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subhobhai943andClaude Opus 5
ecdc5be435
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
67 lines
1.7 KiB
Python
Executable File
67 lines
1.7 KiB
Python
Executable File
#!/usr/bin/env python3
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"""Embed a binary file into the kernel image as a C byte array.
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Used by the build to carry the statically linked /sbin/init ELF inside the
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kernel, so the ELF loader has something to run before any filesystem is
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mounted.
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usage: mkblob.py <input-binary> <output.c> <symbol-name>
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"""
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import os
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import sys
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def main():
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if len(sys.argv) != 4:
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sys.stderr.write(f"usage: {os.path.basename(sys.argv[0])} "
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"<input-binary> <output.c> <symbol-name>\n")
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return 2
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src, dst, symbol = sys.argv[1], sys.argv[2], sys.argv[3]
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try:
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with open(src, "rb") as handle:
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payload = handle.read()
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except OSError as exc:
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sys.stderr.write(f"mkblob: cannot read {src}: {exc}\n")
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return 1
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if not payload:
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sys.stderr.write(f"mkblob: {src} is empty\n")
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return 1
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out = [
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"/* Automatically generated by scripts/mkblob.py. Do not edit. */",
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f'/* source: {os.path.basename(src)} ({len(payload)} bytes) */',
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"",
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"#include <stddef.h>",
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"",
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f"const unsigned char {symbol}[] = {{",
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]
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for offset in range(0, len(payload), 12):
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chunk = payload[offset:offset + 12]
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out.append(" " + " ".join(f"0x{b:02x}," for b in chunk))
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out += [
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"};",
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"",
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f"const size_t {symbol}_len = sizeof({symbol});",
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"",
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]
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os.makedirs(os.path.dirname(os.path.abspath(dst)), exist_ok=True)
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try:
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with open(dst, "w") as handle:
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handle.write("\n".join(out))
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except OSError as exc:
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sys.stderr.write(f"mkblob: cannot write {dst}: {exc}\n")
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return 1
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return 0
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if __name__ == "__main__":
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sys.exit(main())
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