RedBear-OS/local/docs/KERNEL-IPC-CREDENTIAL-PLAN.md

Red Bear OS — Kernel, IPC, and Credential Syscalls Plan

Date: 2026-04-30 Scope: Kernel architecture, IPC infrastructure, credential syscalls, process isolation Implementation status: Phases K1-K2, K4 ✅ complete. Phases K3, K5 deferred. Status: This document is the canonical kernel + IPC plan, extending local/docs/COMPREHENSIVE-OS-ASSESSMENT.md

1. Purpose

This plan defines the implementation roadmap for kernel hardening, IPC improvements, and credential syscall implementation in Red Bear OS. It is the canonical kernel authority superseding scattered kernel guidance in other docs.

Relationship to existing plans:

Document	Relationship
CONSOLE-TO-KDE-DESKTOP-PLAN.md	Parent: CONSOLE-TO-KDE v4.0 (Kernel & Core Infrastructure)
IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md	Sibling: IRQ/PCI/MSI-X — not duplicated here
RELIBC-IPC-ASSESSMENT-AND-IMPROVEMENT-PLAN.md	Companion: relibc IPC surface — this plan covers kernel side
ACPI-IMPROVEMENT-PLAN.md	Sibling: ACPI power/shutdown — relevant for §4 (shutdown robustness)
CONSOLE-TO-KDE-DESKTOP-PLAN.md	Consumer: desktop stack depends on kernel work here

2. Current Architecture Assessment

2.1 Kernel Overview

The Redox microkernel (recipes/core/kernel/source/) is a ~20-40k LoC Rust microkernel. It runs in ring 0 and provides:

• 12 kernel schemes: debug, event, memory, pipe, irq, time, sys, proc, serio, acpi, dtb, user (userspace scheme wrapper)
• ~35 handled syscalls: file I/O, memory mapping, process control, futex, time
• Catch-all ENOSYS: all unhandled syscall numbers return ENOSYS

recipes/core/kernel/source/src/
├── syscall/           # Syscall dispatch: mod.rs (handlers), fs.rs, process.rs, futex.rs, time.rs
│   └── mod.rs         # Main syscall() dispatch: 35 explicit match arms, _ => ENOSYS
├── scheme/            # Kernel schemes: debug, event, memory, pipe, irq, time, sys, proc, serio
│   ├── mod.rs         # Scheme trait definition, SchemeId, FileHandle types
│   ├── proc.rs        # Process manager scheme (fork, exec, signal, credential setting)
│   └── sys/           # System info scheme: context list, syscall debug, uname
├── context/           # Process/thread context management
│   ├── context.rs     # Context struct: euid, egid, pid, files, signals, addr_space
│   └── memory.rs      # Address space, grants, mmap implementation
├── memory/            # Physical/virtual memory management, page tables
└── sync/              # Locking primitives (RwLock, Mutex, CleanLockToken)

2.2 Syscall Dispatch Architecture

The kernel's syscall() function in syscall/mod.rs dispatches based on a (syscall number):

// From recipes/core/kernel/source/src/syscall/mod.rs (line 75)
match a {
    SYS_WRITE2 => file_op_generic_ext(..),
    SYS_WRITE  => sys_write(..),
    SYS_FMAP   => { .. },           // Anonymous or file-backed mmap
    SYS_READ2  => file_op_generic_ext(..),
    SYS_READ   => sys_read(..),
    SYS_FPATH  => file_op_generic(..),
    SYS_FSTAT  => fstat(..),
    SYS_DUP    => dup(..),
    SYS_DUP2   => dup2(..),
    SYS_SENDFD => sendfd(..),
    SYS_OPENAT => openat(..),
    SYS_UNLINKAT => unlinkat(..),
    SYS_CLOSE  => close(..),
    SYS_CALL   => call(..),         // Scheme IPC: send message to scheme
    SYS_FEVENT => fevent(..),       // Register event on fd
    SYS_YIELD  => sched_yield(..),
    SYS_NANOSLEEP => nanosleep(..),
    SYS_CLOCK_GETTIME => clock_gettime(..),
    SYS_FUTEX  => futex(..),
    SYS_MPROTECT => mprotect(..),
    SYS_MREMAP => mremap(..),
    // ... ~15 more file operations (fchmod, fchown, fcntl, flink, frename, ftruncate, fsync, etc.)
    _ => Err(Error::new(ENOSYS)),   // ← CATCH-ALL: all credential syscalls fall here
}

Syscall numbers come from the external redox_syscall crate (crates.io), not from the kernel tree. The kernel consumes them via use syscall::number::*.

2.3 Credential Architecture (Current)

Kernel Context struct (context/context.rs):

pub struct Context {
    // Credential fields (initialized to 0):
    pub euid: u32,      // Effective user ID — used for scheme access control
    pub egid: u32,      // Effective group ID
    pub pid: usize,     // Process ID (set via proc scheme)

    // NOT present in kernel:
    //   ruid, suid     — real/saved UID (maintained in userspace redox-rt)
    //   rgid, sgid     — real/saved GID (maintained in userspace redox-rt)
    //   supplementary groups — not implemented anywhere

    // Access control interface:
    pub fn caller_ctx(&self) -> CallerCtx {
        CallerCtx { uid: self.euid, gid: self.egid, pid: self.pid }
    }
}

Credential read path (userspace, no kernel involvement):

getuid() → relibc::platform::redox::getuid()
  → redox_rt::sys::posix_getresugid()
    → reads local DYNAMIC_PROC_INFO { ruid, euid, suid, rgid, egid, sgid }
    → returns cached userspace values (NO kernel syscall)

Credential write path (through proc: scheme):

setresuid(ruid, euid, suid) → relibc::platform::redox::setresuid()
  → redox_rt::sys::posix_setresugid(&Resugid { ruid, euid, suid, .. })
    → packs 6×u32 into buffer
    → this_proc_call(&buf, CallFlags::empty(), &[ProcCall::SetResugid as u64])
      → SYS_CALL to proc: scheme
        → kernel proc scheme handler (scheme/proc.rs:1269):
            guard.euid = info.euid;
            guard.egid = info.egid;

Key finding: The kernel DOES support credential setting through the proc: scheme, using ProcSchemeAttrs with euid/egid/pid/prio/debug_name fields. The getuid()/getgid() functions work through userspace-cached values in redox-rt. setresuid()/setresgid() work through the proc scheme.

What's genuinely broken:

Function	Status	Root Cause
setgroups()	ENOSYS stub	relibc/redox/mod.rs:1205 — todo_skip!(0, "setgroups({}, {:p}): not implemented")
getgroups()	/etc/group-based	Works via getpwuid() + getgrent() iteration — doesn't use kernel groups
initgroups()	No-op	No supplementary group infrastructure

2.4 IPC Architecture

Scheme-based IPC is the primary IPC mechanism:

┌─────────────┐     SYS_CALL(syscall)      ┌──────────────┐
│  Userspace   │ ──────────────────────────→│   Kernel      │
│  Process A   │   open/read/write/fevent   │   Scheme      │
│              │ ←──────────────────────────│   Dispatch    │
└─────────────┘     result (usize/-errno)   └──────┬───────┘
                                                    │
                              ┌─────────────────────┤
                              │                     │
                         ┌────▼──────┐       ┌──────▼──────┐
                         │  Kernel    │       │  Userspace   │
                         │  Schemes   │       │  Scheme      │
                         │  (12)      │       │  Daemons     │
                         │            │       │  (via user:) │
                         │ debug:     │       │              │
                         │ event:     │       │ ptyd         │
                         │ memory:    │       │ pcid         │
                         │ pipe:      │       │ ext4d        │
                         │ irq:       │       │ fatd         │
                         │ time:      │       │ redox-drm    │
                         │ sys:       │       │ ...          │
                         │ proc:      │       │              │
                         │ serio:     │       │              │
                         └───────────┘       └──────────────┘

IPC primitives available:

Primitive	Mechanism	Kernel/Userspace
pipe: scheme	Kernel pipe scheme — bidirectional byte streams	Kernel
shm_open() / mmap(MAP_SHARED)	Shared memory via memory scheme grants	Kernel
SYS_CALL + scheme messages	Send/receive typed messages to scheme daemons	Kernel dispatch, userspace handler
fevent()	Register kernel-level events on file descriptors	Kernel
sendfd()	Pass file descriptors between processes	Kernel
event: scheme	Kernel event notification (used by eventfd/signalfd/timerfd)	Kernel
Signals	sigprocmask + sigaction via proc: scheme	Kernel delivery, userspace handling
Futex	Fast userspace mutex via SYS_FUTEX	Kernel

Current IPC limitations:

Limitation	Impact
No SYS_PTRACE	ptrace not available (handled via proc: scheme paths)
No SYS_KILL	Signal sending via proc: scheme only
eventfd/signalfd/timerfd recipe-applied	Bounded compatibility layers, not plain-source
ifaddrs synthetic	Only loopback + eth0, not live enumeration
POSIX message queues not implemented	mqueue.h missing entirely
SysV message queues not implemented	sys/msg.h missing entirely
No UNIX domain sockets (AF_UNIX) path	Socket-based IPC limited

2.5 Process Model

Redox uses a userspace process manager (procmgr via proc: scheme):

• fork: Implemented through proc: scheme → kernel creates new Context with cloned address space
• exec: Replaces address space with new executable image
• spawn: Combined fork+exec via proc: scheme
• wait/waitpid/waitid: Recipe-applied patch via proc: scheme (signals child exit)
• Credentials on fork: Address space cloned (userspace DYNAMIC_PROC_INFO inherited)
• Credentials on exec: setresuid() behavior (suid-bit not implemented in kernel)

The kernel's Context struct tracks:

• owner_proc_id: Option<NonZeroUsize> — parent process for exit notification
• files: Arc<LockedFdTbl> — file descriptor table (can be shared)
• addr_space: Option<Arc<AddrSpaceWrapper>> — address space (can be shared = threads)
• sig: Option<SignalState> — signal handler configuration

3. Critical Gaps and Blockers

3.1 Credential Syscall Blocker (Priority: P0-CRITICAL)

The setgroups() function is ENOSYS. This blocks:

• polkit — uses setgroups() for privilege management
• dbus-daemon — uses credentials for service activation
• logind / redbear-sessiond — needs credential awareness
• sudo / su — uses initgroups() → setgroups()
• Any program that changes user identity

Root cause chain:

1. redox_syscall crate (crates.io, upstream) has no SYS_SETGROUPS/SYS_GETGROUPS numbers
2. Kernel has no supplementary group table in Context struct
3. No group inheritance on fork/exec
4. relibc setgroups() is a todo_skip!() stub
5. getgroups() bypasses kernel entirely (reads /etc/group)

3.2 Kernel-Level Access Control Gap (Priority: P1)

The kernel's caller_ctx() provides {euid, egid, pid} to scheme handlers, but:

1. No consistent enforcement: Kernel schemes may or may not check caller credentials
2. No ruid/suid tracking: Cannot distinguish real vs effective identity in kernel
3. All processes start as root (euid=0, egid=0): No privilege separation at boot
4. No supplementary groups in kernel: Only egid checked

3.3 IPC Completeness Gaps (Priority: P2)

Gap	Priority	Blocked By
POSIX message queues (mqueue.h)	P2	Scheme design needed
SysV message queues (sys/msg.h)	P2	Scheme design needed
UNIX domain sockets (AF_UNIX)	P2	Kernel or scheme implementation
Non-synthetic ifaddrs	P3	Network stack enumeration
eventfd/signalfd/timerfd → plain-source	P3	Upstream relibc convergence

3.4 Resource Limits (Priority: P2)

SYS_GETRLIMIT / SYS_SETRLIMIT return ENOSYS. This is a microkernel design choice:

• Resource limits are typically library-level policy in capability systems
• Current approach: limits enforced in userspace daemons
• Desktop impact: systemd/logind expect rlimit support for service management

3.5 Shutdown Robustness (Priority: P2)

ACPI shutdown via kstop eventing exists but has gaps:

• acpid startup has panic-grade expect paths
• _S5 derivation gated on PCI timing
• DMAR orphaned in acpid source
• See local/docs/ACPI-IMPROVEMENT-PLAN.md for full detail

4. Implementation Plan

Phase K1: Kernel Credential Foundation (Week 1-2)

Goal: Add supplementary group support to the kernel and wire setgroups()/getgroups().

K1.1 — Add supplementary groups to kernel Context

// Context struct additions (context/context.rs):
pub struct Context {
    // Existing:
    pub euid: u32,
    pub egid: u32,
    pub pid: usize,

    // NEW: Real/saved IDs (moved from userspace redox-rt to kernel):
    pub ruid: u32,
    pub rgid: u32,
    pub suid: u32,
    pub sgid: u32,

    // NEW: Supplementary groups
    pub groups: Vec<u32>,  // Or Arc<[u32]> for sharing
}

Files modified:

• recipes/core/kernel/source/src/context/context.rs — add fields, initialize, clone on fork
• recipes/core/kernel/source/src/scheme/proc.rs — extend ProcSchemeAttrs to include ruid/suid/rgid/sgid/groups
• local/patches/kernel/ — new patch: P4-credential-fields.patch

K1.2 — Add SYS_SETGROUPS and SYS_GETGROUPS to redox_syscall

The redox_syscall crate is upstream (crates.io). Red Bear must either:

• Option A (preferred): Contribute upstream PR to add syscall numbers
• Option B: Vendor fork of redox_syscall in local/ overlay
• Option C: Define Red Bear-local syscall numbers in kernel directly

Recommended: Option A + B fallback:

1. Submit upstream PR to redox_syscall adding:

   • SYS_SETGROUPS, SYS_GETGROUPS
   • SYS_SETUID, SYS_SETGID, SYS_GETUID, SYS_GETGID
   • SYS_GETEUID, SYS_GETEGID
   • SYS_SETREUID, SYS_SETREGID
   • SYS_GETRESUID, SYS_GETRESGID

2. While upstream PR is pending, use a local redox_syscall patch:

   • Copy redox_syscall crate into local/vendor/redox_syscall/
   • Add syscall number constants
   • Point kernel Cargo.toml to local path
   • Patch tracked in local/patches/kernel/P4-redox-syscall-numbers.patch

K1.3 — Add kernel syscall handlers

New file: recipes/core/kernel/source/src/syscall/cred.rs

// Credential syscall handlers
pub fn setresuid(ruid: u32, euid: u32, suid: u32, token: &mut CleanLockToken) -> Result<usize> {
    let context_lock = context::current();
    let mut context = context_lock.write(token.token());

    // Permission check: must be root or match current values
    if context.euid != 0 {
        if let Some(ruid) = ruid_opt { /* check ruid == current ruid/euid/suid */ }
        // ... POSIX permission model
    }

    // Set values
    if ruid != u32::MAX { context.ruid = ruid; }
    if euid != u32::MAX { context.euid = euid; }
    if suid != u32::MAX { context.suid = suid; }
    Ok(0)
}

pub fn setgroups(groups: &[u32], token: &mut CleanLockToken) -> Result<usize> {
    // Requires: euid == 0
    let context_lock = context::current();
    let mut context = context_lock.write(token.token());
    if context.euid != 0 { return Err(Error::new(EPERM)); }
    context.groups = groups.to_vec();
    Ok(0)
}

pub fn getgroups(token: &mut CleanLockToken) -> Result<Vec<u32>> {
    let context_lock = context::current();
    let context = context_lock.read(token.token());
    Ok(context.groups.clone())
}

Modified file: recipes/core/kernel/source/src/syscall/mod.rs

match a {
    // ... existing arms ...
    SYS_SETRESUID => setresuid(b as u32, c as u32, d as u32, token),
    SYS_SETRESGID => setresgid(b as u32, c as u32, d as u32, token),
    SYS_GETRESUID => getresuid(UserSlice::wo(b, c)?, token),
    SYS_GETRESGID => getresgid(UserSlice::wo(b, c)?, token),
    SYS_SETUID   => setuid(b as u32, token),
    SYS_SETGID   => setgid(b as u32, token),
    SYS_GETUID   => Ok(getuid(token)),
    SYS_GETGID   => Ok(getgid(token)),
    SYS_GETEUID  => Ok(geteuid(token)),
    SYS_GETEGID  => Ok(getegid(token)),
    SYS_SETGROUPS => setgroups(UserSlice::ro(b, c)?, token).map(|()| 0),
    SYS_GETGROUPS => getgroups(UserSlice::wo(b, c)?, token),
    // ... existing arms ...
}

K1.4 — Wire relibc setgroups()/getgroups() through real syscalls

Modified: recipes/core/relibc/source/src/platform/redox/mod.rs

// Replace todo_skip!() stub:
unsafe fn setgroups(size: size_t, list: *const gid_t) -> Result<()> {
    if size < 0 || size > NGROUPS_MAX { return Err(Errno(EINVAL)); }
    let groups = core::slice::from_raw_parts(list, size as usize);
    syscall::setgroups(groups)?;
    Ok(())
}

// Replace /etc/group-based getgroups:
fn getgroups(mut list: Out<[gid_t]>) -> Result<c_int> {
    let mut buf = [0u32; NGROUPS_MAX as usize];
    let count = syscall::getgroups(&mut buf)?;
    for (i, gid) in buf[..count].iter().enumerate() {
        list[i] = *gid as gid_t;
    }
    Ok(count as c_int)
}

K1.5 — Add credential syscall stubs in redox-rt

Modified: recipes/core/relibc/source/redox-rt/src/sys.rs

pub fn setgroups(groups: &[u32]) -> Result<()> {
    unsafe {
        redox_syscall::syscall5(
            redox_syscall::SYS_SETGROUPS,
            groups.as_ptr() as usize,
            groups.len(),
            0, 0, 0,
        )
        .map(|_| ())
        .map_err(|e| Error::new(e.errno as i32))
    }
}

pub fn getgroups(buf: &mut [u32]) -> Result<usize> {
    unsafe {
        redox_syscall::syscall3(
            redox_syscall::SYS_GETGROUPS,
            buf.as_mut_ptr() as usize,
            buf.len(),
            0,
        )
        .map_err(|e| Error::new(e.errno as i32))
    }
}

K1.6 — Patch management

All kernel and relibc source changes must be mirrored into local/patches/:

local/patches/
├── kernel/
│   ├── redox.patch                    # Updated symlink target
│   ├── P4-credential-fields.patch     # Context struct additions
│   ├── P4-credential-syscalls.patch   # Syscall handlers + dispatch
│   └── P4-redox-syscall-numbers.patch # Local redox_syscall additions
├── relibc/
│   ├── P4-setgroups-kernel.patch      # Setgroups through real syscall
│   ├── P4-getgroups-kernel.patch      # Getgroups through real syscall
│   └── P4-redox-rt-cred-syscalls.patch # redox-rt syscall wrappers

Phase K2: Kernel Access Control Hardening (Week 2-3)

Goal: Enforce credential checks in kernel schemes, add proper privilege separation.

K2.1 — Enforce scheme-level credential checks

Each kernel scheme handler currently receives CallerCtx { uid, gid, pid }. Ensure consistent credential enforcement:

Scheme	Current Check	Required Check
memory:	Physical memory access → root only	✅ Already enforced (euid==0 for phys)
irq:	IRQ registration → root only	✅ Already enforced
proc:	Process inspection → caller == target OR root	🔄 Review: ensure consistent
sys:	System info → read-only for all	✅ Appropriate
debug:	Debug output → should be root-only	🔄 Review: add check
serio:	PS/2 device → root only	🔄 Review: add check
event:	Event registration → process-own only	🔄 Review: ensure isolation

K2.2 — Bootstrap with non-root init process

Currently all processes start as euid=0/egid=0. The boot sequence should:

1. Kernel bootstrap context starts as root (euid=0, egid=0) — required for init
2. Init (/sbin/init) runs as root
3. Init drops privileges before spawning user services:

   // In init or service manager:
   setresuid(1000, 1000, 1000);  // Drop to regular user
   setgroups(&[1000, 27, 100]);  // Set supplementary groups
   // Then spawn child services with restricted permissions
   

K2.3 — Add initgroups() support

// In relibc/src/platform/redox/mod.rs:
fn initgroups(user: CStr, group: gid_t) -> Result<()> {
    // 1. Set primary group
    setgid(group)?;
    // 2. Parse /etc/group for supplementary groups containing this user
    let mut groups = vec![group];
    // ... iterate getgrent() to find user memberships ...
    // 3. Set supplementary groups via kernel syscall
    setgroups(&groups)?;
    Ok(())
}

Phase K3: IPC Infrastructure Improvements (Week 3-5)

Goal: Complete IPC primitives needed for desktop infrastructure.

K3.1 — POSIX Message Queues (mqueue.h)

Design decision: Implement as a userspace scheme daemon (not kernel syscalls).

mqd:
├── Registers as scheme:mqueue
├── Stores queues in memory backed by shm_open() + mmap()
├── mq_open() → open scheme:mqueue/{name}
├── mq_send() → write to fd
├── mq_receive() → read from fd
├── mq_notify() → fevent() on fd for async notification
├── mq_close() → close fd
└── mq_unlink() → unlink scheme:mqueue/{name}

Implementation:

• New Red Bear package: local/recipes/system/mqueued/
• Relibc header: recipes/core/relibc/source/src/header/mqueue/
• Recipe in local/recipes/system/mqueued/recipe.toml
• Init service: /usr/lib/init.d/50_mqueued.service

K3.2 — SysV Message Queues (sys/msg.h)

Design decision: Implement as scheme daemon or on top of POSIX message queues.

• Recommended: implement directly alongside mqueued using shared infrastructure.
• Low priority — Qt/KDE do not depend on SysV msg queues.

K3.3 — UNIX Domain Sockets (AF_UNIX / SOCK_STREAM)

Current state: D-Bus uses abstract sockets on Linux. Redox uses scheme-based communication.

• For D-Bus compatibility: redbear-sessiond already uses zbus with custom transport
• For general AF_UNIX: implement as scheme:unix daemon backed by kernel pipe scheme
• Priority: P3 — D-Bus is already working through scheme transport

K3.4 — Non-synthetic Interface Enumeration

Replace the hardcoded loopback + eth0 model with live network interface enumeration:

• Query smolnetd or equivalent for active interfaces
• Expose through getifaddrs() properly
• Priority: P3 — needed for NetworkManager-like functionality

K3.5 — eventfd/signalfd/timerfd → plain-source convergence

Current state: all three are recipe-applied patches. Goal: upstream into relibc mainline.

• Monitor upstream relibc for equivalent implementations
• When upstream absorbs: shrink/drop Red Bear patch chain
• When upstream does NOT absorb after 3+ months: promote to durable Red Bear-maintained
• See local/docs/RELIBC-IPC-ASSESSMENT-AND-IMPROVEMENT-PLAN.md Phase I5

Phase K4: Resource Limits and Process Management (Week 4-6)

K4.1 — RLIMIT Support

Decision: Enforce resource limits in userspace, not kernel.

• The kernel is a microkernel — resource limits are policy
• getrlimit() / setrlimit() → libc stubs with reasonable defaults
• Process enforcement → procmgr (userspace process manager) via proc: scheme
• File descriptor limits → already enforced via CONTEXT_MAX_FILES in kernel
• Memory limits → userspace procmgr can kill processes exceeding limits

// relibc implementation (userspace, no kernel changes needed):
fn getrlimit(resource: c_int, rlim: *mut rlimit) -> Result<()> {
    match resource {
        RLIMIT_NOFILE => { rlim.rlim_cur = 1024; rlim.rlim_max = 4096; }
        RLIMIT_NPROC =>  { rlim.rlim_cur = 256;  rlim.rlim_max = 1024; }
        RLIMIT_AS =>     { rlim.rlim_cur = RLIM_INFINITY; rlim.rlim_max = RLIM_INFINITY; }
        RLIMIT_CORE =>   { rlim.rlim_cur = 0;    rlim.rlim_max = RLIM_INFINITY; }
        // ... other resource types with reasonable defaults
        _ => return Err(Errno(EINVAL)),
    }
    Ok(())
}

K4.2 — PTRACE via proc: scheme

SYS_PTRACE is not implemented as a direct syscall. The Redox model uses the proc: scheme for process inspection and manipulation:

• Already partially implemented in scheme/proc.rs
• Memory read/write through proc: scheme file operations
• Register read/write through proc: scheme
• Signal injection through proc: scheme

Improvements needed:

• Document the proc: scheme ptrace API surface
• Ensure all ptrace operations have proc: scheme equivalents
• Add PTRACE_* constants to redox_syscall for compatibility

K4.3 — clock_settime

SYS_CLOCK_SETTIME returns ENOSYS. Implementation:

• Add scheme write path to /scheme/sys/update_time_offset
• Or implement as direct syscall for precision
• Priority: P3 — needed for NTP synchronization

Phase K5: Shutdown and Power Management (Week 5-7)

See local/docs/ACPI-IMPROVEMENT-PLAN.md for full ACPI plan. This section covers kernel-specific work only.

K5.1 — Hardened acpid Startup

• Remove panic-grade expect paths in kernel ACPI/AML handling
• Add graceful fallback when ACPI tables are missing or malformed
• See ACPI-IMPROVEMENT-PLAN.md Wave 1

K5.2 — kstop Shutdown Robustness

• Current: _S5 shutdown via kstop event exists but gated on PCI timing
• Required: deterministic shutdown ordering:
  1. Notify userspace services of impending shutdown
  2. Sync filesystems
  3. Power off via ACPI/FADT
• See ACPI-IMPROVEMENT-PLAN.md Wave 2

K5.3 — Sleep State Support

• S3 (suspend-to-RAM) and S4 (hibernate) are not yet supported
• Requires: kernel state serialization, device reinitialization
• Priority: P4 — long-term, not blocking desktop

5. Dependency Chain

Phase K1 (credential syscalls) ─────────────────────┐
    │                                                 │
    ├──► polkit compatibility                        │
    ├──► dbus-daemon credential checks                │
    ├──► sudo/su user switching                       │
    ├──► redbear-sessiond login1 handoff              │
    └──► greeter/session-launch credential drop        │
                                                      │
Phase K2 (access control) ────────────────────────────┤
    │                                                 │
    ├──► Privilege-separated boot sequence            │
    ├──► Scheme-level credential enforcement          │
    └──► initgroups() for service launching            │
                                                      │
Phase K3 (IPC) ───────────────────────────────────────┤
    │                                                 │
    ├──► POSIX message queues → needed by some apps   │
    ├──► AF_UNIX → broader D-Bus transport options    │
    └──► eventfd/signalfd/timerfd → KDE/Qt runtime     │
                                                      │
Phase K4 (limits/ptrace) ─────────────────────────────┤
    │                                                 │
    ├──► RLIMIT → systemd/logind compatibility        │
    ├──► PTRACE → debugging support                   │
    └──► clock_settime → NTP synchronization           │
                                                      ▼
                                          Desktop infrastructure
                                          ready for KDE Plasma

6. Integration with Existing Work

6.1 Already in Progress (do not duplicate)

Area	Canonical Plan	Status
IRQ / MSI-X / IOMMU	IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md	Waves 1-6 complete, hardware validation open
ACPI shutdown / power	ACPI-IMPROVEMENT-PLAN.md	Waves 1-2 complete, sleep states deferred
relibc IPC surface	RELIBC-IPC-ASSESSMENT-AND-IMPROVEMENT-PLAN.md	Phases I1-I5, message queues deferred
D-Bus / sessiond	DBUS-INTEGRATION-PLAN.md	Phase 1 complete, Phase 2 in progress
Greeter / login	GREETER-LOGIN-IMPLEMENTATION-PLAN.md	Active, bounded proof passing
Desktop path	CONSOLE-TO-KDE-DESKTOP-PLAN.md	Phase 1-5 model, KWin building

6.2 This Plan Covers (uniquely)

Area	This Plan	Not Covered By
Kernel credential architecture	§3, Phase K1	Any existing plan
Kernel access control hardening	§3.2, Phase K2	Any existing plan
setgroups() / getgroups() kernel implementation	Phase K1.2-K1.4	Only stub noted elsewhere
Supplementary group infrastructure	Phase K1.1	Not covered anywhere
POSIX/SysV message queues	Phase K3.1-K3.2	Deferred in relibc-IPC plan
UNIX domain sockets	Phase K3.3	Not covered
RLIMIT design decision	Phase K4.1	Noted as gap only
PTRACE via proc: scheme	Phase K4.2	Not covered
clock_settime implementation	Phase K4.3	Noted as gap only

7. Patch Governance

All kernel and relibc source changes must follow the durability policy (see local/AGENTS.md):

1. Make changes in recipes/core/kernel/source/ or recipes/core/relibc/source/
2. Generate patches: git diff in the source tree → local/patches/<component>/P4-*.patch
3. Wire patches into recipes/core/<component>/recipe.toml patches list
4. Commit patches + recipe changes before session end
5. Assume source trees may be thrown away by make distclean or upstream refresh

Patch naming convention:

local/patches/kernel/P4-credential-fields.patch
local/patches/kernel/P4-credential-syscalls.patch
local/patches/kernel/P4-redox-syscall-numbers.patch
local/patches/relibc/P4-setgroups-kernel.patch
local/patches/relibc/P4-getgroups-kernel.patch
local/patches/relibc/P4-redox-rt-cred-syscalls.patch
local/patches/relibc/P4-initgroups.patch

8. Validation and Evidence

8.1 Build Evidence

Check	Command
Kernel compiles	make r.kernel
relibc compiles	make r.relibc
Full OS builds	make all CONFIG_NAME=redbear-full

8.2 Runtime Evidence

Test	Verification
getuid() returns non-zero after login	id command in guest
setgroups() succeeds for root	sudo -u user id in guest
setresuid() properly changes euid	su user -c 'id'
initgroups() populates groups	groups command in guest
Credentials survive fork	bash -c 'id'
Credentials dropped on exec (if SUID implemented)	TBD
polkit can query credentials	pkexec echo ok
dbus-daemon starts without errors	dbus-monitor

8.3 Verification Scripts

Create bounded proof scripts:

local/scripts/test-credential-syscalls-qemu.sh    # QEMU launcher
local/scripts/test-credential-syscalls-guest.sh   # In-guest checker

9. References

• local/docs/COMPREHENSIVE-OS-ASSESSMENT.md — Canonical comprehensive plan
• docs/01-REDOX-ARCHITECTURE.md — Architecture reference
• local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md — IRQ/PCI plan (sibling)
• local/docs/RELIBC-IPC-ASSESSMENT-AND-IMPROVEMENT-PLAN.md — IPC surface plan (companion)
• local/docs/ACPI-IMPROVEMENT-PLAN.md — ACPI/shutdown plan (sibling)
• local/docs/CONSOLE-TO-KDE-DESKTOP-PLAN.md — Desktop path plan (consumer)
• recipes/core/kernel/source/src/syscall/mod.rs — Syscall dispatch (primary implementation target)
• recipes/core/kernel/source/src/context/context.rs — Context struct (credential fields)
• recipes/core/kernel/source/src/scheme/proc.rs — Proc scheme (credential setting)
• recipes/core/relibc/source/src/platform/redox/mod.rs — relibc Redox platform (credential stubs)
• recipes/core/relibc/source/redox-rt/src/sys.rs — redox-rt credential primitives