Writing an x86 bootloader in Rust that can launch vmlinux

https://vmm.dev/en/rust/krabs.md

by lukastyrychtr • 6 years ago

148 52 6 years ago

vmm.dev

varbhat• 6 years ago

Looks nice.

I personally don't use Bootloaders anymore , using UEFI directly to boot my kernel.

Edit: It doesn't require any manual tinkering/maintainance even when updating. Also it boots fast.

https://wiki.archlinux.org/index.php/EFISTUB

bestouff• 6 years ago

How do you do that ? I didn't know you could compile a kernel directly to an UEFI payload.

Edit: Indeed it's possible with CONFIG_EFI_STUB=y : https://wiki.archlinux.org/index.php/EFISTUB - thanks for the hint !

mehrdadn4• 6 years ago

Note that just because you can, it doesn't mean you should. How much maintenance this needs depends on your distro, your machine and firmware's own quirks (if any), and your own usage/update/maintenance patterns/quirks.

alias_neo4• 6 years ago

Does that make kernel updates a more manual process? Are you building your own? Are you signing and using secure boot?

I'd be interested in giving this a try.

profsnuggles• 6 years ago

That is what I am doing as well. I'm building my own kernel but not using secure boot.

Kernel upgrades are just copying .config from the old kernel to the new kernel.

sudo make olddefconfig && sudo make && sudo make modules_install && install_kernel

The contents of install_kernel

KERNEL=`readlink /usr/src/linux`

NUMBER=${KERNEL##linux-}

NUMBER=${NUMBER%%-gentoo}

sudo cp arch/x86_64/boot/bzImage /boot/EFI/Gentoo/vmlinuz-${NUMBER}-gentoo.efi

sudo efi bootmgr -c -L "Gentoo ${NUMBER}" -l "\\EFI\\Gentoo\\vmlinuz-${NUMBER}-gentoo.efi" -d /dev/nvme0n1

josteink3• 6 years ago

Does that make kernel updates a more manual process? Are you building your own?

In Debian/Ubuntu it should be on by default, and has been for almost a decade:

https://askubuntu.com/questions/510009/does-the-ubuntu-kerne...

That means you can run your kernel directly as a UEFI-target and it will support secure-boot.

non-entity• 6 years ago

Is the site down right now? I can't seem to connect.

merricksb• 6 years ago

Must be swamped with traffic.

Google cache works:

https://webcache.googleusercontent.com/search?q=cache:QBPnre...

cpach• 6 years ago

That URL (to Google’s cached version) took about three minutes to load for me. Does anyone know why Google’s cache is so slow sometimes...?

stas2k• 6 years ago

Github repo has the same text in the README: https://github.com/o8vm/krabs

0x008• 6 years ago

Yes

secondcoming• 6 years ago

"Although the slice and the target buf should be the same, the target is filled with 255 from some point. "

Doesn't Rust prevent things like overwriting memory?

zaarn4• 6 years ago

Not necessarily, there are a bunch of unsafe methods you kinda have to use going this low level and if you're in unsafe mode, then you can overwrite memory or do things to corrupt it.

grayhatter• 6 years ago

So all all of rust's issues, and none of it's safety?

viraptor• 6 years ago

This is lower level than code you normally expect. The change seems to happen around switching addressing modes, so it could be something like pages descriptors not being set up correctly. In short - rust safe memory guarantees don't hold if you mess with memory mapping at runtime.

azhenley• 6 years ago

For those interested, a colleague of mine wrote a tutorial series on implementing an OS using Rust that targets RISC-V: https://osblog.stephenmarz.com/

m463• 6 years ago

I can't help but suspect the first item on the list was the whole reason for this project. :)

     Hardware initialization:

  ==>  Setting the keyboard repeat rate.
       Disable interrupts and mask all interrupt levels.
       Setting Interrupt descriptor (IDT) and segment descriptor (GDT). As a result,
       all selectors (CS, DS, ES, FS, GS) refer to the 4 Gbyte flat linear address space.
       Change the address bus to 32 bits (Enable A20 line).
       Transition to protected mode.
       If the target is ELF64, set the 4G boot pagetable and transition to long mode.

Writing an x86 bootloader in Rust that can launch vmlinux

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