dotfiles: let the group read the kernel logger ACL it was granted

[dotfiles] / README.md

# dotfiles

Windows development-box provisioning scripts.

`setup-windows.bat` takes a fresh Windows install to a working C++ / native
development environment: editors and shells, Python, the Visual Studio 2022
toolchain (including the Clang and Windows XP targeting toolsets), the Windows
Driver Kit, and a handful of analysis tools (Sysinternals, OpenCppCoverage,
BinSkim, the Windows Performance Toolkit). It also sets the box up to be driven
remotely: OpenSSH Server plus an rsync build for Windows, which is what makes a
throwaway VM reachable from a Linux host.

## Files

| File | Purpose |
| --- | --- |
| `setup-windows.bat` | Entry point. Runs the winget installs, then launches the elevated half and prints its log, then runs the non-elevated script. |
| `setup-windows-no-uac.ps1` | The non-elevated, per-user half: WinMerge and BinSkim on the user `PATH`, and the global git config (identity, plus `core.sshCommand`). Can also be run directly from an ordinary prompt. |
| `setup-windows-with-uac.ps1` | The elevated half, started via UAC by the batch file. Enables `ssh-agent`, installs the OpenSSH Client and Server capabilities and starts `sshd`, unpacks the `rsync-windows` release zip for this architecture (`rsync.exe` plus the `ssh.exe` it runs) into `C:\Tools\rsync` on the machine `PATH`, then installs Visual Studio 2022 Community with the required components, the WDK, and the Windows Performance Toolkit, and finally grants one ordinary account the rights to collect ETW traces without elevation. Can also be run directly from an Administrator prompt — pass `-TraceUser DOMAIN\user` to say who gets those rights, and `-EtwRightsOnly` to do that step alone. |
| `setup-windows-7-test-env.bat` | Prepares a **Windows 7 VM** as a test target driven from the host by `VBoxManage guestcontrol`. Copy it into the guest and run it there; it is idempotent, so re-run it after any snapshot restore. The per-user half needs no UAC (crash-dialog suppression, no screen blanking, a staging directory, the shared folder on `Z:`); the machine-wide half is skipped with a notice unless run elevated inside the guest. It then reports what the box can actually test: DWM composition, printers, audio capture devices. |

## Usage

1. **Edit `setup-windows-no-uac.ps1` first.** The global git identity near the
   top of the file is empty:

   ```powershell
   $GitUserName  = ''   # e.g. 'Ada Lovelace'
   $GitUserEmail = ''   # e.g. 'ada@example.com'
   ```

   Fill in your own name and email, or leave them empty to keep your identity
   per-repository - the script skips `user.name` / `user.email` rather than
   writing a placeholder, and says so. Everything else in that script is set
   either way.

2. Run it from a normal (non-elevated) prompt:

   ```bat
   setup-windows.bat
   ```

   It will raise a single UAC prompt for the elevated half. Accept it — declining
   leaves Visual Studio and the WDK uninstalled, and the script says so.

3. Restart your shell afterwards so the updated user `PATH` is picked up, and
   reboot if a step reported that a restart was required.

## Notes

- The elevated half writes a transcript to `setup-windows-uac.log` next to the
  script; the batch file prints it when the elevated window closes. The log is
  gitignored, as it contains local paths.
- **git uses a Win32-OpenSSH client.** `setup-windows-no-uac.ps1` sets
  `core.sshCommand`. Git for Windows otherwise prefers its own bundled MSYS2
  `ssh.exe`, which cannot reach the Windows `ssh-agent` service that the elevated
  half enables - Win32-OpenSSH publishes the agent on a named pipe the MSYS2
  build does not speak. Without this, keys loaded with `ssh-add` from PowerShell
  are invisible to `git`, and a push falls back to hunting for a key file and
  prompting for its passphrase. The value uses forward slashes on purpose: git
  parses `core.sshCommand` with shell quoting rules, in which a backslash is an
  escape character.
- **Which `ssh.exe` git gets.** `C:\Tools\rsync\ssh.exe` — the fast build the
  elevated half unpacks — if it is there, `%WINDIR%/System32/OpenSSH/ssh.exe`
  otherwise. It is the same client with the same `~/.ssh`, agent and
  `known_hosts`; the difference is the stdin pump, and without it anything git
  *pushes* is capped at ~17 MB/s. Candidates are tried by **running** them
  (`ssh -V`), not by `Test-Path`: the fast build needs a `libcrypto.dll` that an
  image without the OpenSSH Client capability does not have, and a client that
  will not start should be found here rather than on the next `git push`.
  This is also why `setup-windows.bat` now runs the elevated half **first** — the
  fast `ssh.exe` has to exist before the git config step can prefer it. The
  non-elevated half still runs even when the elevated one failed; it just falls
  back. Re-run `setup-windows-no-uac.ps1` on its own at any time to re-pick.
- All three scripts are idempotent — re-running skips anything already installed.
  BinSkim in particular checks NuGet for the newest stable version *before*
  downloading: the package is a self-contained .NET build well over 100 MB, and
  re-provisioning an up-to-date box should not pay for it. The installed version
  is tracked in `nupkg-version.txt` beside the tool.
- `setup-windows-no-uac.ps1` runs its steps independently: one failing warns and
  the rest still run, and it exits 1 if any did. The `.bat` reports that and
  carries on to the elevated half, which is the part worth the UAC prompt. Use
  `-Skip` to re-run a subset, e.g. `.\setup-windows-no-uac.ps1 -Skip BinSkim`.
  Run it **non-elevated**: it writes per-user state (the `HKCU` `PATH`, the
  `.gitconfig` under `%USERPROFILE%`), so an elevated run would configure the
  administrator's profile instead. It warns if you do.
- **Remote access.** OpenSSH Server is installed from the Windows on-demand
  capability (10/1809+), set to start automatically, and given an inbound TCP 22
  firewall rule on *all* profiles — a VM's host-only or bridged adapter is
  routinely classified Public, which is the usual reason a running `sshd` is
  unreachable. Windows ships no `rsync`, so a build of it
  ([nuket/rsync-windows](https://github.com/nuket/rsync-windows)) is installed to
  `C:\Tools\rsync` and added to the **machine** `PATH`. That last detail matters:
  the remote end of an `rsync` runs non-interactively, with no login shell, and
  Win32-OpenSSH builds that environment from the registry `PATH` rather than from
  a profile. Key auth needs `~/.ssh/authorized_keys` ACL'd to just you and
  `SYSTEM`; accounts in the Administrators group use
  `C:\ProgramData\ssh\administrators_authorized_keys` instead.
- **rsync brings its own `ssh.exe`.** That release ships as one zip per
  architecture — `rsync-windows-x64.zip` / `rsync-windows-x86.zip`, each holding
  `rsync.exe`, an `ssh.exe`, `COPYING.txt` and `NOTICE-ssh.txt` — and the
  elevated half picks the zip for the OS bitness, verifies it against the
  published `.sha256`, and unpacks the pair together. Together is the point:
  `rsync.exe` prefers an `ssh.exe` sitting in its own directory, and the release
  builds one because the client Windows ships reads its stdin 3 KB at a time,
  which holds a transfer *from* the box at ~17 MB/s however fast the link is.
  Nothing else about it differs — same `~/.ssh`, same `ssh-agent`, same
  `known_hosts` — and a bare `ssh` still resolves to the in-box client, which
  sits ahead of `C:\Tools\rsync` on the `PATH`. It links against the
  `libcrypto.dll` the **OpenSSH Client** capability puts in `System32` (Windows'
  own LibreSSL, which uses AES-NI) and ships no copy of its own, so the elevated
  half installs that capability first and falls back to `rsync.exe` alone,
  warning, on an image that will not offer it.
- The `rsync` download follows the `releases/latest/download/` redirect rather
  than the GitHub API: unauthenticated API calls are rate-limited to 60/hour per
  IP, which a provisioning run behind a shared NAT can genuinely exhaust. To hold
  a box on a known build, pin the tag in `$RsyncUrl`
  (`.../releases/download/<tag>/<asset>`) instead.
- Visual Studio is installed in three labelled passes (base workload, Clang/LLVM,
  XP toolset) so a failure identifies which component group is responsible.
- **Windows Performance Analyzer is not part of Visual Studio.** VS has its own
  Performance Profiler, which is a different, `.diagsession`-based tool and
  cannot open an `.etl`. WPA ships with `xperf` and `wpr` in the Windows
  Performance Toolkit, which exists in exactly two places: as an optional
  *feature* of the Windows SDK (`OptionId.WindowsPerformanceToolkit`) and inside
  the Windows ADK, which bundles the same toolkit. Whether the SDK install that
  Visual Studio performs selects that feature varies by version, so the elevated
  half **detects first** — `%ProgramFiles(x86)%\Windows Kits\10\Windows
  Performance Toolkit`, its 64-bit twin, and the ADK location — and only falls
  back to `winget install Microsoft.WindowsADK` when nothing is there. It then
  re-asserts that directory on the machine `PATH` (the toolkit's own installer
  usually does this, and the Start Menu gets *Windows Kits > Windows Performance
  Toolkit* shortcuts for WPA and WPR). To install just the toolkit instead of the
  whole ADK, run the standalone SDK setup with
  `winsdksetup.exe /features OptionId.WindowsPerformanceToolkit /q`. A newer WPA
  also exists in the Microsoft Store (`winget install --id 9N0W1B2BXGNZ --source
  msstore`); it is not installed here because the Store source needs an
  interactive, signed-in session, which the unattended elevated half does not
  have.
- **Tracing without a UAC prompt.** `xperf` and `wpr` fail for a standard user in
  two different ways, because two different things are missing:

  ```text
  xperf -on base             -> NT Kernel Logger: Access is denied. (0x5)
  wpr -start GeneralProfile  -> Failed to enable the policy to profile system performance.
  ```

  Three separate things are in the way, and all three have to be dealt with:

  1. Creating or controlling *any* ETW session — even a user-mode one naming a
     single provider — is checked against the security descriptor ETW keeps per
     provider GUID under `HKLM\SYSTEM\CurrentControlSet\Control\WMI\Security`,
     whose **default** grants the session-control rights to SYSTEM,
     Administrators, the service accounts and `BUILTIN\Performance Log Users`,
     and to nobody else.
  2. Switching on the *kernel* provider needs the `SeSystemProfilePrivilege` user
     right ("Profile system performance"), held by default only by
     Administrators and `NT SERVICE\WdiServiceHost` — that is the one `wpr`
     names.
  3. The kernel logger is not covered by that default descriptor.
     `SystemTraceControlGuid` — the session both `xperf -on` and `wpr` drive —
     carries an explicit one that does not mention Performance Log Users. With
     1 and 2 in place a user-mode session starts and the privilege is held, and
     `xperf -on base` *still* answers "NT Kernel Logger: Access is denied" while
     `wpr`'s error changes to a bare `0x80070005`; even reading that descriptor
     comes back access-denied, which is the tell. So an ACE for the group is
     added with `EventAccessControl`, `TRACELOG_ACCESS_KERNEL_LOGGER` included.

  The privilege and the ACE both go to the **group**, and the account then goes
  into the group, so membership alone is the switch and enabling another account
  afterwards is just `net localgroup "Performance Log Users" <user> /add`.
  `SeDebugPrivilege` is deliberately *not* granted: CPU sampling and stack walks
  of your own processes do not need it, and it is equivalent to handing out
  administrator. Worth being clear about the cost: a member of that group can
  capture system-wide kernel traces — process, image, file and registry activity
  across every account on the box, paths and command lines included.

  Two consequences worth knowing. A privilege and a group membership are both
  read into the access token **at logon**, so the account must sign out and back
  in for 1 and 2 — any new logon does it, and an `ssh` login into the box is the
  quick way to check without dropping the desktop. The ACE in 3 is machine state
  instead, and a logon does nothing for it: ETW reads these descriptors into a
  cache, so it takes a **reboot** — with the ACE written and readable, `xperf -on
  base` was still denied from a fresh shell on the running system. Plan on both
  on a first run. And this only
  helps a **non-admin** account: UAC hands an administrator a filtered token
  carrying just five harmless privileges, so an admin's ordinary shell still
  cannot trace however the policy reads. Verify from the target account,
  unelevated:

  ```powershell
  whoami /priv | findstr SeSystemProfilePrivilege
  xperf -on base ; xperf -stop C:\Temp\trace.etl
  ```

  Analysis never needed any of this — `wpa.exe` opens an existing `.etl` as a
  plain user. This is only about collection.

  The rights step runs **first** in the elevated half, and `-EtwRightsOnly` runs
  it and nothing else. It is seconds of LSA and registry work where a full run is
  dominated by the three Visual Studio passes, which take minutes even with
  nothing to do:

  ```powershell
  Start-Process powershell -Verb RunAs -ArgumentList '-NoProfile','-ExecutionPolicy','Bypass',
      '-File','<repo>\setup-windows-with-uac.ps1','-TraceUser','DOMAIN\user','-EtwRightsOnly'
  ```
- The scripts were extracted from a native Windows project, so the component
  selection is tuned for that: Spectre-mitigated runtimes, the v141/XP toolset,
  and driver-kit headers. Trim the component lists in the `.ps1` if you don't
  need them — each group is a plain array near the top.