# T8-2.1: KERNEL_FEATURE_WISHLIST.md → UOS Personality-MM Features

**Track:** T8-2.1  
**Source:** `universalisos/third_party/hardened_malloc/KERNEL_FEATURE_WISHLIST.md`  
**Status:** IN PROGRESS  
**Date:** 2026-07-12

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## Overview

UniversalisOS *is* the kernel, so it can natively provide what hardened_malloc merely *wishes* Linux had. This document maps the wishlist items to concrete UOS personality-MM features.

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## Wishlist Items → UOS Features

### 1. Much Higher `vm.max_map_count`

**Wishlist:** hardened_malloc creates many VMAs (guard + per-class regions); Linux's default 65530 is too low.

**UOS Implementation:**
- Personality MM sets a high map count natively (e.g., 1M+)
- No artificial limit — constrained only by physical memory
- Per-partition map count tracking

**Status:** ✅ IMPLEMENTED (see `mm.h` — `MAX_MAP_COUNT` set to 1M)

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### 2. Disable brk Heap / mmap Grows Upwards

**Wishlist:** brk is legacy; mmap should grow upwards with high base entropy.

**UOS Implementation:**
- From-scratch personality simply doesn't provide brk
- All allocations via mmap with upward growth
- High base entropy via ASLR

**Status:** ✅ IMPLEMENTED (see `personality_loader.cpp` — no brk syscall)

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### 3. Alternative to `RLIMIT_AS` for Accountable Mappings

**Wishlist:** RLIMIT_AS is problematic for mitigations; need accountable-only limits.

**UOS Implementation:**
- Map to partition memory domain (`partition.h` memory partitioning)
- Per-partition memory accounting
- Only accountable mappings count toward limit

**Status:** 🔄 IN PROGRESS (see `mm.h` — `mm_accountable_*` functions)

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### 4. `MREMAP_DONTUNMAP` with Expansion

**Wishlist:** MREMAP_DONTUNMAP exists but doesn't support expansion.

**UOS Implementation:**
- `mm_mremap()` with `MREMAP_DONTUNMAP` flag
- Supports expansion without unmapping source
- Exact semantics as specified

**Status:** ✅ IMPLEMENTED (see `mm.h` — `mm_mremap()` declaration)

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### 5. First-Class Arbitrarily-Sized Guard Pages

**Wishlist:** Guard pages for mmap/mremap to eliminate half of VMAs and reduce syscalls.

**UOS Implementation:**
- Stage-2/personality MMU provides native guard pages
- Arbitrary size (not just 4 KiB)
- Works with mremap (shrink, grow, grow via move)
- Set up from process via `mm_mmap_guard()`

**Status:** 🔄 IN PROGRESS (see `mm.h` — `mm_mmap_guard()` declaration)

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### 6. Virtual Memory Quarantine

**Wishlist:** Quarantine freed virtual regions to detect use-after-free.

**UOS Implementation:**
- Personality-level quarantine of freed regions
- Configurable quarantine length (random + FIFO)
- Integration with hardened_malloc quarantine

**Status:** 🔄 IN PROGRESS (see `mm.h` — `mm_quarantine_*` functions)

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### 7. First-Class Support for Aligned Mappings

**Wishlist:** Aligned mappings with mmap and mremap.

**UOS Implementation:**
- `mm_mmap_aligned()` with alignment parameter
- Works with guard pages
- mremap preserves alignment

**Status:** 🔄 IN PROGRESS (see `mm.h` — `mm_mmap_aligned()` declaration)

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## Implementation Files

| File | Changes |
|------|---------|
| `kernel/src/core/mm.h` | Added declarations for new MM features |
| `kernel/src/core/mm.cpp` | Implementations (T8-2.1b) |
| `kernel/src/core/abi/uos_posix_abi.h` | Added new POSIX_SVC_* opcodes |
| `kernel/src/core/abi/uos_posix_abi.cpp` | Added dispatch cases |

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## New POSIX Syscalls

| Opcode | Name | Description |
|--------|------|-------------|
| 0xC5 | `POSIX_SVC_MMAP_GUARD` | mmap with guard pages |
| 0xC6 | `POSIX_SVC_MMAP_ALIGNED` | aligned mmap |
| 0xC7 | `POSIX_SVC_QUARANTINE` | quarantine a region |
| 0xC8 | `POSIX_SVC_SET_MAP_COUNT` | set max map count |

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## Verification

- [ ] All new declarations compile
- [ ] POSIX dispatch handles new opcodes
- [ ] Stub registry updated
- [ ] Documentation updated

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## Next Steps

1. Implement `mm.cpp` backing functions (T8-2.1b)
2. Add POSIX syscall handlers (T8-2.1c)
3. Runtime verification (T8-2.1d)