Ciro Santilli @cirosantilli 37

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Aratu Week 2024 Talk by Ciro Santilli: My Best Random Projects / Everything is built from source and easily modifiable, powered by Buildroot  Updated 2025-06-17  +Created 2024-09-26

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The following are stored in submodules:

submodules/binutils-gdb/
submodules/buildroot/
submodules/gcc/
submodules/glibc/
submodules/linux/
submodules/qemu/

So you can modify source, rebuild and that's it, its in the VM.

E.g., let's hack the linux kernel:

asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
{
  pr_info("I'VE HACKED THE LINUX KERNEL!!!");

Rebuild Linux:

./build-linux

Rerun:

./run

And after boot we see:

<6>[    0.000000] I'VE HACKED THE LINUX KERNEL!!!

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Aratu Week 2024 Talk by Ciro Santilli: My Best Random Projects / Get a Linux terminal on QEMU  Updated 2025-06-17  +Created 2024-09-26

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One time setup:

git clone https://github.com/cirosantilli/linux-kernel-module-cheat
cd linux-kernel-module-cheat
sudo apt install docker
python3 -m venv .venv
. .venv/bin/activate
./setup
./run-docker create
./run-docker sh

You are now in Docker.

Build everything from source inside docker:

./build --download-dependencies qemu-buildroot

Boot Linux and get a userland shell:

./run

Outcome:

<6>[    1.383114] NET: Registered protocol family 17
<6>[    1.383682] 9pnet: Installing 9P2000 support
<6>[    1.385473] IPI shorthand broadcast: enabled
<6>[    1.385701] sched_clock: Marking stable (1355697980, 27047205)->(1385555667, -2810482)
<6>[    1.387744] ALSA device list:
<6>[    1.387843]   No soundcards found.
<6>[    1.535981] ata2.00: ATAPI: QEMU DVD-ROM, 2.5+, max UDMA/100
<5>[    1.543470] scsi 1:0:0:0: CD-ROM            QEMU     QEMU DVD-ROM     2.5+ PQ: 0 ANSI: 5
<6>[    1.548952] EXT4-fs (vda): mounting ext2 file system using the ext4 subsystem
<6>[    1.555909] EXT4-fs (vda): mounted filesystem without journal. Opts: (null)
<6>[    1.556145] VFS: Mounted root (ext2 filesystem) on device 254:0.
<6>[    1.557451] devtmpfs: mounted
<6>[    1.605639] Freeing unused kernel image (initmem) memory: 1248K
<6>[    1.605875] Write protecting the kernel read-only data: 16384k
<6>[    1.607977] Freeing unused kernel image (text/rodata gap) memory: 2044K
<6>[    1.610190] Freeing unused kernel image (rodata/data gap) memory: 1012K
<6>[    1.610495] Run /sbin/init as init process
<6>[    1.683311] tsc: Refined TSC clocksource calibration: 3293.671 MHz
<6>[    1.683618] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x2f79f177aae, max_idle_ns: 440795226653 ns
<6>[    1.683849] clocksource: Switched to clocksource tsc
<3>[    1.694241] 9pnet_virtio: no channels available for device host_data
mount: mounting host_data on /mnt/9p/data failed: No such file or directory
qemu-system-x86_64: warning: 9p: degraded performance: a reasonable high msize should be chosen on client/guest side (chosen msize is <= 8192). See https://wiki.qemu.org/Documentation/9pset.
<3>[    1.712287] overlayfs: overlapping upperdir path
mount: mounting overlay on /mnt/overlay failed: Too many levels of symbolic links
hello S98
hello .profile
/lkmc
root@buildroot# pwd
/lkmc
/lkmc
root@buildroot#

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