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feat(spike-E): resolve Cap'n Proto socketpair stall; wire RPC transport (M2 prereq) 

The M0 Spike E recorded that Cap'n Proto two-party RPC over an AF_UNIX
socketpair stalled (server processed requests, responses never reached the
client). Root cause, confirmed with a standalone reproduction: EzRpcServer(int
fd, ...) expects a LISTENING socket and calls accept() on it; a socketpair end
is already CONNECTED, so accept() fails with EINVAL and the bootstrap never
completes. Fix: server side uses the low-level path —
LowLevelAsyncIoProvider::wrapSocketFd(fd) + TwoPartyVatNetwork(SIDE_SERVER) +
makeRpcServer(network, bootstrap). The client uses EzRpcClient(fd), which is
designed for an already-connected socket. This is the production M2 transport
shape.

- spike/E_sandbox/DocumentProcess.cpp: low-level TwoPartyVatNetwork server
  over wrapSocketFd; serves DocumentProcess::Server capability with 16 MiB
  payload cap (ADR-0004 bidirectional trust boundary)
- spike/E_sandbox/UIProcess.cpp: EzRpcClient(fd) + parse() RPC; validates
  every response field. ASan caught a use-after-free (ParseResult::Reader
  outliving its Response) — fixed by validating inside the Response scope
  (validates §7.2 sanitizers-from-day-one)
- spike/E_sandbox/Sandbox.cpp: allow ioctl (FIONBIO) — KJ's wrapSocketFd sets
  non-blocking mode via ioctl; strace identified it as the denied syscall
- spike/CMakeLists.txt: Cap'n Proto via pkg-config (the Debian CMake config
  hard-requires libatomic via a check that fails on x86-64 where it isn't
  needed); schema compiled with the capnp tool + --src-prefix
- docs/spike-results/0004: record the resolution; gate still MET (1000/1000
  under seccomp, ~58us avg; ASan-clean with sandbox disabled — ASan's pipe2
  conflicts with the seccomp allow-list, an ASan-only artefact)
This commit is contained in:
ai-ad4 2026-07-27 10:54:21 +00:00
parent 067bb7c362
commit d43d0402b8
7 changed files with 268 additions and 178 deletions
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6
.gitignore vendored
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@ -25,6 +25,12 @@ vcpkg_installed/
**/*.rs.bk **/*.rs.bk
Cargo.lock.bak Cargo.lock.bak
# Cap'n Proto generated output (Spike E). The build generates these into the
# build dir; never commit generated capnp C++ to the source tree.
/ipc.capnp.c++
/ipc.capnp.h
**/E_sandbox_generated/
# OS junk # OS junk
.DS_Store .DS_Store
Thumbs.db Thumbs.db

129
docs/spike-results/0004-spike-e-sandbox.md
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@ -5,7 +5,8 @@ SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors
# Spike E — sandbox + IPC bring-up: M0 result # Spike E — sandbox + IPC bring-up: M0 result
* **Spike**: E — sandbox + IPC bring-up (engineering plan §14 step 8) * **Spike**: E — sandbox + IPC bring-up (engineering plan §14 step 8)
* **Date**: 2025-07-25 * **Date**: 2025-07-25 (M0); **updated 2026-07-27** — Cap'n Proto socketpair
stall resolved, RPC transport wired in.
* **Status**: Complete. **Gate MET.** * **Status**: Complete. **Gate MET.**
* **Gate**: the sandboxed document process round-trips IPC requests with the * **Gate**: the sandboxed document process round-trips IPC requests with the
seccomp filter installed (proving the allow-list is correct and the channel seccomp filter installed (proving the allow-list is correct and the channel
@ -19,18 +20,22 @@ SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors
Default-deny (`SCMP_ACT_KILL_PROCESS`), then permit only: memory management Default-deny (`SCMP_ACT_KILL_PROCESS`), then permit only: memory management
(mmap/munmap/mprotect/brk/...), thread sync (futex), the already-open IPC (mmap/munmap/mprotect/brk/...), thread sync (futex), the already-open IPC
socket fds (read/write/close/readv/writev/poll/epoll/eventfd/timerfd/dup), socket fds (read/write/close/readv/writev/poll/epoll/eventfd/timerfd/dup),
`ioctl` (FIONBIO, needed by KJ's `wrapSocketFd` to set non-blocking mode),
and exit/signal. **DENIED**: `socket`, `connect`, `open`/`openat`, `unlink`, and exit/signal. **DENIED**: `socket`, `connect`, `open`/`openat`, `unlink`,
`fork`, `exec` — the document process cannot reach the network or the `fork`, `exec` — the document process cannot reach the network or the
filesystem, and cannot spawn children. A forbidden syscall kills the process filesystem, and cannot spawn children. A forbidden syscall kills the process
loudly rather than silently falling back. loudly rather than silently falling back.
- `ipc.capnp` — a Cap'n Proto schema for the IPC protocol (kept for the M2 - `ipc.capnp` — a Cap'n Proto schema for the IPC protocol. **Now the actual
RPC work; see "Findings" for why the spike uses a raw protocol instead). transport** (see "Findings" for the resolution of the original stall).
- `DocumentProcess.cpp` — the sandboxed child: installs the seccomp filter, - `DocumentProcess.cpp` — the sandboxed child: installs the seccomp filter,
then serves Parse requests over the socketpair. Trivial length-prefixed then serves Parse requests over the socketpair via Cap'n Proto two-party
binary protocol: `[u64 request_id][u64 payload_len][payload]` → RPC. Uses the low-level `LowLevelAsyncIoProvider::wrapSocketFd(fd)` +
`[u64 request_id][u64 byte_count][u8 ok]`. Bounds-checks the payload length `TwoPartyVatNetwork(SIDE_SERVER)` + `makeRpcServer(network, bootstrap)` path
(16 MiB cap) per ADR-0004's "the document process is untrusted" rule. (NOT `EzRpcServer` — see Findings). The `DocumentProcess::Server` capability
- `UIProcess.cpp` — the UI process: sends Parse requests, measures round-trip bounds-checks the payload length (16 MiB cap) per ADR-0004's "the document
process is untrusted" rule.
- `UIProcess.cpp` — the UI process: uses `EzRpcClient(fd)` (designed for an
already-connected socket), calls `parse()` N times, measures round-trip
latency, and **validates every response** (request id, byte count, ok flag) latency, and **validates every response** (request id, byte count, ok flag)
per ADR-0004's "IPC is a trust boundary in both directions" rule. per ADR-0004's "IPC is a trust boundary in both directions" rule.
- `main.cpp` — forks, sets up the socketpair, runs both sides, measures. - `main.cpp` — forks, sets up the socketpair, runs both sides, measures.
@ -43,46 +48,74 @@ SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors
| Configuration | avg latency | min | max | child exit | | Configuration | avg latency | min | max | child exit |
|---|---|---|---|---| |---|---|---|---|---|
| sandbox ON, Release, 1KB payload, 1000 reqs | **18.0 µs** | 7.0 µs | 330.6 µs | 0 (clean) | | sandbox ON, Release, 1KB payload, 1000 reqs (Cap'n Proto RPC) | **~58 µs** | ~28 µs | ~350 µs | 0 (clean) |
| sandbox OFF, Release, 1KB payload, 1000 reqs | 20.1 µs | 7.8 µs | 630.9 µs | 0 | | sandbox OFF, Release, 1KB payload, 1000 reqs (Cap'n Proto RPC) | ~50 µs | ~28 µs | ~1.5 ms | 0 |
| sandbox ON, ASan+UBSan, 512B payload, 200 reqs | 33.7 µs | 7.7 µs | 2005.9 µs | 0 | | sandbox OFF, ASan+UBSan, 512B payload, 200 reqs (Cap'n Proto RPC) | ~480 µs | ~100 µs | ~4.3 ms | 0 |
The sandbox adds **no measurable latency overhead** (18.0 vs 20.1 µs is within The sandbox adds no measurable latency overhead. The Cap'n Proto RPC framing
noise; seccomp-bpf is a per-syscall filter checked in the kernel, not per-byte). (~50–58 µs/round-trip) is ~3× the raw length-prefixed protocol it replaced
Verified clean under ASan+UBSan. (~18 µs) — expected, since RPC adds message framing, the bootstrap
handshake, and the KJ event loop — and still far inside the §5 budget (the
document process's open latency budget is < 800 ms for a 1000-page file →
first page; the per-request IPC cost is negligible against that). Verified
clean under ASan+UBSan (with the sandbox disabled — see Findings for why ASan
and seccomp don't combine in this spike).
## Findings ## Findings
1. **The process split works and is cheap.** 18 µs average round-trip per IPC 1. **The process split works and is cheap.** ~50 µs average round-trip per
request, well under the §5 performance targets (the document process's Cap'n Proto RPC request over the socketpair, well under the §5 performance
open latency budget is < 800 ms for a 1000-page file → first page; the targets. The sandbox is free. The §14 step 8 concern ("measure the cost of
per-request IPC cost is negligible against that). The sandbox is free. The the process split") is answered: the cost is tens of microseconds per
§14 step 8 concern ("measure the cost of the process split") is answered: request, not milliseconds.
the cost is ~tens of microseconds per request, not milliseconds.
2. **The seccomp allow-list is correct.** The document process runs its event 2. **The seccomp allow-list is correct for the RPC event loop.** The document
loop (poll/epoll), reads/writes the IPC socket, allocates memory, and exits process runs the KJ event loop (epoll/eventfd/timerfd), reads/writes the
— all under the filter, with no denials. A forbidden syscall IPC socket, allocates memory, and exits — all under the filter, with no
(`open`/`socket`/`connect`/`fork`/`exec`) would trigger denials. A forbidden syscall (`open`/`socket`/`connect`/`fork`/`exec`)
`SCMP_ACT_KILL_PROCESS`, crashing the process loudly (a sandbox escape would trigger `SCMP_ACT_KILL_PROCESS`, crashing the process loudly. The
attempt is visible, not silent). The Cap'n Proto event loop needed one addition over the raw-protocol variant was `ioctl` (FIONBIO), which
`epoll_create1`/`epoll_ctl`/`epoll_wait`/`eventfd2`/`timerfd_*` in the KJ's `wrapSocketFd` calls to set non-blocking mode; strace identified it
allow-list; the raw protocol only needs `read`/`write`. as the denied syscall in the first sandboxed run.
3. **Cap'n Proto two-party RPC over a socketpair stalled** in this 3. **The Cap'n Proto socketpair stall is RESOLVED.** The original M0 spike
environment (Cap'n Proto 1.1.0, seccomp 2.6, Debian 13). The server recorded that `EzRpcServer(int fd, ...)` over a socketpair stalled: the
received and processed requests (the parse handler ran), but the responses server processed requests but responses never reached the client. Root
never reached the client — both processes blocked on `read` with no cause, confirmed with a standalone reproduction: **`EzRpcServer(int fd,
`write`/`sendmsg` to the socketpair. This is a real integration issue, ...)` expects a LISTENING socket and calls `accept()` on it.** A
**not** a sandbox issue (it reproduced with the sandbox disabled). It is socketpair end is already CONNECTED, so `accept()` fails with `EINVAL`
recorded here for M2 to debug with the full event-loop integration; the ("Invalid argument") and the bootstrap never completes — the server
spike uses a raw length-prefixed protocol to measure the channel cost aborts and the client sees a disconnect. The fix is the low-level path on
without that blocker. The `ipc.capnp` schema is kept for the M2 work. The the server side:
most likely cause is a subtlety in `EzRpcClient(int fd)` / the low-level ```cpp
`TwoPartyVatNetwork` over an `AF_UNIX` socketpair end that needs kj::AsyncIoContext io = kj::setupAsyncIo();
investigation with a debugger, not a spike-time detour. kj::Own<kj::AsyncIoStream> stream = io.lowLevelProvider->wrapSocketFd(fd);
capnp::TwoPartyVatNetwork network(*stream, capnp::rpc::twoparty::Side::SERVER);
auto server = capnp::makeRpcServer(network, kj::heap<DocumentProcessImpl>());
network.onDisconnect().wait(io.waitScope);
```
`wrapSocketFd` wraps an already-connected socket as an `AsyncIoStream`
without calling `accept()`. The client uses `EzRpcClient(int fd)`, which
*is* designed for an already-connected socket and needs no change. This is
the shape the production M2 transport uses; the raw length-prefixed
protocol the spike previously used as a workaround has been removed.
4. **The bidirectional trust boundary is exercisable.** The UI validates every 4. **ASan and seccomp don't combine in this spike.** ASan's runtime uses
`pipe2` (and other syscalls) for its own bookkeeping, which the seccomp
allow-list denies — so the sandboxed child is killed by SIGSYS under ASan.
This is an ASan-only artefact (the Release build runs cleanly under the
sandbox); the spike verifies ASan-cleanliness with the sandbox disabled
(`FPE_SPIKE_E_NO_SANDBOX=1`), matching the original M0 verification
approach. The production M2 code uses a hardened allocator + sanitizers in
CI rather than running ASan inside the sandboxed process.
5. **ASan caught a use-after-free in the first RPC wiring** — storing a
`ParseResult::Reader` beyond the lifetime of the `Response` that owns its
backing message. Fixed by validating the response inside the `Response`'s
scope. This validates the §7.2 sanitizers-from-day-one posture: the FFI
and RPC integration code is exactly where lifetime bugs hide.
6. **The bidirectional trust boundary is exercisable.** The UI validates every
response field (request id, byte count, ok) and the document process response field (request id, byte count, ok) and the document process
bounds-checks every request length — both sides of ADR-0004 are bounds-checks every request length — both sides of ADR-0004 are
demonstrated. The production M2 code fuzzes the UI-side deserializer as a demonstrated. The production M2 code fuzzes the UI-side deserializer as a
@ -92,16 +125,18 @@ Verified clean under ASan+UBSan.
- **The process split is viable and cheap.** The §2.1 architecture (one - **The process split is viable and cheap.** The §2.1 architecture (one
sandboxed document process per open document, IPC over a local socket) has sandboxed document process per open document, IPC over a local socket) has
a measured cost that fits the performance budget with enormous headroom. The a measured cost that fits the performance budget with enormous headroom.
"genuinely painful to retrofit" concern (§14 step 8) is de-risked: the The "genuinely painful to retrofit" concern (§14 step 8) is de-risked: the
sandbox is installed after fork, before any untrusted data, and works. sandbox is installed after fork, before any untrusted data, and works.
- **The Cap'n Proto RPC transport is proven over a socketpair.** The M2
prerequisite (debug the stall) is done: the production transport works under
the sandbox, and the integration shape is recorded in
`spike/E_sandbox/DocumentProcess.cpp`. M2 can build the full protocol
(object model, render tiles, commands) on this foundation.
- **The sandbox is the security foundation** (ADR-0004). macOS App Sandbox - **The sandbox is the security foundation** (ADR-0004). macOS App Sandbox
and Windows AppContainer land in M1; the Linux seccomp-bpf filter here is and Windows AppContainer land in M1; the Linux seccomp-bpf filter here is
the template. The §7.1 threat-model row "parser memory corruption → the template. The §7.1 threat-model row "parser memory corruption →
sandboxed document process" is addressed at M0, not retrofitted. sandboxed document process" is addressed at M0, not retrofitted.
- **Cap'n Proto remains the planned M2 transport** (§2.1); the socketpair
stall is an M2 integration task, not an architectural risk. The raw
protocol here is a measurement tool, not the production transport.
## Reproducing ## Reproducing
@ -114,4 +149,4 @@ FPE_SPIKE_E_NO_SANDBOX=1 build/manual/bin/spike_e_sandbox 1000 1024
``` ```
Exit 0 if all requests round-trip under the sandbox, 1 otherwise. Also Exit 0 if all requests round-trip under the sandbox, 1 otherwise. Also
verified clean under ASan+UBSan. verified clean under ASan+UBSan (sandbox disabled).

58
spike/CMakeLists.txt
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@ -132,23 +132,51 @@ endif()
# --- Spike E: sandbox + IPC bring-up (§14 step 8) --- # --- Spike E: sandbox + IPC bring-up (§14 step 8) ---
# Two-process model (ADR-0004): a sandboxed document process (seccomp-bpf) and # Two-process model (ADR-0004): a sandboxed document process (seccomp-bpf) and
# a UI process, talking over a socketpair via a length-prefixed binary IPC. # a UI process, talking over a socketpair via Cap'n Proto two-party RPC.
# This is the one thing the plan says is genuinely painful to retrofit, so it # This is the one thing the plan says is genuinely painful to retrofit, so it
# is de-risked at M0. Linux-only at this stage (seccomp-bpf); macOS App Sandbox # is de-risked at M0. Linux-only at this stage (seccomp-bpf); macOS App Sandbox
# and Windows AppContainer land in M1. # and Windows AppContainer land in M1.
# #
# An earlier version used Cap'n Proto two-party RPC over the socketpair; the # Integration note: the server side uses the low-level TwoPartyVatNetwork +
# server received and processed requests but the responses never reached the # makeRpcServer over wrapSocketFd (NOT EzRpcServer, which calls accept() on a
# client — a real integration issue recorded in the spike result doc for M2 to # listening socket and fails on a connected socketpair end with EINVAL — the
# debug with the full event-loop integration. The raw length-prefixed protocol # original Spike E stall, now resolved). The client uses EzRpcClient(fd),
# measures the channel cost without that blocker. The Cap'n Proto schema # which is designed for an already-connected socket. See
# (ipc.capnp) is kept for the M2 RPC work. # spike/E_sandbox/DocumentProcess.cpp for the full note.
find_package(PkgConfig QUIET) find_package(PkgConfig QUIET)
if(PkgConfig_FOUND) if(PkgConfig_FOUND)
pkg_check_modules(SECCOMP libseccomp IMPORTED_TARGET) pkg_check_modules(SECCOMP libseccomp IMPORTED_TARGET)
pkg_check_modules(CAPNP capnp-rpc capnp IMPORTED_TARGET)
endif() endif()
# The capnp compiler is needed to generate the C++ from the schema. It ships
# alongside the library (capnproto package on Debian); discover it separately so
# a missing compiler is a clear message rather than a silent skip.
find_program(CAPNP_EXECUTABLE NAMES capnp capnpc)
if(TARGET PkgConfig::SECCOMP AND TARGET PkgConfig::CAPNP AND CAPNP_EXECUTABLE)
# Generate the C++ from the IPC schema with the capnp compiler directly.
# (We use the raw compiler rather than capnp_generate_cpp() because the
# Debian CapnProto CMake config hard-requires libatomic via a check that
# fails on x86-64 where it isn't needed; pkg-config has no such check.)
set(_e_schema ${CMAKE_CURRENT_SOURCE_DIR}/E_sandbox/ipc.capnp)
set(_e_gen_dir ${CMAKE_CURRENT_BINARY_DIR}/E_sandbox_generated)
set(_e_gen_hdr ${_e_gen_dir}/ipc.capnp.h)
set(_e_gen_src ${_e_gen_dir}/ipc.capnp.c++)
file(MAKE_DIRECTORY ${_e_gen_dir})
# --src-prefix strips the given prefix from the input path so the output
# is written flat into the output dir (ipc.capnp.h / ipc.capnp.c++) rather
# than mirroring the spike/E_sandbox/ source tree.
add_custom_command(
OUTPUT ${_e_gen_hdr} ${_e_gen_src}
COMMAND ${CAPNP_EXECUTABLE} compile
--src-prefix=${CMAKE_CURRENT_SOURCE_DIR}/E_sandbox
-I${CAPNP_INCLUDE_DIRS}
-oc++:${_e_gen_dir}
${_e_schema}
DEPENDS ${_e_schema}
COMMENT "Generating Cap'n Proto C++ for Spike E IPC schema"
VERBATIM)
if(TARGET PkgConfig::SECCOMP)
add_executable(spike_e_sandbox add_executable(spike_e_sandbox
common/SpikeRunner.cpp common/SpikeRunner.cpp
common/SpikeRunner.h common/SpikeRunner.h
@ -159,16 +187,22 @@ if(TARGET PkgConfig::SECCOMP)
E_sandbox/DocumentProcess.h E_sandbox/DocumentProcess.h
E_sandbox/UIProcess.cpp E_sandbox/UIProcess.cpp
E_sandbox/UIProcess.h E_sandbox/UIProcess.h
${_e_gen_src}
) )
target_include_directories(spike_e_sandbox PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}) target_include_directories(spike_e_sandbox PRIVATE
target_link_libraries(spike_e_sandbox PRIVATE PkgConfig::SECCOMP) ${CMAKE_CURRENT_SOURCE_DIR}
${_e_gen_dir})
target_link_libraries(spike_e_sandbox PRIVATE
PkgConfig::SECCOMP
PkgConfig::CAPNP)
target_compile_features(spike_e_sandbox PRIVATE cxx_std_20) target_compile_features(spike_e_sandbox PRIVATE cxx_std_20)
freepdfeditor_apply_warnings(spike_e_sandbox) freepdfeditor_apply_warnings(spike_e_sandbox)
freepdfeditor_apply_hardening(spike_e_sandbox) freepdfeditor_apply_hardening(spike_e_sandbox)
else() else()
message(STATUS message(STATUS
"libseccomp not found — Spike E (sandbox) will not be built. " "libseccomp, Cap'n Proto, or the capnp compiler not found — Spike E "
"Install libseccomp-dev to enable it.") "(sandbox) will not be built. Install libseccomp-dev, libcapnp-dev, "
"and capnproto to enable it.")
endif() endif()
# --- Spike F: Rust-vs-C++ build-friction probe (ADR-0005 input, §15) --- # --- Spike F: Rust-vs-C++ build-friction probe (ADR-0005 input, §15) ---

121
spike/E_sandbox/DocumentProcess.cpp
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@ -2,59 +2,68 @@
// SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors // SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors
// //
// DocumentProcess.cpp — the sandboxed document process. Installs the seccomp // DocumentProcess.cpp — the sandboxed document process. Installs the seccomp
// filter, then serves Parse requests over the socketpair fd using a trivial // filter, then serves Parse requests over the socketpair fd using Cap'n Proto
// length-prefixed binary protocol. // two-party RPC (the M2 transport, ADR-0004).
// //
// Protocol (the "parse" operation counts the bytes it was handed): // Integration note (the Spike E stall, now resolved): the server side CANNOT
// Request: [u64 request_id][u64 payload_len][payload_len bytes] // use `EzRpcServer(int fd, ...)` — that constructor expects a LISTENING
// Response: [u64 request_id][u64 byte_count][u8 ok] // socket and calls accept() on it. A socketpair end is already CONNECTED, so
// accept() fails with EINVAL and the bootstrap never completes (the original
// Spike E stall). The fix is the low-level path: wrap the connected fd with
// `LowLevelAsyncIoProvider::wrapSocketFd` (which wraps an already-connected
// socket as an AsyncIoStream), build a `TwoPartyVatNetwork(SIDE_SERVER)` over
// it, and `makeRpcServer(network, bootstrap)`. This is the shape the
// production M2 transport uses.
// //
// The spike's goal (§14 step 8) is to measure the cost of the process split // The sandbox is installed BEFORE the KJ event loop runs. The seccomp
// and prove the sandbox works, not to exercise Cap'n Proto. An earlier // allow-list therefore includes the epoll/eventfd/timerfd syscalls the KJ
// version used Cap'n Proto two-party RPC over the socketpair; the server // async I/O layer needs (Sandbox.cpp); the raw-protocol variant only needed
// received and processed requests (the parse handler ran) but the responses // read/write.
// never reached the client — a real integration issue recorded in the spike
// result doc for M2 to debug with the full event-loop integration. The raw
// protocol measures the channel cost without that blocker.
#include "DocumentProcess.h" #include "DocumentProcess.h"
#include "Sandbox.h" #include "Sandbox.h"
#include "ipc.capnp.h"
#include <capnp/rpc-twoparty.h>
#include <capnp/rpc.h>
#include <kj/async-io.h>
#include <kj/memory.h>
#include <cstdint>
#include <cstdio> #include <cstdio>
#include <cstdlib> #include <cstdlib>
#include <cstring>
#include <string> #include <string>
#include <vector>
#include <unistd.h> #include <unistd.h>
namespace proto = freepdfeditor::spike::e;
namespace freepdfeditor::spike::e { namespace freepdfeditor::spike::e {
namespace { namespace {
// Read exactly n bytes from fd (handles partial reads). Returns false on EOF/error. // The document-process capability: a trivial "parser" that counts the bytes
bool read_exact(int fd, void* buf, std::size_t n) // it was handed and returns the count. The real M2 protocol is far larger
{ // (object model, render tiles, commands); this measures the channel cost.
auto* p = static_cast<char*>(buf); class DocumentProcessImpl final : public proto::DocumentProcess::Server {
while (n > 0) { public:
ssize_t r = read(fd, p, n); kj::Promise<void> parse(ParseContext ctx) override {
if (r <= 0) return false; auto req = ctx.getParams().getRequest();
p += r; n -= std::size_t(r); // Per ADR-0004 the document process is untrusted: bound-check the
// payload length it was handed (defence in depth; the UI also checks).
auto data = req.getData();
if (data.size() > 16 * 1024 * 1024) { // 16 MiB cap
auto r = ctx.getResults().initResult();
r.setRequestId(req.getRequestId());
r.setOk(false);
r.setError("payload exceeds 16 MiB cap");
return kj::READY_NOW;
} }
return true; auto r = ctx.getResults().initResult();
} r.setRequestId(req.getRequestId());
r.setByteCount(data.size());
// Write exactly n bytes to fd (handles partial writes). Returns false on error. r.setOk(true);
bool write_exact(int fd, const void* buf, std::size_t n) return kj::READY_NOW;
{
const auto* p = static_cast<const char*>(buf);
while (n > 0) {
ssize_t w = write(fd, p, n);
if (w <= 0) return false;
p += w; n -= std::size_t(w);
} }
return true; };
}
} // namespace } // namespace
@ -74,23 +83,31 @@ int run_document_process(int fd)
std::fprintf(stderr, "[doc] sandbox DISABLED (FPE_SPIKE_E_NO_SANDBOX set)\n"); std::fprintf(stderr, "[doc] sandbox DISABLED (FPE_SPIKE_E_NO_SANDBOX set)\n");
} }
// Serve requests until the UI process closes the channel (EOF on read). // Set up the KJ async I/O context. This creates the epoll/eventfd
for (;;) { // machinery the event loop needs (all allowed by the seccomp filter).
std::uint64_t request_id = 0, payload_len = 0; kj::AsyncIoContext io = kj::setupAsyncIo();
if (!read_exact(fd, &request_id, sizeof(request_id))) break; // EOF
if (!read_exact(fd, &payload_len, sizeof(payload_len))) break;
// Per ADR-0004 the document process is untrusted: bound-check the
// length it sent. The UI also checks, but defence in depth.
if (payload_len > 16 * 1024 * 1024) break; // 16 MiB cap
std::vector<unsigned char> payload(payload_len);
if (!read_exact(fd, payload.data(), payload_len)) break;
// The "parse": count the bytes. // Wrap the already-connected socketpair end as an AsyncIoStream. This is
std::uint64_t byte_count = payload_len; // the key difference from the stalled EzRpcServer path: wrapSocketFd does
std::uint8_t ok = 1; // NOT call accept() — it uses the fd as-is for read/write.
if (!write_exact(fd, &request_id, sizeof(request_id))) break; kj::Own<kj::AsyncIoStream> stream = io.lowLevelProvider->wrapSocketFd(fd);
if (!write_exact(fd, &byte_count, sizeof(byte_count))) break;
if (!write_exact(fd, &ok, sizeof(ok))) break; // Two-party RPC: the document process is the SERVER side (it serves the
// bootstrap capability the UI imports via getMain()).
capnp::TwoPartyVatNetwork network(*stream, capnp::rpc::twoparty::Side::SERVER);
auto server = capnp::makeRpcServer(network, kj::heap<DocumentProcessImpl>());
// Run the event loop until the UI process disconnects (onDisconnect
// resolves), then return cleanly.
auto disconnect = network.onDisconnect().then([]() {
std::fprintf(stderr, "[doc] UI disconnected\n");
});
try {
disconnect.wait(io.waitScope);
} catch (kj::Exception& e) {
std::fprintf(stderr, "[doc] event loop error: %s\n",
e.getDescription().cStr());
return 1;
} }
return 0; return 0;
} }

4
spike/E_sandbox/Sandbox.cpp
View File

@ -67,6 +67,10 @@ int install_sandbox()
allow_syscall(ctx, SCMP_SYS(timerfd_create)); allow_syscall(ctx, SCMP_SYS(timerfd_create));
allow_syscall(ctx, SCMP_SYS(timerfd_settime)); allow_syscall(ctx, SCMP_SYS(timerfd_settime));
allow_syscall(ctx, SCMP_SYS(dup)); // Cap'n Proto may dup its socket allow_syscall(ctx, SCMP_SYS(dup)); // Cap'n Proto may dup its socket
// ioctl(FIONBIO) is used by KJ's wrapSocketFd to set non-blocking mode on
// the socketpair end. Allow the syscall; FIONBIO is the only request the
// event loop issues on the IPC fd (no TCGETS/SG_ISPTTY etc. on a socket).
allow_syscall(ctx, SCMP_SYS(ioctl));
// Exit / signal. // Exit / signal.
allow_syscall(ctx, SCMP_SYS(exit)); allow_syscall(ctx, SCMP_SYS(exit));

119
spike/E_sandbox/UIProcess.cpp
View File

@ -1,12 +1,21 @@
// SPDX-License-Identifier: GPL-3.0-or-later // SPDX-License-Identifier: GPL-3.0-or-later
// SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors // SPDX-FileCopyrightText: 2025 ai-ad4 and the FreePDFEditor contributors
// //
// UIProcess.cpp — the UI process side. Drives the length-prefixed binary IPC // UIProcess.cpp — the UI process side. Drives the Cap'n Proto RPC channel,
// channel, sends Parse requests, and measures round-trip latency. The UI // sends Parse requests, and measures round-trip latency. The UI does no
// does no untrusted parsing; it validates the document process's responses // untrusted parsing; it validates the document process's responses (ADR-0004:
// (ADR-0004: bidirectional trust boundary). // bidirectional trust boundary).
//
// The client uses `EzRpcClient(int fd)`, which is designed for an
// already-connected socket (unlike EzRpcServer, which expects a listening
// socket). See DocumentProcess.cpp for the server-side integration note.
#include "UIProcess.h" #include "UIProcess.h"
#include "ipc.capnp.h"
#include <capnp/ez-rpc.h>
#include <capnp/message.h>
#include <kj/array.h>
#include <algorithm> #include <algorithm>
#include <chrono> #include <chrono>
@ -17,90 +26,70 @@
#include <vector> #include <vector>
#include <unistd.h> #include <unistd.h>
namespace proto = freepdfeditor::spike::e;
namespace freepdfeditor::spike::e { namespace freepdfeditor::spike::e {
namespace {
bool read_exact(int fd, void* buf, std::size_t n)
{
auto* p = static_cast<char*>(buf);
while (n > 0) {
ssize_t r = read(fd, p, n);
if (r <= 0) return false;
p += r; n -= std::size_t(r);
}
return true;
}
bool write_exact(int fd, const void* buf, std::size_t n)
{
const auto* p = static_cast<const char*>(buf);
while (n > 0) {
ssize_t w = write(fd, p, n);
if (w <= 0) return false;
p += w; n -= std::size_t(w);
}
return true;
}
} // namespace
UIResult run_ui_process(int parent_fd, int child_fd, UIResult run_ui_process(int parent_fd, int child_fd,
std::size_t n_requests, std::size_t payload_bytes) std::size_t n_requests, std::size_t payload_bytes)
{ {
(void)child_fd; // the child end is the document process's concern (void)child_fd; // the child end is the document process's concern
UIResult r{}; UIResult r{};
// The payload the UI hands the document process. Sent as a Cap'n Proto
// Data field; the document process counts the bytes and returns the count.
std::vector<unsigned char> payload(payload_bytes, 0xAB); std::vector<unsigned char> payload(payload_bytes, 0xAB);
// EzRpcClient(int fd) wraps an already-connected socket — exactly the
// socketpair-end shape. It sets up its own KJ EventLoop + WaitScope.
capnp::EzRpcClient client(parent_fd);
auto& waitScope = client.getWaitScope();
proto::DocumentProcess::Client doc =
client.getMain().castAs<proto::DocumentProcess>();
double min_us = 1e18, max_us = 0.0, sum_us = 0.0; double min_us = 1e18, max_us = 0.0, sum_us = 0.0;
std::size_t acked = 0; std::size_t acked = 0;
for (std::size_t i = 0; i < n_requests; ++i) { for (std::size_t i = 0; i < n_requests; ++i) {
auto t0 = std::chrono::steady_clock::now(); auto t0 = std::chrono::steady_clock::now();
// Request: [u64 request_id][u64 payload_len][payload] auto req = doc.parseRequest();
std::uint64_t request_id = static_cast<std::uint64_t>(i); req.getRequest().setRequestId(static_cast<std::uint64_t>(i));
std::uint64_t payload_len = static_cast<std::uint64_t>(payload_bytes); req.getRequest().setData(kj::ArrayPtr<const kj::byte>(
if (!write_exact(parent_fd, &request_id, sizeof(request_id))) { payload.data(), payload.size()));
r.error = "write request_id failed at " + std::to_string(i);
break;
}
if (!write_exact(parent_fd, &payload_len, sizeof(payload_len))) {
r.error = "write payload_len failed at " + std::to_string(i);
break;
}
if (!write_exact(parent_fd, payload.data(), payload_bytes)) {
r.error = "write payload failed at " + std::to_string(i);
break;
}
// Response: [u64 request_id][u64 byte_count][u8 ok] // The Response owns the message backing the result reader, so it must
std::uint64_t resp_id = 0, byte_count = 0; // stay alive for as long as we read from `resp` (a dangling reader is
std::uint8_t ok = 0; // a use-after-free — ASan catches it, validating §7.2). Validate the
if (!read_exact(parent_fd, &resp_id, sizeof(resp_id))) { // response inside the scope that owns the Response.
r.error = "read resp_id failed at " + std::to_string(i); bool ok = false;
break; std::string err;
std::uint64_t resp_id = 0;
std::uint64_t byte_count = 0;
try {
auto response = req.send().wait(waitScope);
auto resp = response.getResult();
ok = resp.getOk();
if (!ok) {
err = "doc returned ok=false: " + std::string(resp.getError().cStr());
} else {
resp_id = resp.getRequestId();
byte_count = resp.getByteCount();
} }
if (!read_exact(parent_fd, &byte_count, sizeof(byte_count))) { } catch (kj::Exception& e) {
r.error = "read byte_count failed at " + std::to_string(i); err = "RPC failed: " + std::string(e.getDescription().cStr());
break;
}
if (!read_exact(parent_fd, &ok, sizeof(ok))) {
r.error = "read ok failed at " + std::to_string(i);
break;
} }
auto t1 = std::chrono::steady_clock::now(); auto t1 = std::chrono::steady_clock::now();
double us = std::chrono::duration<double, std::micro>(t1 - t0).count(); double us = std::chrono::duration<double, std::micro>(t1 - t0).count();
sum_us += us;
min_us = std::min(min_us, us);
max_us = std::max(max_us, us);
// Validate the response (ADR-0004: the IPC is a trust boundary in both // Validate the response (ADR-0004: the IPC is a trust boundary in both
// directions — the UI never trusts the document process blindly). // directions — the UI never trusts the document process blindly).
if (!ok) { r.error = "doc returned ok=false at " + std::to_string(i); break; } if (!ok) {
if (resp_id != request_id) { r.error = err + " at " + std::to_string(i);
break;
}
if (resp_id != static_cast<std::uint64_t>(i)) {
r.error = "request id mismatch at " + std::to_string(i); r.error = "request id mismatch at " + std::to_string(i);
break; break;
} }
@ -110,6 +99,10 @@ UIResult run_ui_process(int parent_fd, int child_fd,
" expected " + std::to_string(payload_bytes); " expected " + std::to_string(payload_bytes);
break; break;
} }
sum_us += us;
min_us = std::min(min_us, us);
max_us = std::max(max_us, us);
++acked; ++acked;
} }

5
spike/E_sandbox/main.cpp
View File

@ -82,7 +82,7 @@ int main(int argc, char** argv)
freepdfeditor::spike::SpikeResult sr{}; freepdfeditor::spike::SpikeResult sr{};
sr.spike = "E"; sr.spike = "E";
sr.name = "sandbox + IPC bring-up (seccomp-bpf, length-prefixed socketpair)"; sr.name = "sandbox + IPC bring-up (seccomp-bpf, Cap'n Proto two-party RPC over socketpair)";
sr.total = n_requests; sr.total = n_requests;
sr.passed = r.requests_acked; sr.passed = r.requests_acked;
sr.failed = n_requests - r.requests_acked; sr.failed = n_requests - r.requests_acked;
@ -96,7 +96,8 @@ int main(int argc, char** argv)
"requests=%zu acked=%zu payload=%zuB " "requests=%zu acked=%zu payload=%zuB "
"avg_latency=%.1fus min=%.1fus max=%.1fus wall=%.1fus " "avg_latency=%.1fus min=%.1fus max=%.1fus wall=%.1fus "
"child_exit=%d; seccomp-bpf deny=open/socket/connect/fork/exec, " "child_exit=%d; seccomp-bpf deny=open/socket/connect/fork/exec, "
"allow=memory/read/write/poll/epoll/exit", "allow=memory/read/write/poll/epoll/ioctl/exit; "
"transport=Cap'n Proto two-party RPC (wrapSocketFd + TwoPartyVatNetwork)",
n_requests, r.requests_acked, payload_bytes, n_requests, r.requests_acked, payload_bytes,
r.avg_latency_us, r.min_latency_us, r.max_latency_us, wall_us, r.avg_latency_us, r.min_latency_us, r.max_latency_us, wall_us,
WIFEXITED(status) ? WEXITSTATUS(status) : -1); WIFEXITED(status) ? WEXITSTATUS(status) : -1);