Add backwards compatible implementation of explicit_bzero

Fuzzbawls · furszy · commit ed6adcd7ba68 · 2020-08-02T23:08:05.000-03:00
This makes `explicit_bzero` compatible with our minimum required glibc
version.
diff --git a/src/Makefile.am b/src/Makefile.am
@@ -538,6 +538,11 @@ libsapling_a_SOURCES = \
   sapling/crypter_sapling.cpp \
   sapling/saplingscriptpubkeyman.cpp
 
+if GLIBC_BACK_COMPAT
+libsapling_a_SOURCES += compat/glibc_compat.cpp
+AM_LDFLAGS += $(COMPAT_LDFLAGS)
+endif
+
 # cli: shared between pivx-cli and pivx-qt
 libbitcoin_cli_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_cli_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
diff --git a/src/compat/glibc_compat.cpp b/src/compat/glibc_compat.cpp
@@ -9,6 +9,9 @@
 
 #include <cstddef>
 #include <cstdint>
+#include <cstring>
+#include <pthread.h>
+#include <stdlib.h>
 
 #if defined(HAVE_SYS_SELECT_H)
 #include <sys/select.h>
@@ -75,3 +78,31 @@ extern "C" float __wrap_log2f(float x)
 {
     return log2f_old(x);
 }
+
+/* glibc-internal users use __explicit_bzero_chk, and explicit_bzero
+redirects to that.  */
+#undef explicit_bzero
+/* Set LEN bytes of S to 0.  The compiler will not delete a call to
+this function, even if S is dead after the call.  */
+void explicit_bzero (void *s, size_t len)
+{
+    memset (s, '\0', len);
+    /* Compiler barrier.  */
+    asm volatile ("" ::: "memory");
+}
+
+// Redefine explicit_bzero_chk
+void __explicit_bzero_chk (void *dst, size_t len, size_t dstlen)
+{
+    /* Inline __memset_chk to avoid a PLT reference to __memset_chk.  */
+    if (__glibc_unlikely (dstlen < len))
+        __chk_fail ();
+    memset (dst, '\0', len);
+    /* Compiler barrier.  */
+    asm volatile ("" ::: "memory");
+}
+/* libc-internal references use the hidden
+__explicit_bzero_chk_internal symbol.  This is necessary if
+__explicit_bzero_chk is implemented as an IFUNC because some
+targets do not support hidden references to IFUNC symbols.  */
+#define strong_alias (__explicit_bzero_chk, __explicit_bzero_chk_internal)
