Makefile b/common/Makefile
> index a284655fc1..10960169f9 100644
> --- a/common/Makefile
> +++ b/common/Makefile
> @@ -11,6 +11,7 @@ obj-y += bootsource.o
> obj-$(CONFIG_ELF) += elf.o
> obj-y += restart.o
> obj-y += poweroff.o
> +obj-$(CONFIG_MACHINE_ID) += machine_id.o
> obj-$(CONFIG_AUTO_COMPLETE) += complete.o
> obj-y += version.o
> obj-$(CONFIG_BAREBOX_UPDATE) += bbu.o
> diff --git a/common/machine_id.c b/common/machine_id.c
> new file mode 100644
> index 0000000000..54c1820086
> --- /dev/null
> +++ b/common/machine_id.c
> @@ -0,0 +1,65 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2019 Pengutronix, Bastian Krause <kernel@xxxxxxxxxxxxxx>
> + */
> +
> +#define pr_fmt(fmt) "machine-id: " fmt
> +
> +#include <common.h>
> +#include <init.h>
> +#include <digest.h>
> +#include <globalvar.h>
> +#include <crypto/sha.h>
> +#include <machine_id.h>
> +
> +#define MACHINE_ID_LENGTH 32
> +
> +static void *__machine_id_hashable;
> +static size_t __machine_id_hashable_length;
> +
> +
> +void machine_id_set_hashable(void *hashable, size_t len)
const void *
> +{
> + __machine_id_hashable = hashable;
> + __machine_id_hashable_length = len;
You should make a copy rather than storing the pointer.
> +}
> +
> +static int machine_id_set_bootarg(void)
> +{
> + struct digest *digest = NULL;
> + unsigned char machine_id[SHA1_DIGEST_SIZE];
> + char *hex_id;
> + int ret = 0;
> +
> + if (!__machine_id_hashable) {
> + pr_warn("No hashable set, will not pass id to kernel\n");
I don't think this is worth a warning. With this series this will be
issued for example on all non i.MX6 boards enabled in imx_v7_defconfig.
> + goto out;
> + }
> +
> + hex_id = "systemd.machine_id=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
This string should be treated const, better allocate hex_id.
> +
> + digest = digest_alloc_by_algo(HASH_ALGO_SHA1);
> + ret = digest_init(digest);
> + if (ret)
> + goto out;
> +
> + ret = digest_update(digest, &__machine_id_hashable,
> + __machine_id_hashable_length);
You are hashing the address of the __machine_id_hashable pointer here.
> + if (ret)
> + goto out;
> +
> + ret = digest_final(digest, machine_id);
> + if (ret)
> + goto out;
> +
> + /* use the first 16 bytes of the sha1 hash as the machine-id */
> + bin2hex(&hex_id[19], &machine_id[0], MACHINE_ID_LENGTH/2);
> +
> + globalvar_add_simple("linux.bootargs.machine_id", &hex_id[0]);
> +
> +out:
> + digest_free(digest);
> + return ret;
> +
> +}
> +late_initcall(machine_id_set_bootarg);
> diff --git a/include/machine_id.h b/include/machine_id.h
> new file mode 100644
> index 0000000000..e4a9dacd4d
> --- /dev/null
> +++ b/include/machine_id.h
> @@ -0,0 +1,6 @@
> +#ifndef __MACHINE_ID_H__
> +#define __MACHINE_ID_H__
> +
> +void machine_id_set_hashable(void *hashable, size_t len);
You should add a static inline wrapper for CONFIG_MACHINE_ID disabled.
Sascha
--
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