From 86abf9aeb3138dcee9d2c110a911dbe8108fdd62 Mon Sep 17 00:00:00 2001
From: Alex Shlyapnikov <alekseys@google.com>
Date: Thu, 23 Mar 2017 15:57:58 +0000
Subject: [PATCH] Bypass potential libc's sysconf interceptors

Summary:
sysconf(_SC_PAGESIZE) is called very early during sanitizer init and
any instrumented code (sysconf() wrapper/interceptor will likely be
instrumented) calling back to sanitizer before init is done will
most surely crash.

2nd attempt, now with glibc version checks (D31092 was reverted).

Reviewers: eugenis

Subscribers: kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D31221

llvm-svn: 298613
---
 .../lib/sanitizer_common/sanitizer_linux.cc        | 16 ++++++++++++++
 .../Linux/sysconf_interceptor_bypass_test.cc       | 25 ++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 compiler-rt/test/sanitizer_common/TestCases/Linux/sysconf_interceptor_bypass_test.cc

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc
index 24707c7..ab65e2d 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc
@@ -77,6 +77,20 @@ extern char **environ;  // provided by crt1
 #include <sys/signal.h>
 #endif
 
+#ifndef __GLIBC_PREREQ
+#define __GLIBC_PREREQ(x, y) 0
+#endif
+
+#if SANITIZER_LINUX && __GLIBC_PREREQ(2, 16)
+# define SANITIZER_USE_GETAUXVAL 1
+#else
+# define SANITIZER_USE_GETAUXVAL 0
+#endif
+
+#if SANITIZER_USE_GETAUXVAL
+#include <sys/auxv.h>
+#endif
+
 #if SANITIZER_LINUX
 // <linux/time.h>
 struct kernel_timeval {
@@ -805,6 +819,8 @@ uptr GetPageSize() {
   return 4096;
 #elif SANITIZER_LINUX && (defined(__x86_64__) || defined(__i386__))
   return EXEC_PAGESIZE;
+#elif SANITIZER_USE_GETAUXVAL
+  return getauxval(AT_PAGESZ);
 #else
   return sysconf(_SC_PAGESIZE);  // EXEC_PAGESIZE may not be trustworthy.
 #endif
diff --git a/compiler-rt/test/sanitizer_common/TestCases/Linux/sysconf_interceptor_bypass_test.cc b/compiler-rt/test/sanitizer_common/TestCases/Linux/sysconf_interceptor_bypass_test.cc
new file mode 100644
index 0000000..eb4deac
--- /dev/null
+++ b/compiler-rt/test/sanitizer_common/TestCases/Linux/sysconf_interceptor_bypass_test.cc
@@ -0,0 +1,25 @@
+// RUN: %clangxx -O2 %s -o %t && %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+
+// getauxval() used instead of sysconf() in GetPageSize() is defined starting
+// glbc version 2.16.
+#if defined(__GLIBC_PREREQ) && __GLIBC_PREREQ(2, 16)
+extern "C" long sysconf(int name) {
+  fprintf(stderr, "sysconf wrapper called\n");
+  return 0;
+}
+#endif  // defined(__GLIBC_PREREQ) && __GLIBC_PREREQ(2, 16)
+
+int main() {
+  // All we need to check is that the sysconf() interceptor defined above was
+  // not called. Should it get called, it will crash right there, any
+  // instrumented code executed before sanitizer init is finished will crash
+  // accessing non-initialized sanitizer internals. Even if it will not crash
+  // in some configuration, it should never be called anyway.
+  fprintf(stderr, "Passed\n");
+  // CHECK-NOT: sysconf wrapper called
+  // CHECK: Passed
+  // CHECK-NOT: sysconf wrapper called
+  return 0;
+}
-- 
2.7.4