QEMU Linux Kernel Panic With BusyBox - linux

Question

I am following this guide to run a minimal linux kernel on top of QEMU, and keep running into the same issue. I have also tried other similar tutorials and end up with the same panic. Since the panic seems to be related to the /init script, I have tried swapping this out with a (statically linked) binary but still end up with the panic. The only thing I have done differently from the tutorial is using the latest stable version of BusyBox (currently 1.34.1). The text of the panic is here and linked below. If anyone has any insight on this that would be great!
Linux version 5.15.0+ (michael#tree) (gcc (Gentoo Hardened 10.3.0-r2 p3) 10.3.0, GNU ld (G1
Command line: console=ttyS0
x86/fpu: x87 FPU will use FXSAVE
signal: max sigframe size: 1040
BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x0000000007fdffff] usable
BIOS-e820: [mem 0x0000000007fe0000-0x0000000007ffffff] reserved
BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
NX (Execute Disable) protection: active
SMBIOS 2.8 present.
DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS d55cb5a 04/01/2014
tsc: Fast TSC calibration using PIT
tsc: Detected 3992.482 MHz processor
last_pfn = 0x7fe0 max_arch_pfn = 0x400000000
x86/PAT: Configuration [0-7]: WB WC UC- UC WB WP UC- WT
found SMP MP-table at [mem 0x000f5c80-0x000f5c8f]
RAMDISK: [mem 0x07cf6000-0x07fdffff]
Zone ranges:
DMA [mem 0x0000000000001000-0x0000000000ffffff]
DMA32 [mem 0x0000000001000000-0x0000000007fdffff]
Normal empty
Movable zone start for each node
Early memory node ranges
node 0: [mem 0x0000000000001000-0x000000000009efff]
node 0: [mem 0x0000000000100000-0x0000000007fdffff]
Initmem setup node 0 [mem 0x0000000000001000-0x0000000007fdffff]
On node 0, zone DMA: 1 pages in unavailable ranges
On node 0, zone DMA: 97 pages in unavailable ranges
On node 0, zone DMA32: 32 pages in unavailable ranges
Intel MultiProcessor Specification v1.4
MPTABLE: OEM ID: BOCHSCPU
MPTABLE: Product ID: 0.1
MPTABLE: APIC at: 0xFEE00000
Processor #0 (Bootup-CPU)
IOAPIC[0]: apic_id 0, version 32, address 0xfec00000, GSI 0-23
Processors: 1
[mem 0x08000000-0xfffbffff] available for PCI devices
clocksource: refined-jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 764551s
Built 1 zonelists, mobility grouping on. Total pages: 31968
Kernel command line: console=ttyS0
Dentry cache hash table entries: 16384 (order: 5, 131072 bytes, linear)
Inode-cache hash table entries: 8192 (order: 4, 65536 bytes, linear)
mem auto-init: stack:off, heap alloc:off, heap free:off
Memory: 114084K/130552K available (4097K kernel code, 768K rwdata, 484K rodata, 532K init,)
SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
NR_IRQS: 4352, nr_irqs: 48, preallocated irqs: 16
Console: colour VGA+ 80x25
printk: console [ttyS0] enabled
APIC: Switch to symmetric I/O mode setup
..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
clocksource: tsc-early: mask: 0xffffffffffffffff max_cycles: 0x73193cf9da3, max_idle_ns: 8s
Calibrating delay loop (skipped), value calculated using timer frequency.. 7984.96 BogoMIP)
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
Mountpoint-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0, 1GB 0
CPU: AMD QEMU Virtual CPU version 2.5+ (family: 0x6, model: 0x6, stepping: 0x3)
Spectre V1 : Mitigation: usercopy/swapgs barriers and __user pointer sanitization
Spectre V2 : Spectre mitigation: kernel not compiled with retpoline; no mitigation availab!
Speculative Store Bypass: Vulnerable
Performance Events: PMU not available due to virtualization, using software events only.
clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 76450417851000s
futex hash table entries: 256 (order: 0, 6144 bytes, linear)
clocksource: Switched to clocksource tsc-early
platform rtc_cmos: registered platform RTC device (no PNP device found)
Unpacking initramfs...
workingset: timestamp_bits=62 max_order=15 bucket_order=0
Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
serial8250: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
random: get_random_bytes called from init_oops_id+0x2f/0x40 with crng_init=0
sched_clock: Marking stable (333996480, 16836404)->(354705829, -3872945)
Freeing initrd memory: 2984K
Freeing unused kernel image (initmem) memory: 532K
Write protecting the kernel read-only data: 8192k
Freeing unused kernel image (text/rodata gap) memory: 2044K
Freeing unused kernel image (rodata/data gap) memory: 1564K
Run /init as init process
Failed to execute /init (error -13)
Run /sbin/init as init process
Run /etc/init as init process
Run /bin/init as init process
Run /bin/sh as init process
Kernel panic - not syncing: No working init found. Try passing init= option to kernel. Se.
CPU: 0 PID: 1 Comm: swapper Not tainted 5.15.0+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS d55cb5a 04/01/2014
Call Trace:
<TASK>
dump_stack+0x20/0x22
panic+0xd0/0x246
? rest_init+0x90/0x90
kernel_init+0xfc/0x100
ret_from_fork+0x1f/0x30
</TASK>
Kernel Offset: disabled
---[ end Kernel panic - not syncing: No working init found. Try passing init= option to k-
QEMU 6.0.0 monitor - type 'help' for more information
(qemu) quit
Additionally, I have actually tried very similar steps on a completely different computer, so I'm pretty sure there is something I am missing in-general. Both machines are running Gentoo but I have successfully used QEMU to emulate other existing operating systems on both devices (so I think I can exclude a missing kernel configuration)?

Answer 1

Add execute mode to /init file before you build CPIO initramfs:
chmod +x <path-to-your-initrd-root>/init