Re: How to boot FreeBSD for arm 32 bit as DomU with u-boot on my ARM Chromebook

---> As I understand, it makes sure that u-boot keeps in secure mode during
boot and passes control to ubldr, which boots FreeBSD kernel, in that mode.

Can you elaborate your sentence more ? I know that the bootloader secure
mode is bypassed by the virtual open systems u-boot. Are you saying that
when the control passes to the second u-boot,it will happen in secure
mode,so that the bypass that happened loading the first u-boot,is annulled
? If this is true,maybe can I boot FreeBSD using the virtual-open-system
custom u-boot ? Is this compatible with FreeBSD ? Where can I find the
u-boot.bin that the xen developer talked about ? thanks bro'.



On Sun, Dec 17, 2023 at 12:35 AM Stanislav Silnicki <
stanislav.silnicki@mailgate.us> wrote:

> Hi Mario,
>
> U-Boot  beast is hiding in this den:
> https://source.denx.de/u-boot/u-boot.git
> I took a brief look at your post and it seems to me, that option
> CONFIG_CMO_BY_VA_ONLY is irrelevant to your target armv7 32 bit platform:
> https://source.denx.de/u-boot/u-boot/-/blob/master/arch/arm/cpu/armv8/Kconfig?ref_type=heads#L3
>
> As for compiling the u-boot, it is a doable task, given that you
> understand what you are doing. There are no specific options in u-boot
> devoted to FreeBSD. It is a boot loader, whose mission to make basic
> hardware initialization, read you kernel file from some media into RAM and
> then pass it control.
>
> Basically, you can grab some defconfig, prepared for any other Exynos5250
> based board  (say, this one:
> https://source.denx.de/u-boot/u-boot/-/blob/master/configs/arndale_defconfig?ref_type=heads)
> and adopt it somehow.
>
> As per my experience, you have to respect these two options, compiling
> u-boot for FreeBSD:
> https://github.com/freebsd/freebsd-ports/blob/main/sysutils/u-boot-master/files/FreeBSD_Fragment
>
> As I understand, it makes sure, that u-boot keeps in secure mode during
> boot and passes control to ubldr, which boots FreBSD kernel, in that mode.
> Otherwise, there a lot of surprises you may realize.
>
> Hope, this will help to progress you tasks
> Stan
>
> Mario Marietto wrote:
>
>
> Hello.
>
> I'm trying to boot FreeBSD for arm32 bit as DomU on my ARM Chromebook.
> Basically there are two ways to accomplish this task :
>
> 1) to write a patch that allows the FreeBSD kernel to boot as a zImage
> file. This could be accomplished applying this patch to a specific file
> that's on the source code of FreeBSD :
>
>
>
> https://xenbits.xen.org/gitweb/?p=p...8;hb=0782e25d98cc1391472717035f986c979edef0c9
> <https://xenbits.xen.org/gitweb/?p=people/julieng/freebsd.git;a=blob_plain;f=sys/arm/conf/XENVIRT;h=ff6433392e6fc2d5fa7c1ad1f7c40155003af9a8;hb=0782e25d98cc1391472717035f986c979edef0c9>
>
>
> This patch was written by Julien Grall a lot of time ago and now it does
> not work anymore. This is the reason :
>
>
> It appears FreeBSD-CURRENT removed the last step converting the kernel
> file to kernel.bin. The patch can be readily rebased, but without
> kernel.bin that doesn't do too much.
>
>
>
> So,without a rebase of that patch the first option is not applicable. And
> I'm not able to fix it.
>
> 2) booting FreeBSD using U-Boot,as explained to me by a xen developer :
>
>
> I was trying to explain why and how Julien's patch works so that you could
> be the one to re-do something similar or fix the patch on the FreeBSD
> kernel that you are working with. I am happy to help review and write
> patches but I don't work with the FreeBSD kernel so I wouldn't be able to
> help you quickly. However, I might have a suggestion. Do you know if
> FreeBSD can be booted by U-Boot ? Because U-Boot definitely boots as Xen on
> ARM guest firmware/bootloader. You should be able to build U-Boot and use
> the U-Boot binary as Xen guest kernel, then U-Boot could load FreeBSD from
> disk or network and start it. For instance as domU config file:
>
> kernel="/home/petalinux/u-boot.bin"
> disk = [ '/home/petalinux/test.img,raw,xvda' ]
>
> I know it is important to build u-boot with the following config to make
> it work on Xen.
>
> CONFIG_CMO_BY_VA_ONLY=y
>
>
>
> This option seems more doable to me according to my knowledge. But I need
> to understand how to do it.
>
> Well,let's say that on the ARM Chromebook I'm forced to use and install a
> customized version of u-boot,created by virtual open systems,because it is
> the only one that allows bypassing its bootloader protection. You can find
> more information here :
>
>
> http://www.virtualopensystems.com/en/solutions/guides/kvm-on-chromebook/?vos=tech
>
> This is the relevant section to read :
>
>
> Bootloader :
>
> If you wish to skip this chapter you can download a pre-compiled binary of
> the bootloader:
>
>
> $ wget
> http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/nv_u-boot-snow.kpart
>
>
> To be able to run KVM on ARM platforms, the kernel has to be booted in
> hypervisor mode. Because of this relatively recent requirement (due to the
> introduction of the virtualization extensions), up until now all booting
> methods would boot the kernel in the standard Supervisor mode. For the ARM
> Chromebook the default boot procedure doesn't allow us to boot in
> hypervisor mode. Although the laptop's boot mechanism is based on the
> frequently used u-boot, the binary is located in RO memory. Fortunately, a
> chained u-boot mechanism can be used (i.e. starting another u-boot after
> the original). We can then enter hypervisor mode from our custom iteration
> of u-boot and subsequently load our kernel and userspace.
>
> Checkout the needed u-boot code :
>
>
> $ git clone git://github.com/virtualopensystems/u-boot.git$ cd u-boot$
> ./scripts/build.sh
>
>
> If successful, a message about how to copy the bootloader on the USB flash
> disk or SD card will appear. We will use it later when preparing the boot
> medium to start our system. If you have followed the Setting up the boot
> medium chapter and you have a prepared boot device, then you can update
> u-boot by running :
>
>
> $ sudo dd if=nv_uboot-snow.kpart of=/dev/sdX1
>
>
>
> so,the needed u-boot that we must use should be installed on the first
> partition of the sd card.
>
> There is another relevant section to read :
>
>
> Setting up the boot medium
>
> Now it is time to copy all the relevant files that we created in the
> previous chapters,and use them to boot Chromebook with a different kernel
> and OS. In all these examples the device /dev/sdX is used. Take extra care
> to change the examples to the device that you have attached. Insert the
> boot medium on your workstation and carefully execute the following step.
> First we need to properly format the boot medium.
>
> In the uboot source directory :
>
>
> $ sudo ./scripts/sdcard.sh /dev/sdX
>
>
> This will erase all data and create 4 partitions in the medium, along with
> copying the u-boot binary to the first partition:
>
>
> Partition 1 = ChromeOS signed binary (V.O.S chained u-boot)
> Partition 2 = not used
> Partition 3 = EXT2 partition for u-boot files (uImage and
> exynos5250-snow.dtb)
> Partition 4 = EXT4 partition for userspace files
>
>
> With u-boot being copied, next is the kernel image and DTB file. From the
> kernel source execute :
>
>
> $ mkdir ../mnt/
> $ sudo mount /dev/sdX3 ../mnt/
> $ sudo cp arch/arm/boot/uImage ../mnt/
> $ sudo cp arch/arm/boot/dts/exynos5250-snow.dtb ../mnt/
> $ sudo umount /dev/sdX3
>
>
> Finally, we have to copy the Ubuntu userspace filesystem that we created
> earlier:
>
>
> $ sudo mount /dev/sdX4 mnt/$ sudo cp -a ./precise/* mnt/$ sudo umount
> /dev/sdX4
>
>
>
> Now,my idea is to chainload the already chain loaded u-boot created by
> V.O.S to the new u-boot that we need for booting FreeBSD and that can be
> installed in the partition n.2,as shown in this scheme,because it is not
> used :
>
>
> Partition 1 = ChromeOS signed binary (V.O.S chained u-boot)
> Partition 2 = not used (maybe we can install the u-boot for arm 32
> bit,compatible with FreeBSD on this partition)
> Partition 3 = EXT2 partition for u-boot files (uImage and
> exynos5250-snow.dtb)
> Partition 4 = EXT4 partition for userspace files
>
>
> Take in consideration that default boot string is hardcoded here,in the
> snow.h file of the custom u-boot created by VOS :
>
>
>
> https://github.com/virtualopensyste...18a39b6c177dff58a/include/configs/snow.h#L101
> <https://github.com/virtualopensystems/u-boot/blob/eecfeb578e296ef3b739ac918a39b6c177dff58a/include/configs/snow.h#L101>
>
>
> and it needs to be recompiled because it should point to the partition
> n.2,where I will install the u-boot files as explained here :
>
>
> https://wiki.freebsd.org/arm/Chromebook
>
>
> I have some questions to ask before I start working on this.
>
> 1) The xen developer said :
>
>
> You should be able to build U-Boot and use the U-Boot binary as Xen guest
> kernel...
>
>
>
> where is the u-boot binary,according to this document ?
>
> https://wiki.freebsd.org/arm/Chromebook
>
> I don't see it.
>
>
> 2) where is the source code of the file that I can get here :
>
>
> http://commondatastorage.googleapis.com/chromeos-localmirror/distfiles/nv_uboot-snow-simplefb.kpart.bz2
>
> I need the source code if I want to recompile u-boot so that it can point
> to the partition 4.
>
> Maybe it can be found on this link :
>
> http://linux-exynos.org/dist/chromebook/nv_uboot/
>
> but it can't be opened....
>
>
> 3) in this specific scenario the source code of u-boot should run on arm
> 32 bit,not on arm 64,because I have the Samsung Chromebook "SNOW" model
> XE303C12,that's powered by a Samsung Exynos 5250 (ARMv7 32 bit Cortex A15)
> Soc.
>
>
> 4) I'm not sure if I can chainload the customized u-boot created by V.O.S
> that should be installed on the first partition with the u-boot tailored
> for booting FreeBSD that should be installed on the partition 2....
>
>
> 5) the xen developer said that u-boot should be compiled enabling this
> option :
>
>
> Code:
>
> CONFIG_CMO_BY_VA_ONLY=y
>
>
>
> Well,can you provide some good source that can help me to understand how I
> can recompile u-boot for FreeBSD ? thanks.
>
> --
> Mario.
>
>

-- 
Mario.