simpleperf: check kernel symbol addresses before dumping them.

If kernel symbols have zero addresses, there is no need to dump them,
and we can give useful suggestion.

Bug: 29574526
Test: manually set /proc/sys/kernel/kptr_restrict and run simpleperf record.
Change-Id: I850531c7e4c5315a44e08cf3b73852e77fef8eb8

3 files changed, 27 insertions, 1 deletions

diff --git a/simpleperf/cmd_record.cpp b/simpleperf/cmd_record.cpp
index a7988173..1d283fc0 100644
--- a/simpleperf/cmd_record.cpp
+++ b/simpleperf/cmd_record.cpp
@@ -643,7 +643,7 @@ bool RecordCommand::DumpKernelSymbol() {
         }
       }
     }
-    if (need_kernel_symbol) {
+    if (need_kernel_symbol && CheckKernelSymbolAddresses()) {
       if (!android::base::ReadFileToString("/proc/kallsyms", &kallsyms)) {
         PLOG(ERROR) << "failed to read /proc/kallsyms";
         return false;
diff --git a/simpleperf/environment.cpp b/simpleperf/environment.cpp
index 0024f961..f0203cfe 100644
--- a/simpleperf/environment.cpp
+++ b/simpleperf/environment.cpp
@@ -477,3 +477,28 @@ bool CheckSampleFrequency(uint64_t sample_freq) {
   }
   return true;
 }
+
+bool CheckKernelSymbolAddresses() {
+  const std::string kptr_restrict_file = "/proc/sys/kernel/kptr_restrict";
+  std::string s;
+  if (!android::base::ReadFileToString(kptr_restrict_file, &s)) {
+    PLOG(WARNING) << "failed to read " << kptr_restrict_file;
+    return false;
+  }
+  s = android::base::Trim(s);
+  int value;
+  if (!android::base::ParseInt(s.c_str(), &value)) {
+    LOG(ERROR) << "failed to parse " << kptr_restrict_file << ": " << s;
+    return false;
+  }
+  if (value == 0) {
+    return true;
+  }
+  if (value == 1 && IsRoot()) {
+    return true;
+  }
+  LOG(WARNING) << "Access to kernel symbol addresses is restricted. If "
+      << "possible, please do `echo 0 >/proc/sys/kernel/kptr_restrict` "
+      << "to fix this.";
+  return false;
+}
diff --git a/simpleperf/environment.h b/simpleperf/environment.h
index 7c0e279b..2f0f59c7 100644
--- a/simpleperf/environment.h
+++ b/simpleperf/environment.h
@@ -71,5 +71,6 @@ bool GetExecPath(std::string* exec_path);
 
 bool CheckPerfEventLimit();
 bool CheckSampleFrequency(uint64_t sample_freq);
+bool CheckKernelSymbolAddresses();
 
 #endif  // SIMPLE_PERF_ENVIRONMENT_H_