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SUB-OS/kernel/main.c
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subhobhai943andClaude Opus 5 ecdc5be435 feat(exec): Run userland in ring 3 with an ELF64 loader and per-process page tables 
SUB-OS had a syscall table and user GDT descriptors but nothing that could
actually leave ring 0: lazybox and the shell run as kernel code, and
syscall_handler() was never reachable from a user program. This adds the
missing path end to end on x86_64.

Address spaces (arch/x86_64/mm/vmspace.c)
- The boot page tables identity-map the low 4 GB off PML4[0] and leave the
  rest empty, so userland is given its own PML4 slot (512 GiB) rather than
  holes punched in the kernel's 2 MB huge-page map. A process PML4 shares
  entry 0 with the kernel and privately owns entry 1.
- Frames outside the identity map are refused rather than written through an
  unmapped pointer; lifting that needs a recursive map or a higher-half
  direct map, which is noted in the file.

ELF loader (kernel/elf.c)
- Validates ELF64/little-endian/ET_EXEC/machine, bounds-checks every program
  header against both the image and the user address range, and lays PT_LOAD
  segments into an address space. Frames arrive zeroed, so .bss is covered.

Ring transition (arch/x86_64/cpu/usermode.asm)
- user_enter() drops to ring 3 via iretq after scrubbing every GPR, and
  user_return() unwinds back to it when the process exits, so exec looks like
  a call that blocks until the program finishes.

Syscalls
- INT 0x80 installed at DPL 3 with the Linux x86_64 register convention.
  The process gets its own kernel stack for the trap, because TSS.rsp0 must
  not point at the stack user_enter() is standing on.
- Every user pointer is range-checked before use. The process page tables are
  still live during a syscall, so without that check a program could pass a
  kernel address and have write(2) dump kernel text to the console. The new
  /sbin/init asserts both a wild pointer and a kernel pointer are rejected.
- write(2) to stdout/stderr routes through the new console_write(), which
  reuses printk's routing so output reaches serial and the framebuffer
  console rather than only the VGA text buffer.

Faults
- A ring 3 exception now kills that process and reports CR2 instead of
  panicking the machine.

Userland (userland/init/)
- /sbin/init is a real freestanding static executable, linked at the user
  base and embedded in the kernel image by scripts/mkblob.py. It reports its
  pid, verifies .bss was zeroed and .data is writable, checks the two pointer
  rejections, and exits.

aarch64 and armv8i keep building: the loader and exec path are portable, and
those ports get honest vmspace stubs that fail cleanly rather than pretending
to run a program with kernel privileges.

Verified under QEMU: init loads at 0x80004000a0, reports pid 1, .bss zeroed,
.data writable, both bad pointers rejected, and exits 0 back into the shell.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_0161Jh7uCEMLYEMNPsjC1LKf
2026-08-25 06:37:20 +00:00

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#include <kernel/kernel.h>
#include <kernel/printk.h>
#include <kernel/sched.h>
#include <kernel/task.h>
#include <kernel/signal.h>
#include <kernel/syscall.h>
#include <kernel/timer.h>
#include <kernel/workqueue.h>
#include <kernel/module.h>
#include <kernel/trace.h>
#include <kernel/namespace.h>
#include <kernel/syslog.h>
#include <kernel/cron.h>
#include <kernel/metrics.h>
#include <kernel/bpf.h>
#include <kernel/kobject.h>
#include <kernel/wait.h>
#include <kernel/futex.h>
#include <kernel/rcu.h>
#include <kernel/ktest.h>
#include <mm/page_cache.h>
#include <mm/vma.h>
#include <drivers/canvas.h>
#include <drivers/pty.h>
#include <arch/arch.h>
#include <mm/pmm.h>
#include <mm/kmalloc.h>
#include <mm/slab.h>
#include <drivers/tty.h>
#include <drivers/serial.h>
#include <drivers/keyboard.h>
#include <drivers/mouse.h>
#include <drivers/ata.h>
#include <drivers/ahci.h>
#include <drivers/nvme.h>
#include <drivers/bochs.h>
#include <drivers/virtio_blk.h>
#include <drivers/virtio_net.h>
#include <drivers/virtio_rng.h>
#include <drivers/hwmon.h>
#include <drivers/pci.h>
#include <drivers/e1000.h>
#include <drivers/rtl8139.h>
#include <drivers/speaker.h>
#include <drivers/fb.h>
#include <drivers/rtc.h>
#include <drivers/acpi.h>
#include <drivers/usb.h>
#include <drivers/xhci.h>
#include <drivers/ramdisk.h>
#include <block/block.h>
#include <ipc/ipc.h>
#include <sound/sound.h>
#include <sound/hda.h>
#include <sound/melody.h>
#include <fs/vfs.h>
#include <fs/fat32.h>
#include <fs/ext2.h>
#include <fs/sysfs.h>
#include <net/net.h>
#include <net/socket.h>
#include <net/udp.h>
#include <net/tcp.h>
#include <net/dhcp.h>
#include <net/dns.h>
#include <net/dns_cache.h>
#include <ipc/shm_posix.h>
#include <sound/beep.h>
#include <kernel/tsc.h>
#include <drivers/e1000e.h>
#include <drivers/virtio_gpu.h>
#include <drivers/cpufreq.h>
#include <drivers/virtio_input.h>
#include <kernel/rust.h>
#include <kernel/sub_lang.h>
#include <kernel/cpp_kernel.h>
#include <net/filter.h>
#include <net/http.h>
#include <net/ssh.h>
#include <crypto/crypto.h>
#include <certs/certs.h>
#include <security/security.h>
#include <security/auth.h>
#include <io_uring/io_uring.h>
#include <usr/initramfs.h>
#include <virt/virt.h>
#include <init/init.h>
#include <init/service.h>
#include <init/version.h>
#include <init/bootlogo.h>
#include <drivers/fbcon.h>
#include <userland/lazybox.h>
#include <userland/sh.h>
#include <userland/shell.h>
#include <kernel/exec.h>
static void subos_modular_core_boot(void) {
#if defined(__x86_64__)
pci_init();
#endif
// Storage & Block Layer
printk(KERN_INFO "[4/14] Initializing Block Layer & Storage Controllers... ");
block_init();
page_cache_init();
ramdisk_init();
#if defined(__x86_64__)
ata_init();
ahci_init();
nvme_init();
#endif
virtio_blk_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Bus & Devices
printk(KERN_INFO "[5/14] Enumerating System Devices, Canvas & PTY... ");
#if defined(__x86_64__)
virt_init();
fb_init();
bochs_vbe_init();
virtio_gpu_init();
usb_init();
xhci_init();
hwmon_init();
cpufreq_init();
#endif
canvas_init();
pty_init();
virtio_rng_init();
virtio_input_init();
tsc_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// The framebuffer exists from here on. This kernel boots to a text console,
// so the graphical splash is opt-in via `splash` on the command line --
// raising it by default would hide the very console we are about to use.
// The ASCII logo printed at the top of boot covers the default case.
if (init_has_param("splash") && !init_has_param("nosplash")) {
boot_logo_splash_begin();
} else {
// The adapter is in graphics mode from here on, so the VGA text buffer
// is no longer scanned out. Move the console to the framebuffer or the
// rest of the boot log is visible only on the serial line.
fbcon_enable(true);
}
// Network Subsystem, NetFilter, HTTPD & SSH Server
printk(KERN_INFO "[6/14] Initializing Network Stack, NetFilter, HTTPD & SSHD... ");
boot_logo_splash_progress(40, "Bringing up the network stack");
filter_init();
httpd_init();
sshd_init();
#if defined(__x86_64__)
rtl8139_init();
virtio_net_init();
e1000e_init();
if (e1000_init() || e1000e_is_online()) {
net_init();
socket_subsystem_init();
udp_init();
tcp_init();
dhcp_init();
dns_init();
dns_cache_init();
printk(ANSI_BRIGHT_GREEN "Online\n" ANSI_RESET);
} else {
printk(ANSI_YELLOW "No NIC detected\n" ANSI_RESET);
}
#else
virtio_net_init();
dns_cache_init();
printk(ANSI_BRIGHT_GREEN "Online\n" ANSI_RESET);
#endif
// Sound & Voice Synthesizer
#if defined(__x86_64__)
printk(KERN_INFO "[7/14] Initializing Sound Architecture, Melody Player & Formant TTS... ");
sound_init();
hda_init();
melody_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
#endif
// Crypto, Certificates, LSM Security, Authentication, Namespaces, Rust, SUB-Lang & C++ Subsystems
printk(KERN_INFO "[8/14] Initializing Rust, C++ Core, SUB-Lang Engine, Keyring & Auth... ");
boot_logo_splash_progress(55, "Starting Rust, C++ and SUB-Lang engines");
rust_kernel_init();
cpp_kernel_init();
sub_kernel_init();
prng_seed(0, 0);
certs_init();
security_init();
auth_init();
namespace_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Concurrency Primitives: Wait Queues, Futexes & Tiny RCU
printk(KERN_INFO "[9/14] Initializing Wait Queues, Futex Hash & Tiny RCU... ");
boot_logo_splash_progress(65, "Initializing concurrency primitives");
wait_subsystem_init();
futex_init();
rcu_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Inter-Process Communication
printk(KERN_INFO "[9/14] Initializing IPC Engine (Pipes, MsgQueues, POSIX SHM, Semaphores)... ");
ipc_init();
posix_shm_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Asynchronous I/O Engine
printk(KERN_INFO "[10/14] Initializing io_uring Async Ring Engine... ");
io_uring_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Virtual File System & Multi-Filesystem Support
printk(KERN_INFO "[11/14] Mounting Virtual File System (VFS, devfs, procfs, sysfs)... ");
boot_logo_splash_progress(78, "Mounting the virtual file system");
vfs_init();
sysfs_init();
kobject_subsystem_init();
fat32_init();
ext2_init();
initramfs_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Kernel Core: Signals, Modules, Syscalls, Tracing, Syslog, Metrics, Crond & Systemd
printk(KERN_INFO "[12/14] Initializing Syslog, Metrics, Cron, Tracing, BPF & Services... ");
boot_logo_splash_progress(88, "Starting kernel services");
signal_init();
workqueue_init();
syscall_init();
module_init_subsystem();
trace_init();
bpf_init();
syslog_init();
metrics_init();
cron_init();
service_manager_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Preemptive Multi-Tasking & Userland
printk(KERN_INFO "[13/14] Initializing Preemptive Task Scheduler & LazyBox... ");
boot_logo_splash_progress(95, "Starting the scheduler and userland");
sched_init();
lazybox_init();
ktest_init();
ktest_register_builtin_suites();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
// Hardware Interrupts
printk(KERN_INFO "[14/14] Enabling Hardware Interrupts... ");
arch_enable_interrupts();
printk(ANSI_BRIGHT_GREEN "ACTIVE\n" ANSI_RESET);
// Return the screen to the console before handing over to the shell.
boot_logo_splash_end();
fbcon_enable(true);
// Hand control to userland: /sbin/init is a separate static ELF that runs
// in ring 3 with its own page tables and talks back only through INT 0x80.
exec_run_builtin_init();
// Launch Shell
shell_run();
while (1) {
arch_halt();
}
}
#if defined(__x86_64__)
void kernel_main(void* memory_map, uint64_t memory_map_count) {
tty_init();
serial_init();
printk_init();
boot_logo_print_text();
printk(ANSI_BRIGHT_CYAN "=================================================================\n" ANSI_RESET);
printk(ANSI_BRIGHT_CYAN " SUB-OS 64-Bit [%s] Modular Monolithic Kernel %s\n" ANSI_RESET, arch_get_name(), kernel_get_version());
printk(ANSI_BRIGHT_CYAN "=================================================================\n\n" ANSI_RESET);
init_early("root=/dev/sda console=tty1 init=/bin/lazybox video=1280x720 quiet");
rtc_init();
printk(KERN_INFO "[1/14] Initializing 64-Bit GDT, IDT, PIC & PIT Timer... ");
arch_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
printk(KERN_INFO "[2/14] Initializing PS/2 Keyboard, Mouse & ACPI... ");
keyboard_init();
mouse_init();
acpi_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
printk(KERN_INFO "[3/14] Initializing Physical PMM, Dynamic Heap & SLAB Cache... ");
pmm_init(memory_map, memory_map_count);
heap_init();
slab_init();
vma_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
subos_modular_core_boot();
}
#elif defined(__aarch64__)
void kernel_main_aarch64(void) {
arch_early_init();
printk_init();
boot_logo_print_text();
printk(ANSI_BRIGHT_CYAN "=================================================================\n" ANSI_RESET);
printk(ANSI_BRIGHT_CYAN " SUB-OS 64-Bit [%s] Modular Monolithic Kernel %s\n" ANSI_RESET, arch_get_name(), kernel_get_version());
printk(ANSI_BRIGHT_CYAN "=================================================================\n\n" ANSI_RESET);
init_early("root=/dev/vda console=ttyAMA0 init=/bin/lazybox quiet");
printk(KERN_INFO "[1/14] Initializing AArch64 CPU, GICv2, Generic Timer & MMU... ");
arch_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
printk(KERN_INFO "[2/14] Initializing Physical PMM, Dynamic Heap & SLAB Cache... ");
pmm_init(NULL, 0);
heap_init();
slab_init();
vma_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
subos_modular_core_boot();
}
#elif defined(__arm__) || defined(__armv8i__)
void kernel_main_armv8i(void) {
arch_early_init();
printk_init();
printk(ANSI_BRIGHT_CYAN "=================================================================\n" ANSI_RESET);
printk(ANSI_BRIGHT_CYAN " SUB-OS 32-Bit [%s] Modular Monolithic Kernel %s\n" ANSI_RESET, arch_get_name(), kernel_get_version());
printk(ANSI_BRIGHT_CYAN "=================================================================\n\n" ANSI_RESET);
init_early("root=/dev/vda console=ttyAMA0 init=/bin/lazybox quiet");
printk(KERN_INFO "[1/14] Initializing ARMv8i CPU, GICv2, Generic Timer & MMU... ");
arch_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
printk(KERN_INFO "[2/14] Initializing Physical PMM, Dynamic Heap & SLAB Cache... ");
pmm_init(NULL, 0);
heap_init();
slab_init();
vma_init();
printk(ANSI_BRIGHT_GREEN "OK\n" ANSI_RESET);
subos_modular_core_boot();
}
#endif
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