crash_dump: during early boot, output to kmsg on userdebug.

am: 3e76ecaf80

Change-Id: I72baab899157ebc2e0379e0bd2a46d61c6f5ed8f

debuggerd/libdebuggerd/utility.cpp

@@ -22,16 +22,22 @@
 #include <signal.h>
 #include <string.h>
 #include <sys/ptrace.h>
+#include <sys/uio.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
 #include <string>
 
+#include <android-base/logging.h>
+#include <android-base/properties.h>
 #include <android-base/stringprintf.h>
+#include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <backtrace/Backtrace.h>
 #include <log/log.h>
 
+using android::base::unique_fd;
+
 // Whitelist output desired in the logcat output.
 bool is_allowed_in_logcat(enum logtype ltype) {
   if ((ltype == HEADER)
@@ -42,6 +48,19 @@ bool is_allowed_in_logcat(enum logtype ltype) {
   return false;
 }
 
+static bool should_write_to_kmsg() {
+  // Write to kmsg if tombstoned isn't up, and we're able to do so.
+  if (!android::base::GetBoolProperty("ro.debuggable", false)) {
+    return false;
+  }
+
+  if (android::base::GetProperty("init.svc.tombstoned", "") == "running") {
+    return false;
+  }
+
+  return true;
+}
+
 __attribute__((__weak__, visibility("default")))
 void _LOG(log_t* log, enum logtype ltype, const char* fmt, ...) {
   bool write_to_tombstone = (log->tfd != -1);
@@ -49,6 +68,7 @@ void _LOG(log_t* log, enum logtype ltype, const char* fmt, ...) {
                       && log->crashed_tid != -1
                       && log->current_tid != -1
                       && (log->crashed_tid == log->current_tid);
+  static bool write_to_kmsg = should_write_to_kmsg();
 
   char buf[512];
   va_list ap;
@@ -70,6 +90,30 @@ void _LOG(log_t* log, enum logtype ltype, const char* fmt, ...) {
     if (log->amfd_data != nullptr) {
       *log->amfd_data += buf;
     }
+
+    if (write_to_kmsg) {
+      unique_fd kmsg_fd(open("/dev/kmsg_debug", O_WRONLY | O_APPEND | O_CLOEXEC));
+      if (kmsg_fd.get() >= 0) {
+        // Our output might contain newlines which would otherwise be handled by the android logger.
+        // Split the lines up ourselves before sending to the kernel logger.
+        if (buf[len - 1] == '\n') {
+          buf[len - 1] = '\0';
+        }
+
+        std::vector<std::string> fragments = android::base::Split(buf, "\n");
+        for (const std::string& fragment : fragments) {
+          static constexpr char prefix[] = "<3>DEBUG: ";
+          struct iovec iov[3];
+          iov[0].iov_base = const_cast<char*>(prefix);
+          iov[0].iov_len = strlen(prefix);
+          iov[1].iov_base = const_cast<char*>(fragment.c_str());
+          iov[1].iov_len = fragment.length();
+          iov[2].iov_base = const_cast<char*>("\n");
+          iov[2].iov_len = 1;
+          TEMP_FAILURE_RETRY(writev(kmsg_fd.get(), iov, 3));
+        }
+      }
+    }
   }
 }
 
@@ -205,7 +249,7 @@ void dump_memory(log_t* log, Backtrace* backtrace, uintptr_t addr, const char* f
 }
 
 void read_with_default(const char* path, char* buf, size_t len, const char* default_value) {
-  android::base::unique_fd fd(open(path, O_RDONLY));
+  unique_fd fd(open(path, O_RDONLY | O_CLOEXEC));
   if (fd != -1) {
     int rc = TEMP_FAILURE_RETRY(read(fd.get(), buf, len - 1));
     if (rc != -1) {

init/Android.mk

@@ -9,12 +9,14 @@ init_options += \
     -DALLOW_LOCAL_PROP_OVERRIDE=1 \
     -DALLOW_PERMISSIVE_SELINUX=1 \
     -DREBOOT_BOOTLOADER_ON_PANIC=1 \
+    -DWORLD_WRITABLE_KMSG=1 \
     -DDUMP_ON_UMOUNT_FAILURE=1
 else
 init_options += \
     -DALLOW_LOCAL_PROP_OVERRIDE=0 \
     -DALLOW_PERMISSIVE_SELINUX=0 \
     -DREBOOT_BOOTLOADER_ON_PANIC=0 \
+    -DWORLD_WRITABLE_KMSG=0 \
     -DDUMP_ON_UMOUNT_FAILURE=0
 endif
 

init/init.cpp

@@ -933,6 +933,9 @@ static void selinux_restore_context() {
     LOG(INFO) << "Running restorecon...";
     selinux_android_restorecon("/dev", 0);
     selinux_android_restorecon("/dev/kmsg", 0);
+    if constexpr (WORLD_WRITABLE_KMSG) {
+        selinux_android_restorecon("/dev/kmsg_debug", 0);
+    }
     selinux_android_restorecon("/dev/socket", 0);
     selinux_android_restorecon("/dev/random", 0);
     selinux_android_restorecon("/dev/urandom", 0);
@@ -1036,7 +1039,13 @@ int main(int argc, char** argv) {
         setgroups(arraysize(groups), groups);
         mount("sysfs", "/sys", "sysfs", 0, NULL);
         mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);
+
         mknod("/dev/kmsg", S_IFCHR | 0600, makedev(1, 11));
+
+        if constexpr (WORLD_WRITABLE_KMSG) {
+            mknod("/dev/kmsg_debug", S_IFCHR | 0622, makedev(1, 11));
+        }
+
         mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));
         mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));