Re: [PATCH v3 3/6] bootm: Support boot measurement

Simon Glass
2023-01-12T23:44:18Z

Hi Eddie,

On Thu, 12 Jan 2023 at 09:16, Eddie James <eajames@linux.ibm.com> wrote:
>
> Add a configuration option to measure the boot through the bootm
> function. Add the measurement state to the booti and bootz paths
> as well.
>
> Signed-off-by: Eddie James <eajames@linux.ibm.com>
> ---
> boot/Kconfig | 23 ++++++++++++++++
> boot/bootm.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++
> cmd/booti.c | 1 +
> cmd/bootm.c | 2 ++
> cmd/bootz.c | 1 +
> include/bootm.h | 2 ++
> include/image.h | 1 +
> 7 files changed, 100 insertions(+)
>
> diff --git a/boot/Kconfig b/boot/Kconfig
> index 30bc182fcd..e90d61412e 100644
> --- a/boot/Kconfig
> +++ b/boot/Kconfig
> @@ -587,6 +587,29 @@ config LEGACY_IMAGE_FORMAT
> loaded. If a board needs the legacy image format support in this
> case, enable it here.
>
> +config MEASURED_BOOT
> + bool "Measure boot images and configuration to TPM and event log"
> + depends on HASH && TPM_V2
> + help
> + This option enables measurement of the boot process. Measurement
> + involves creating cryptographic hashes of the binary images that
> + are booting and storing them in the TPM. In addition, a log of
> + these hashes is stored in memory for the OS to verify the booted
> + images and configuration. Enable this if the OS has configured
> + some memory area for the event log and you intend to use some
> + attestation tools on your system.
> +
> +if MEASURED_BOOT
> + config MEASURE_DEVICETREE
> + bool "Measure the devicetree image"
> + default y if MEASURED_BOOT
> + help
> + On some platforms, the devicetree is not static as it may contain
> + random MAC addresses or other such data that changes each boot.
> + Therefore, it should not be measured into the TPM. In that case,
> + disable the measurement here.
> +endif # MEASURED_BOOT
> +
> config SUPPORT_RAW_INITRD
> bool "Enable raw initrd images"
> help
> diff --git a/boot/bootm.c b/boot/bootm.c
> index 15fce8ad95..c8423f2c60 100644
> --- a/boot/bootm.c
> +++ b/boot/bootm.c
> @@ -22,6 +22,7 @@
> #include <asm/global_data.h>
> #include <asm/io.h>
> #include <linux/sizes.h>
> +#include <tpm-v2.h>
> #if defined(CONFIG_CMD_USB)
> #include <usb.h>
> #endif
> @@ -659,6 +660,72 @@ int bootm_process_cmdline_env(int flags)
> return 0;
> }
>
> +int bootm_measure(struct bootm_headers *images)
> +{
> + int ret = 0;
> +
> + /* Skip measurement if EFI is going to do it */
> + if (images->os.os == IH_OS_EFI &&
> + IS_ENABLED(CONFIG_EFI_TCG2_PROTOCOL) &&
> + IS_ENABLED(CONFIG_BOOTM_EFI))
> + return ret;
> +
> + if (IS_ENABLED(CONFIG_MEASURED_BOOT)) {

Isn't this an EFI feature? I would expect MEASURED_BOOT to be a
generic U-Boot feature that can be used by non-EFI code.

So I believe what we need here is some sort of API for measuring
things, enabled by MEASURED_BOOT, with EFI providing its
implementation (in lib/efi_loader/). Driver model would be a good
approach I think, or perhaps a linker list as is done with the
environment / partitions?

In any case, adding EFI code into bootm is a non-starter.

The first thing is to define what the API is, e.g. with a header file
called measured_boot.h or similar.

> + struct tcg2_event_log elog;
> + struct udevice *dev;
> + void *initrd_buf;
> + void *image_buf;
> + const char *s;
> + u32 rd_len;
> +
> + ret = tcg2_measurement_init(&dev, &elog);
> + if (ret)
> + return ret;
> +
> + image_buf = map_sysmem(images->os.image_start,
> + images->os.image_len);
> + ret = tcg2_measure_data(dev, &elog, 8, images->os.image_len,
> + image_buf, EV_COMPACT_HASH,
> + strlen("linux") + 1, (u8 *)"linux");
> + if (ret)
> + goto unmap_image;
> +
> + rd_len = images->rd_end - images->rd_start;
> + initrd_buf = map_sysmem(images->rd_start, rd_len);
> + ret = tcg2_measure_data(dev, &elog, 8, rd_len, initrd_buf,
> + EV_COMPACT_HASH, strlen("initrd") + 1,
> + (u8 *)"initrd");
> + if (ret)
> + goto unmap_initrd;
> +
> + if (IS_ENABLED(CONFIG_MEASURE_DEVICETREE)) {
> + ret = tcg2_measure_data(dev, &elog, 9, images->ft_len,
> + (u8 *)images->ft_addr,
> + EV_TABLE_OF_DEVICES,
> + strlen("dts") + 1,
> + (u8 *)"dts");
> + if (ret)
> + goto unmap_initrd;
> + }
> +
> + s = env_get("bootargs");
> + if (!s)
> + s = "";
> + ret = tcg2_measure_data(dev, &elog, 1, strlen(s) + 1, (u8 *)s,
> + EV_PLATFORM_CONFIG_FLAGS,
> + strlen(s) + 1, (u8 *)s);
> +
> +unmap_initrd:
> + unmap_sysmem(initrd_buf);
> +
> +unmap_image:
> + unmap_sysmem(image_buf);
> + tcg2_measurement_term(dev, &elog, ret != 0);
> + }
> +
> + return ret;
> +}
> +
> /**
> * Execute selected states of the bootm command.
> *
> @@ -710,6 +777,9 @@ int do_bootm_states(struct cmd_tbl *cmdtp, int flag, int argc,
> if (!ret && (states & BOOTM_STATE_FINDOTHER))
> ret = bootm_find_other(cmdtp, flag, argc, argv);
>
> + if (IS_ENABLED(CONFIG_MEASURED_BOOT) && !ret && (states & BOOTM_STATE_MEASURE))
> + bootm_measure(images);
> +
> /* Load the OS */
> if (!ret && (states & BOOTM_STATE_LOADOS)) {
> iflag = bootm_disable_interrupts();
> diff --git a/cmd/booti.c b/cmd/booti.c
> index 6ac39193db..659bb10549 100644
> --- a/cmd/booti.c
> +++ b/cmd/booti.c
> @@ -127,6 +127,7 @@ int do_booti(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
> #ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
> BOOTM_STATE_RAMDISK |
> #endif
> + BOOTM_STATE_MEASURE |
> BOOTM_STATE_OS_PREP | BOOTM_STATE_OS_FAKE_GO |
> BOOTM_STATE_OS_GO,
> &images, 1);
> diff --git a/cmd/bootm.c b/cmd/bootm.c
> index 37c2af96e0..0c4a713e02 100644
> --- a/cmd/bootm.c
> +++ b/cmd/bootm.c
> @@ -161,6 +161,8 @@ int do_bootm(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
> BOOTM_STATE_OS_GO;
> if (IS_ENABLED(CONFIG_SYS_BOOT_RAMDISK_HIGH))
> states |= BOOTM_STATE_RAMDISK;
> + if (IS_ENABLED(CONFIG_MEASURED_BOOT))
> + states |= BOOTM_STATE_MEASURE;
> if (IS_ENABLED(CONFIG_PPC) || IS_ENABLED(CONFIG_MIPS))
> states |= BOOTM_STATE_OS_CMDLINE;
> ret = do_bootm_states(cmdtp, flag, argc, argv, states, &images, 1);
> diff --git a/cmd/bootz.c b/cmd/bootz.c
> index f1423573d2..87922bfc3c 100644
> --- a/cmd/bootz.c
> +++ b/cmd/bootz.c
> @@ -81,6 +81,7 @@ int do_bootz(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
> #ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
> BOOTM_STATE_RAMDISK |
> #endif
> + BOOTM_STATE_MEASURE |
> BOOTM_STATE_OS_PREP | BOOTM_STATE_OS_FAKE_GO |
> BOOTM_STATE_OS_GO,
> &images, 1);
> diff --git a/include/bootm.h b/include/bootm.h
> index 044a4797ed..06d8b1acd8 100644
> --- a/include/bootm.h
> +++ b/include/bootm.h
> @@ -55,6 +55,8 @@ ulong bootm_disable_interrupts(void);
> int bootm_find_images(int flag, int argc, char *const argv[], ulong start,
> ulong size);
>
> +int bootm_measure(struct bootm_headers *images);
> +
> int do_bootm_states(struct cmd_tbl *cmdtp, int flag, int argc,
> char *const argv[], int states, struct bootm_headers *images,
> int boot_progress);
> diff --git a/include/image.h b/include/image.h
> index bed75ce1b3..bd74e74a75 100644
> --- a/include/image.h
> +++ b/include/image.h
> @@ -407,6 +407,7 @@ struct bootm_headers {
> #define BOOTM_STATE_OS_FAKE_GO 0x00000200 /* 'Almost' run the OS */
> #define BOOTM_STATE_OS_GO 0x00000400
> #define BOOTM_STATE_PRE_LOAD 0x00000800
> +#define BOOTM_STATE_MEASURE 0x00001000
> int state;
>
> #if defined(CONFIG_LMB) && !defined(USE_HOSTCC)
> --
> 2.31.1
>

Regards,
Simon