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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
99 lines
2.6 KiB
C
99 lines
2.6 KiB
C
#ifndef _KERNEL_ELF_H
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#define _KERNEL_ELF_H
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#include <stdint.h>
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#include <stddef.h>
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#include <mm/vmspace.h>
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/* ELF64 object file format, as far as a static executable needs it. */
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typedef uint64_t Elf64_Addr;
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typedef uint64_t Elf64_Off;
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typedef uint16_t Elf64_Half;
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typedef uint32_t Elf64_Word;
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typedef uint64_t Elf64_Xword;
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#define EI_NIDENT 16
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typedef struct {
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unsigned char e_ident[EI_NIDENT];
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Elf64_Half e_type;
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Elf64_Half e_machine;
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Elf64_Word e_version;
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Elf64_Addr e_entry;
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Elf64_Off e_phoff;
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Elf64_Off e_shoff;
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Elf64_Word e_flags;
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Elf64_Half e_ehsize;
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Elf64_Half e_phentsize;
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Elf64_Half e_phnum;
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Elf64_Half e_shentsize;
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Elf64_Half e_shnum;
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Elf64_Half e_shstrndx;
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} __attribute__((packed)) Elf64_Ehdr;
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typedef struct {
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Elf64_Word p_type;
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Elf64_Word p_flags;
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Elf64_Off p_offset;
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Elf64_Addr p_vaddr;
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Elf64_Addr p_paddr;
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Elf64_Xword p_filesz;
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Elf64_Xword p_memsz;
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Elf64_Xword p_align;
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} __attribute__((packed)) Elf64_Phdr;
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/* e_ident indices and values */
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#define EI_CLASS 4
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#define EI_DATA 5
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#define EI_VERSION 6
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#define ELFCLASS64 2
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#define ELFDATA2LSB 1
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#define EV_CURRENT 1
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/* e_type */
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#define ET_EXEC 2
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#define ET_DYN 3
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/* e_machine */
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#define EM_X86_64 62
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#define EM_AARCH64 183
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#define EM_ARM 40
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/* p_type */
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#define PT_NULL 0
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#define PT_LOAD 1
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#define PT_DYNAMIC 2
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#define PT_INTERP 3
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#define PT_NOTE 4
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#define PT_PHDR 6
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#define PT_GNU_STACK 0x6474e551
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/* p_flags */
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#define PF_X 0x1
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#define PF_W 0x2
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#define PF_R 0x4
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/* elf_load return codes */
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#define ELF_OK 0
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#define ELF_ETRUNCATED -1 /* image smaller than the headers claim */
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#define ELF_EMAGIC -2 /* not an ELF file */
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#define ELF_ECLASS -3 /* not ELF64 little-endian */
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#define ELF_ETYPE -4 /* not a static executable */
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#define ELF_EMACHINE -5 /* built for another architecture */
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#define ELF_ERANGE -6 /* a segment falls outside the user range */
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#define ELF_ENOMEM -7 /* out of physical pages */
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#define ELF_ENOENTRY -8 /* entry point is not inside any PT_LOAD */
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const char* elf_strerror(int err);
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/*
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* Parse a static ELF64 executable held in kernel memory and lay its PT_LOAD
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* segments into `vm`. On success *entry_out receives e_entry and *brk_out the
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* page-aligned end of the highest segment, which is where the heap starts.
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*/
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int elf_load(vmspace_t* vm, const void* image, size_t len,
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uint64_t* entry_out, uint64_t* brk_out);
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#endif /* _KERNEL_ELF_H */
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