macOS prototype

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
     strategy:
       fail-fast: ${{ github.event_name == 'merge_group' }}
       matrix:
-        environment: [ubuntu-latest]
+        environment: [ubuntu-latest, macos-latest]
 
     runs-on: ${{ matrix.environment }}
 
@@ -71,11 +71,14 @@ jobs:
 
       - name: Install tools
         run: |
-          sudo apt install bubblewrap
           rustup install nightly
           rustup +nightly component add clippy
           cargo install group-runner || true
 
+      - name: Install Bubblewrap
+        if: ${{ matrix.environment == 'ubuntu-latest' }}
+        run: sudo apt install bubblewrap
+
       - name: Build
         run: cargo test --no-run
 

README.md

@@ -2,7 +2,7 @@
 
 A linker replacement to help protect against malicious build scripts
 
-`build-wrap` "re-links" a build script so that it is executed under another command. By default the command is [Bubblewrap], though this is configurable. See [Environment variables] and [How it works] for more information.
+`build-wrap` "re-links" a build script so that it is executed under another command. By default, the command is [Bubblewrap] (Linux) or [`sandbox-exec`] (macOS), though this is configurable. See [Environment variables] and [How it works] for more information.
 
 ## Installation
 
@@ -20,7 +20,7 @@ Installing `build-wrap` requires two steps:
 
 ## Environment variables
 
-- `BUILD_WRAP_CMD`: Command used to execute a build script. Default:
+- `BUILD_WRAP_CMD`: Command used to execute a build script. Linux default:
 
   ```sh
   bwrap
@@ -34,6 +34,25 @@ Installing `build-wrap` requires two steps:
 
   Note that `bwrap` is [Bubblewrap].
 
+  macOS default:
+
+  ```sh
+  sandbox-exec -p
+  (version\ 1)\
+  (deny\ default)\
+  (allow\ file-read*)\                          # Allow read-only access everywhere
+  (allow\ file-write*\ (subpath\ "/dev"))\      # Allow write access to /dev
+  (allow\ file-write*\ (subpath\ "{OUT_DIR}"))\ # Allow write access to `OUT_DIR`
+  (allow\ file-write*\ (subpath\ "{TMPDIR}"))\  # Allow write access to `TMPDIR`
+  (allow\ process-exec)\                        # Allow `exec`
+  (allow\ process-fork)\                        # Allow `fork`
+  (allow\ sysctl-read)\                         # Allow reading kernel state
+  (deny\ network*)                              # Deny network access
+  {}                                            # Build script path
+  ```
+
+  Note that `(version\ 1)\ ... (deny\ network*)` expands to a single string (see [How `BUILD_WRAP_CMD` is expanded] below).
+
 - `BUILD_WRAP_LD`: Linker to use. Default: `cc`
 
 Note that the above environment variables are read **when the build script is linked**. So, for example, changing `BUILD_WRAP_CMD` will not change the command used to execute already linked build scripts.
@@ -65,4 +84,6 @@ Given a build script `B`, its "wrapped" version `B'` contains a copy of `B` and
 [Bubblewrap]: https://github.com/containers/bubblewrap
 [Environment variables]: #environment-variables
 [How it works]: #how-it-works
+[How `BUILD_WRAP_CMD` is expanded]: #how-build_wrap_cmd-is-expanded
+[`sandbox-exec`]: https://keith.github.io/xcode-man-pages/sandbox-exec.1.html
 [manner described above]: #how-build_wrap_cmd-is-expanded

src/main.rs

@@ -10,13 +10,38 @@ use std::{
 mod util;
 mod wrapper;
 
-const DEFAULT_CMD: &str = "bwrap
+const DEFAULT_CMD: &str = if cfg!(target_os = "linux") {
+    "bwrap
     --ro-bind / /
     --dev-bind /dev /dev
     --bind {OUT_DIR} {OUT_DIR}
     --bind /tmp /tmp
     --unshare-net
-    {}";
+    {}"
+} else {
+    // smoelius: The following blog post is a useful `sandbox-exec` reference:
+    // https://7402.org/blog/2020/macos-sandboxing-of-folder.html
+    // smoelius: The following package does not build with the current `sandbox-exec` command:
+    // https://crates.io/crates/psm
+    // Adding the following line fixes the problem:
+    // ```
+    // (allow\ file-write*\ (subpath\ "/private{TMPDIR}"))\
+    // ```
+    // However, I don't want to pollute the command for this one package. This issue requires
+    // further investigation.
+    r#"sandbox-exec -p
+(version\ 1)\
+(deny\ default)\
+(allow\ file-read*)\
+(allow\ file-write*\ (subpath\ "/dev"))\
+(allow\ file-write*\ (subpath\ "{OUT_DIR}"))\
+(allow\ file-write*\ (subpath\ "{TMPDIR}"))\
+(allow\ process-exec)\
+(allow\ process-fork)\
+(allow\ sysctl-read)\
+(deny\ network*)
+{}"#
+};
 
 fn main() -> Result<()> {
     let args: Vec<String> = args().collect();

tests/cases/outside_out_dir.macos.stderr

@@ -0,0 +1 @@
+message: "Operation not permitted"

tests/cases/ping.macos.stderr

@@ -0,0 +1 @@
+ping: sendto: Operation not permitted

tests/cases/tiocsti.macos.stderr

@@ -0,0 +1 @@
+libc::ioctl: Operation not permitted

tests/custom_build_name.rs

@@ -20,8 +20,13 @@ fn custom_build_name() {
     assert!(!output.status.success());
 
     let stderr = std::str::from_utf8(&output.stderr).unwrap();
+    let syscall = if cfg!(target_os = "linux") {
+        "socket"
+    } else {
+        "sendto"
+    };
     assert!(
-        stderr.contains("ping: socket: Operation not permitted"),
+        stderr.contains(&format!("ping: {syscall}: Operation not permitted")),
         "stderr does not contain expected string:\n```\n{stderr}\n```",
     );
 }

tests/integration.rs

@@ -36,7 +36,14 @@ fn integration() {
 }
 
 fn test_case(path: &Path) {
-    let stderr_path = path.with_extension("stderr");
+    let mut stderr_path = path.with_extension("stderr");
+    if !stderr_path.exists() {
+        stderr_path = if cfg!(target_os = "linux") {
+            path.with_extension("linux.stderr")
+        } else {
+            path.with_extension("macos.stderr")
+        }
+    }
     let expected_stderr_substring = read_to_string(stderr_path).unwrap();
 
     let temp_package = util::temp_package(path).unwrap();