Bypass potential libc's sysconf interceptors

[alekseyshl]

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).

[kcc]

lib/sanitizer_common/sanitizer_linux.cc

84

I would put the two ifdefs in sync

#if SANITIZER_LINUX && __GLIBC_PREREQ(2, 16)

define SANITIZER_USE_GETAUXVAL 1

#else

define SANITIZER_USE_GETAUXVAL 0

#endif

then use SANITIZER_USE_GETAUXVAL

[alekseyshl]

• Sync two ifdefs

[kcc]

LGTM

[eugenis]

LGTM

lib/sanitizer_common/sanitizer_linux.cc

 }
 extern char **environ;  // provided by crt1
 #endif  // SANITIZER_FREEBSD
 
 #if !SANITIZER_ANDROID
 #include <sys/signal.h>
 #endif
 
+#ifndef __GLIBC_PREREQ
+#define __GLIBC_PREREQ(x, y) 0
+#endif
+
+#if SANITIZER_LINUX && __GLIBC_PREREQ(2, 16)
+#include <sys/auxv.h>
+#endif
+
 #if SANITIZER_LINUX
 // <linux/time.h>
 struct kernel_timeval {
   long tv_sec;
   long tv_usec;
 };
 
 // <linux/futex.h> is broken on some linux distributions.

 }
 
 uptr GetPageSize() {
 // Android post-M sysconf(_SC_PAGESIZE) crashes if called from .preinit_array.
 #if SANITIZER_ANDROID
   return 4096;
 #elif SANITIZER_LINUX && (defined(__x86_64__) || defined(__i386__))
   return EXEC_PAGESIZE;
+#elif SANITIZER_LINUX && __GLIBC_PREREQ(2, 16)
+  return getauxval(AT_PAGESZ);
 #else
   return sysconf(_SC_PAGESIZE);  // EXEC_PAGESIZE may not be trustworthy.
 #endif
 }
 
 uptr ReadBinaryName(/*out*/char *buf, uptr buf_len) {
 #if SANITIZER_FREEBSD
   const int Mib[] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };

test/sanitizer_common/TestCases/Linux/sysconf_interceptor_bypass_test.cc

+// 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;
+}