From 0b477491fb95c04d908ef83d683c42db9102cf40 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= <maze@google.com>
Date: Tue, 4 Mar 2025 22:12:42 -0800
Subject: [PATCH] bpf: switch to mainline netbpfload on Android S/SV2
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Test: TreeHugger, manually installing tethering apex
  (with and without dnsresolver apex) on pixel 6 running S
  incl. 'atest bpf_existence_test'
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I63d4b84287e9c98dc0d2a517ac58d3f3ce9d7760
---
 Tethering/apex/Android.bp            |  3 +-
 bpf/dns_helper/DnsBpfHelper.cpp      | 36 ++++++++++++++++++++--
 bpf/loader/Android.bp                | 13 +++++++-
 bpf/loader/NetBpfLoad.cpp            | 46 +++++++++++++++++++---------
 bpf/loader/netbpfload.31rc           | 13 ++++++++
 bpf/progs/Android.bp                 | 20 ++----------
 bpf/progs/offload.c                  | 12 ++------
 bpf/progs/test.c                     | 12 ++------
 bpf/tests/mts/bpf_existence_test.cpp |  7 ++++-
 9 files changed, 103 insertions(+), 59 deletions(-)
 create mode 100644 bpf/loader/netbpfload.31rc

diff --git a/Tethering/apex/Android.bp b/Tethering/apex/Android.bp
index 19dd492b67..2878f79458 100644
--- a/Tethering/apex/Android.bp
+++ b/Tethering/apex/Android.bp
@@ -102,15 +102,14 @@ apex {
         "dscpPolicy.o",
         "netd.o",
         "offload.o",
-        "offload@mainline.o",
         "test.o",
-        "test@mainline.o",
     ],
     apps: [
         "ServiceConnectivityResources",
     ],
     prebuilts: [
         "current_sdkinfo",
+        "netbpfload.31rc",
         "netbpfload.33rc",
         "netbpfload.35rc",
         "ot-daemon.34rc",
diff --git a/bpf/dns_helper/DnsBpfHelper.cpp b/bpf/dns_helper/DnsBpfHelper.cpp
index 0719ade395..cf2fa2b736 100644
--- a/bpf/dns_helper/DnsBpfHelper.cpp
+++ b/bpf/dns_helper/DnsBpfHelper.cpp
@@ -32,12 +32,44 @@ namespace net {
     }                                                                                              \
   } while (0)
 
+// copied from BpfHandler.cpp
+static bool mainlineNetBpfLoadDone() {
+  return !access("/sys/fs/bpf/netd_shared/mainline_done", F_OK);
+}
+
+// copied from BpfHandler.cpp
+static inline void waitForNetProgsLoaded() {
+  // infinite loop until success with 5/10/20/40/60/60/60... delay
+  for (int delay = 5;; delay *= 2) {
+    if (delay > 60) delay = 60;
+    if (base::WaitForProperty("init.svc.mdnsd_netbpfload", "stopped", std::chrono::seconds(delay))
+      && mainlineNetBpfLoadDone()) return;
+    LOG(WARNING) << "Waited " << delay << "s for init.svc.mdnsd_netbpfload=stopped, still waiting.";
+  }
+}
+
 base::Result<void> DnsBpfHelper::init() {
-  if (!android::modules::sdklevel::IsAtLeastT()) {
-    LOG(ERROR) << __func__ << ": Unsupported before Android T.";
+  if (!android::modules::sdklevel::IsAtLeastS()) {
+    LOG(ERROR) << __func__ << ": Unsupported before Android S.";
     return base::Error(EOPNOTSUPP);
   }
 
+  if (!android::modules::sdklevel::IsAtLeastT()) {
+    LOG(INFO) << "performing Android S mainline NetBpfload magic!";
+    if (!mainlineNetBpfLoadDone()) {
+      // We're on S/Sv2 & it's the first time netd is starting up (unless crashlooping)
+      if (!base::SetProperty("ctl.start", "mdnsd_netbpfload")) {
+        LOG(ERROR) << "Failed to set property ctl.start=mdnsd_netbpfload, see dmesg for reason.";
+        return base::Error(ENOEXEC);
+      }
+
+      LOG(INFO) << "Waiting for Networking BPF programs";
+      waitForNetProgsLoaded();
+      LOG(INFO) << "Networking BPF programs are loaded";
+    }
+    return {};
+  }
+
   RETURN_IF_RESULT_NOT_OK(mConfigurationMap.init(CONFIGURATION_MAP_PATH));
   RETURN_IF_RESULT_NOT_OK(mUidOwnerMap.init(UID_OWNER_MAP_PATH));
   RETURN_IF_RESULT_NOT_OK(mDataSaverEnabledMap.init(DATA_SAVER_ENABLED_MAP_PATH));
diff --git a/bpf/loader/Android.bp b/bpf/loader/Android.bp
index b08913a2c5..780fe20d84 100644
--- a/bpf/loader/Android.bp
+++ b/bpf/loader/Android.bp
@@ -56,11 +56,22 @@ cc_binary {
     installable: false,
 }
 
-// Versioned netbpfload init rc: init system will process it only on api T/33+ devices
+// Versioned netbpfload init rc: init system will process it only on api R/30 S/31 Sv2/32 devices
 // Note: R[30] S[31] Sv2[32] T[33] U[34] V[35])
 //
 // For details of versioned rc files see:
 // https://android.googlesource.com/platform/system/core/+/HEAD/init/README.md#versioned-rc-files-within-apexs
+//
+// However, .Xrc versioning doesn't work on S, so we use unversioned, and thus *do* trigger on R,
+// luckily nothing ever uses the new service on R, so you can think of it as being S/Sv2 only
+prebuilt_etc {
+    name: "netbpfload.31rc",
+    src: "netbpfload.31rc",
+    filename: "netbpfload.rc", // intentional: .31rc wouldn't take effect on S
+    installable: false,
+}
+
+// Versioned netbpfload init rc: init system will process it only on api T/33+ devices
 prebuilt_etc {
     name: "netbpfload.33rc",
     src: "netbpfload.33rc",
diff --git a/bpf/loader/NetBpfLoad.cpp b/bpf/loader/NetBpfLoad.cpp
index 9c62e7440f..bad506f7c0 100644
--- a/bpf/loader/NetBpfLoad.cpp
+++ b/bpf/loader/NetBpfLoad.cpp
@@ -122,6 +122,7 @@ static constexpr bool specified(domain d) {
 struct Location {
     const char* const dir = "";
     const char* const prefix = "";
+    const bool t_plus = true;
 };
 
 // Returns the build type string (from ro.build.type).
@@ -1216,8 +1217,9 @@ static bool exists(const char* const path) {
 const Location locations[] = {
         // S+ Tethering mainline module (network_stack): tether offload
         {
-                .dir = BPFROOT "/",
+                .dir = BPFROOT "/tethering/",
                 .prefix = "tethering/",
+                .t_plus = false,
         },
         // T+ Tethering mainline module (shared with netd & system server)
         // netutils_wrapper (for iptables xt_bpf) has access to programs
@@ -1412,6 +1414,13 @@ static bool isWear() {
 }
 
 static int doLoad(char** argv, char * const envp[]) {
+    if (!isAtLeastS) {
+        ALOGE("Impossible - not reachable on Android <S.");
+        // for safety, we don't fail, this is a just-in-case workaround
+        // for any possible busted 'optimized' start everything vendor init hacks on R
+        return 0;
+    }
+
     const bool runningAsRoot = !getuid();  // true iff U QPR3 or V+
 
     const int first_api_level = GetIntProperty("ro.board.first_api_level", api_level);
@@ -1446,14 +1455,9 @@ static int doLoad(char** argv, char * const envp[]) {
 
     logTetheringApexVersion();
 
-    if (!isAtLeastT) {
-        ALOGE("Impossible - not reachable on Android <T.");
-        return 1;
-    }
-
     // both S and T require kernel 4.9 (and eBpf support)
-    if (isAtLeastT && !isAtLeastKernelVersion(4, 9, 0)) {
-        ALOGE("Android T requires kernel 4.9.");
+    if (!isAtLeastKernelVersion(4, 9, 0)) {
+        ALOGE("Android S & T require kernel 4.9.");
         return 1;
     }
 
@@ -1622,18 +1626,22 @@ static int doLoad(char** argv, char * const envp[]) {
     //  which could otherwise fail with ENOENT during object pinning or renaming,
     //  due to ordering issues)
     for (const auto& location : locations) {
+        if (location.t_plus && !isAtLeastT) continue;
         if (createSysFsBpfSubDir(location.prefix)) return 1;
     }
 
-    // Note: there's no actual src dir for fs_bpf_loader .o's,
-    // so it is not listed in 'locations[].prefix'.
-    // This is because this is primarily meant for triggering genfscon rules,
-    // and as such this will likely always be the case.
-    // Thus we need to manually create the /sys/fs/bpf/loader subdirectory.
-    if (createSysFsBpfSubDir("loader")) return 1;
+    if (isAtLeastT) {
+        // Note: there's no actual src dir for fs_bpf_loader .o's,
+        // so it is not listed in 'locations[].prefix'.
+        // This is because this is primarily meant for triggering genfscon rules,
+        // and as such this will likely always be the case.
+        // Thus we need to manually create the /sys/fs/bpf/loader subdirectory.
+        if (createSysFsBpfSubDir("loader")) return 1;
+    }
 
     // Load all ELF objects, create programs and maps, and pin them
     for (const auto& location : locations) {
+        if (location.t_plus && !isAtLeastT) continue;
         if (loadAllElfObjects(bpfloader_ver, location) != 0) {
             ALOGE("=== CRITICAL FAILURE LOADING BPF PROGRAMS FROM %s ===", location.dir);
             ALOGE("If this triggers reliably, you're probably missing kernel options or patches.");
@@ -1654,6 +1662,9 @@ static int doLoad(char** argv, char * const envp[]) {
         return 1;
     }
 
+    // on S we haven't created this subdir yet, but we need it for 'mainline_done' flag below
+    if (!isAtLeastT && createSysFsBpfSubDir("netd_shared")) return 1;
+
     // leave a flag that we're done
     if (createSysFsBpfSubDir("netd_shared/mainline_done")) return 1;
 
@@ -1688,7 +1699,12 @@ static int doLoad(char** argv, char * const envp[]) {
 }  // namespace android
 
 int main(int argc, char** argv, char * const envp[]) {
-    InitLogging(argv, &KernelLogger);
+    if (android::bpf::isAtLeastT) {
+        InitLogging(argv, &KernelLogger);
+    } else {
+        // S lacks the sepolicy to make non-root uid KernelLogger viable
+        InitLogging(argv);
+    }
 
     if (argc == 2 && !strcmp(argv[1], "done")) {
         // we're being re-exec'ed from platform bpfloader to 'finalize' things
diff --git a/bpf/loader/netbpfload.31rc b/bpf/loader/netbpfload.31rc
new file mode 100644
index 0000000000..bca7dc84d3
--- /dev/null
+++ b/bpf/loader/netbpfload.31rc
@@ -0,0 +1,13 @@
+# This file takes effect only on S and Sv2
+# (Note: it does take effect on R as well, but isn't actually used)
+#
+# The service is started from netd's dnsresolver call into ADnsHelper_init()
+# on initial (boot time) startup of netd.
+
+service mdnsd_netbpfload /apex/com.android.tethering/bin/netbpfload
+    capabilities CHOWN SYS_ADMIN NET_ADMIN
+    group system root graphics network_stack net_admin net_bw_acct net_bw_stats net_raw
+    user system
+    rlimit memlock 1073741824 1073741824
+    oneshot
+    reboot_on_failure reboot,netbpfload-failed
diff --git a/bpf/progs/Android.bp b/bpf/progs/Android.bp
index 20d194c5ab..2bfe613bb0 100644
--- a/bpf/progs/Android.bp
+++ b/bpf/progs/Android.bp
@@ -69,32 +69,16 @@ bpf {
     sub_dir: "net_shared",
 }
 
-// Ships to Android S, the bpfloader of which fails to parse BTF enabled .o's.
 bpf {
     name: "offload.o",
     srcs: ["offload.c"],
-    btf: false,
+    sub_dir: "tethering",
 }
 
-// This version ships to Android T+ which uses mainline netbpfload.
-bpf {
-    name: "offload@mainline.o",
-    srcs: ["offload@mainline.c"],
-    cflags: ["-DMAINLINE"],
-}
-
-// Ships to Android S, the bpfloader of which fails to parse BTF enabled .o's.
 bpf {
     name: "test.o",
     srcs: ["test.c"],
-    btf: false,
-}
-
-// This version ships to Android T+ which uses mainline netbpfload.
-bpf {
-    name: "test@mainline.o",
-    srcs: ["test@mainline.c"],
-    cflags: ["-DMAINLINE"],
+    sub_dir: "tethering",
 }
 
 bpf {
diff --git a/bpf/progs/offload.c b/bpf/progs/offload.c
index 0f23844f76..b34fe6fd88 100644
--- a/bpf/progs/offload.c
+++ b/bpf/progs/offload.c
@@ -14,16 +14,8 @@
  * limitations under the License.
  */
 
-#ifdef MAINLINE
-// BTF is incompatible with bpfloaders < v0.10, hence for S (v0.2) we must
-// ship a different file than for later versions, but we need bpfloader v0.25+
-// for obj@ver.o support
-#define BPFLOADER_MIN_VER BPFLOADER_MAINLINE_T_VERSION
-#else /* MAINLINE */
-// The resulting .o needs to load on the Android S bpfloader
-#define BPFLOADER_MIN_VER BPFLOADER_S_VERSION
-#define BPFLOADER_MAX_VER BPFLOADER_T_VERSION
-#endif /* MAINLINE */
+// The resulting .o needs to load on Android S+
+#define BPFLOADER_MIN_VER BPFLOADER_MAINLINE_S_VERSION
 
 #include "bpf_net_helpers.h"
 #include "offload.h"
diff --git a/bpf/progs/test.c b/bpf/progs/test.c
index 8585118bca..4dba6b9878 100644
--- a/bpf/progs/test.c
+++ b/bpf/progs/test.c
@@ -14,16 +14,8 @@
  * limitations under the License.
  */
 
-#ifdef MAINLINE
-// BTF is incompatible with bpfloaders < v0.10, hence for S (v0.2) we must
-// ship a different file than for later versions, but we need bpfloader v0.25+
-// for obj@ver.o support
-#define BPFLOADER_MIN_VER BPFLOADER_MAINLINE_T_VERSION
-#else /* MAINLINE */
-// The resulting .o needs to load on the Android S bpfloader
-#define BPFLOADER_MIN_VER BPFLOADER_S_VERSION
-#define BPFLOADER_MAX_VER BPFLOADER_T_VERSION
-#endif /* MAINLINE */
+// The resulting .o needs to load on Android S+
+#define BPFLOADER_MIN_VER BPFLOADER_MAINLINE_S_VERSION
 
 // This is non production code, only used for testing
 // Needed because the bitmap array definition is non-kosher for pre-T OS devices.
diff --git a/bpf/tests/mts/bpf_existence_test.cpp b/bpf/tests/mts/bpf_existence_test.cpp
index 75fb8e9f8c..4d5f9b54c7 100644
--- a/bpf/tests/mts/bpf_existence_test.cpp
+++ b/bpf/tests/mts/bpf_existence_test.cpp
@@ -196,7 +196,12 @@ TEST_F(BpfExistenceTest, TestPrograms) {
 
     // S requires Linux Kernel 4.9+ and thus requires eBPF support.
     if (isAtLeastS) ASSERT_TRUE(isAtLeastKernelVersion(4, 9, 0));
-    DO_EXPECT(isAtLeastS, MAINLINE_FOR_S_PLUS);
+
+    // on S without a new enough DnsResolver apex, NetBpfLoad doesn't get triggered,
+    // and thus no mainline programs get loaded.
+    bool mainlineBpfCapableResolve = !access("/apex/com.android.resolv/NetBpfLoad-S.flag", F_OK);
+    bool mainlineNetBpfLoad = isAtLeastT || mainlineBpfCapableResolve;
+    DO_EXPECT(isAtLeastS && mainlineNetBpfLoad, MAINLINE_FOR_S_PLUS);
 
     // Nothing added or removed in SCv2.