bpf loader - finish support for kernel version conditional loading

bpf program section names must be unique to prevent programs from
appending to each other, so instead the bpf loader will strip
everything past the final $ symbol when actually pinning
the program into the filesystem.

While at it add a little bit more logging.

Example on aosp cuttlefish 5.4.30 virtual device:
  D LibBpfLoader: bpf_prog_load lib call for /system/etc/bpf/offload.o (schedcls_ingress_tether_ether) returned fd: 8 (no error)
  D LibBpfLoader: cs[1].name:schedcls_ingress_tether_rawip$stub min_kver:0 .max_kver:40e00 (kvers:5041e)
  D LibBpfLoader: cs[2].name:schedcls_ingress_tether_rawip$4_14 min_kver:40e00 .max_kver:ffffffff (kvers:5041e)
  D LibBpfLoader: bpf_prog_load lib call for /system/etc/bpf/offload.o (schedcls_ingress_tether_rawip$4_14) returned fd: 9 (no error)
  I bpfloader: Attempted load object: /system/etc/bpf/offload.o, ret: Success

  $ adb shell ls -l /sys/fs/bpf | egrep offload
  -rw-rw---- 1 root network_stack 0 2020-04-22 01:27 map_offload_tether_ingress_map
  -rw-rw---- 1 root network_stack 0 2020-04-22 01:27 map_offload_tether_stats_map
  -r--r----- 1 root root          0 2020-04-22 01:27 prog_offload_schedcls_ingress_tether_ether
  -r--r----- 1 root root          0 2020-04-22 01:27 prog_offload_schedcls_ingress_tether_rawip

Test: builds, atest, proper program loaded on 5.4.30 aosp cuttlefish
Bug: 149434314
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Id3fcb8e2a6b0087f704e77726e9961efc6145739
Merged-In: Id3fcb8e2a6b0087f704e77726e9961efc6145739

1 files changed, 18 insertions, 9 deletions

diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp
index ce710a4..d2a502d 100644
--- a/libbpf_android/Loader.cpp
+++ b/libbpf_android/Loader.cpp
@@ -540,27 +540,36 @@ static int loadCodeSections(const char* elfPath, vector<codeSection>& cs, const
     string fname = pathToFilename(string(elfPath), true);
 
     for (int i = 0; i < (int)cs.size(); i++) {
-        string progPinLoc;
-        bool reuse = false;
+        string name = cs[i].name;
 
         if (cs[i].prog_def.has_value()) {
-            if (kvers < cs[i].prog_def->min_kver) continue;
-            if (kvers >= cs[i].prog_def->max_kver) continue;
+            unsigned min_kver = cs[i].prog_def->min_kver;
+            unsigned max_kver = cs[i].prog_def->max_kver;
+            ALOGD("cs[%d].name:%s min_kver:%x .max_kver:%x (kvers:%x)\n", i, name.c_str(), min_kver,
+                  max_kver, kvers);
+            if (kvers < min_kver) continue;
+            if (kvers >= max_kver) continue;
         }
 
+        // strip any potential $foo suffix
+        // this can be used to provide duplicate programs
+        // conditionally loaded based on running kernel version
+        name = name.substr(0, name.find_last_of("$"));
+
+        bool reuse = false;
         // Format of pin location is
         // /sys/fs/bpf/prog_<filename>_<mapname>
-        progPinLoc = string(BPF_FS_PATH) + "prog_" + fname + "_" + cs[i].name;
+        string progPinLoc = string(BPF_FS_PATH) + "prog_" + fname + "_" + name;
         if (access(progPinLoc.c_str(), F_OK) == 0) {
             fd = bpf_obj_get(progPinLoc.c_str());
-            ALOGD("New bpf prog load reusing prog %s, ret: %d\n", cs[i].name.c_str(), fd);
+            ALOGD("New bpf prog load reusing prog %s, ret: %d\n", progPinLoc.c_str(), fd);
             reuse = true;
         } else {
             vector<char> log_buf(BPF_LOAD_LOG_SZ, 0);
 
-            fd = bpf_prog_load(cs[i].type, cs[i].name.c_str(), (struct bpf_insn*)cs[i].data.data(),
-                               cs[i].data.size(), license.c_str(), kvers, 0,
-                               log_buf.data(), log_buf.size());
+            fd = bpf_prog_load(cs[i].type, name.c_str(), (struct bpf_insn*)cs[i].data.data(),
+                               cs[i].data.size(), license.c_str(), kvers, 0, log_buf.data(),
+                               log_buf.size());
             ALOGD("bpf_prog_load lib call for %s (%s) returned fd: %d (%s)\n", elfPath,
                   cs[i].name.c_str(), fd, (fd < 0 ? std::strerror(errno) : "no error"));