[PATCH 3/8] Enable vDSO on interposed malloc linked statically

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

For statically linked binaries, _dl_non_dynamic_init (csu/init-first.c:74)
calls malloc before the vDSO is properly initialized (it will fully usable
only after VDSO_SETUP call).  The bug is triggered for the cases where an
interposed malloc calls clock_gettime or any other implementation that may
call a vDSO symbol.

It is because PTR_DEMANDLE at {INLINE,INTERNAL}_VSYSCALL is called with
uninitialized __vdso_* pointer value, which should be done by PTR_MANGLE
(zero-initialized value in this case is invalid).  The patch fixes by adding
an extra hook before _dl_non_dynamic_init which setup the initial __vdso_*
pointer symbol to an mangled NULL value.

For NULL mangled values {INLINE,INTERNAL}_VSYSCALL issues the syscall
directly in fallback code path.  Once the __vdso_* is setup the vsyscall
branches to vDSO.

Checked on x86_64-linux-gnu.

	[BZ #24967]
	* sysdeps/unix/sysv/linux/init-first.c (libc_vdso_mangled_symbol):
	New symbol.
	(__libc_vdso_platform_setup): Add an option to call it to initialize
	the hooks to null values.
	(VDSO_PRE_SETUP): Define.
	* csu/init-first.c (_init): Add a pre-hook to initialize the vDSO
	internal pointer.
	* malloc/tst-interpose-aux.c (allocation_header): Add ts member.
	(malloc_internal): Call clock_gettime.
---
 csu/init-first.c                     |  8 ++++++
 malloc/tst-interpose-aux.c           |  5 ++++
 sysdeps/unix/sysv/linux/init-first.c | 37 +++++++++++++++++++---------
 3 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/csu/init-first.c b/csu/init-first.c
index 10762b61f5..d984419554 100644
--- a/csu/init-first.c
+++ b/csu/init-first.c
@@ -69,6 +69,14 @@ _init (int argc, char **argv, char **envp)
   __environ = envp;
 
 #ifndef SHARED
+  /* Initialize the vDSO internal pointers to mangled zero value.  It makes
+     the {INTERNAL,INLINE}_VSYSCALL macro to fallback to direct syscall
+     and allows call the symbol that might the vDSO on _dl_non_dynamic_init
+     (for instance clock_gettime on an interposed malloc).  */
+# ifdef VDSO_PRE_SETUP
+  VDSO_PRE_SETUP ();
+# endif
+
   /* First the initialization which normally would be done by the
      dynamic linker.  */
   _dl_non_dynamic_init ();
diff --git a/malloc/tst-interpose-aux.c b/malloc/tst-interpose-aux.c
index bf86224401..de62d436bc 100644
--- a/malloc/tst-interpose-aux.c
+++ b/malloc/tst-interpose-aux.c
@@ -28,6 +28,7 @@
 #include <sys/mman.h>
 #include <sys/uio.h>
 #include <unistd.h>
+#include <time.h>
 
 #if INTERPOSE_THREADS
 #include <pthread.h>
@@ -96,6 +97,7 @@ struct __attribute__ ((aligned (__alignof__ (max_align_t)))) allocation_header
 {
   size_t allocation_index;
   size_t allocation_size;
+  struct timespec ts;
 };
 
 /* Array of known allocations, to track invalid frees.  */
@@ -166,6 +168,9 @@ malloc_internal (size_t size)
       .allocation_index = index,
       .allocation_size = allocation_size
     };
+  /* Check if calling a symbol which may use the vDSO does not fail.
+     The CLOCK_REALTIME should be supported on all systems.  */
+  clock_gettime (CLOCK_REALTIME, &allocations[index]->ts);
   return allocations[index] + 1;
 }
 
diff --git a/sysdeps/unix/sysv/linux/init-first.c b/sysdeps/unix/sysv/linux/init-first.c
index d90ca820be..a23e5d9f6e 100644
--- a/sysdeps/unix/sysv/linux/init-first.c
+++ b/sysdeps/unix/sysv/linux/init-first.c
@@ -44,37 +44,52 @@ long int (*VDSO_SYMBOL(getcpu)) (unsigned *, unsigned *, void *)
 time_t (*VDSO_SYMBOL(time)) (time_t *) attribute_hidden;
 #endif
 
+static inline void *
+__libc_vdso_mangled_symbol (const char *symbol)
+{
+  void *vdsop = NULL;
+  if (symbol != NULL)
+    vdsop = get_vdso_mangle_symbol (symbol);
+  else
+    PTR_MANGLE (vdsop);
+  return vdsop;
+}
+
 static inline void
-__libc_vdso_platform_setup (void)
+__libc_vdso_platform_setup (bool initial)
 {
 #ifdef HAVE_CLOCK_GETTIME_VSYSCALL
-  VDSO_SYMBOL(clock_gettime)
-    = get_vdso_mangle_symbol (HAVE_CLOCK_GETTIME_VSYSCALL);
+  VDSO_SYMBOL(clock_gettime) =
+    __libc_vdso_mangled_symbol (initial ? NULL : HAVE_CLOCK_GETTIME_VSYSCALL);
 #endif
 
 #ifdef HAVE_CLOCK_GETRES_VSYSCALL
-  VDSO_SYMBOL(clock_getres)
-    = get_vdso_mangle_symbol (HAVE_CLOCK_GETRES_VSYSCALL);
+  VDSO_SYMBOL(clock_getres) =
+    __libc_vdso_mangled_symbol (initial ? NULL : HAVE_CLOCK_GETRES_VSYSCALL);
 #endif
 
 #ifdef HAVE_GETTIMEOFDAY_VSYSCALL
-  VDSO_SYMBOL(gettimeofday)
-    = get_vdso_mangle_symbol (HAVE_GETTIMEOFDAY_VSYSCALL);
+  VDSO_SYMBOL(gettimeofday) =
+    __libc_vdso_mangled_symbol (initial ? NULL : HAVE_GETTIMEOFDAY_VSYSCALL);
 #endif
 
 #ifdef HAVE_GETCPU_VSYSCALL
-  VDSO_SYMBOL(getcpu) = get_vdso_mangle_symbol (HAVE_GETCPU_VSYSCALL);
+  VDSO_SYMBOL(getcpu) =
+    __libc_vdso_mangled_symbol (initial ? NULL : HAVE_GETCPU_VSYSCALL);
 #endif
 
 #ifdef HAVE_TIME_VSYSCALL
-  VDSO_SYMBOL(time) = get_vdso_mangle_symbol (HAVE_TIME_VSYSCALL);
+  VDSO_SYMBOL(time) =
+    __libc_vdso_mangled_symbol (initial ? NULL : HAVE_TIME_VSYSCALL);
 #endif
 
 #ifdef VDSO_SETUP_ARCH
-  VDSO_SETUP_ARCH ();
+  if (!initial)
+    VDSO_SETUP_ARCH ();
 #endif
 }
 
-#define VDSO_SETUP __libc_vdso_platform_setup
+#define VDSO_PRE_SETUP() ({ __libc_vdso_platform_setup (true); })
+#define VDSO_SETUP()     ({ __libc_vdso_platform_setup (false); })
 
 #include <csu/init-first.c>
-- 
2.17.1