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authorJohn Högberg <[email protected]>2018-11-20 10:46:25 +0100
committerJohn Högberg <[email protected]>2018-11-20 15:54:40 +0100
commitbbd72b63ce63eab7006ebb571d750771e30061b6 (patch)
treeab56e15eda0e25b5dc9608481a08a1bbe2eca145
parentda06fd040775fffee17409ebbd6fa797e34d6f99 (diff)
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Add a ./configure flag for spectre mitigation
Note that the ERTS_NO_RETPOLINE macro introduced by this commit is completely inert unless spectre-mitigation is set to 'incomplete.' This includes when mitigation has been manually enabled through CFLAGS, so it should be impossible for it to unintentionally disable mitigation.
-rw-r--r--erts/configure.in50
1 files changed, 50 insertions, 0 deletions
diff --git a/erts/configure.in b/erts/configure.in
index ad9a66126f..4d1464d744 100644
--- a/erts/configure.in
+++ b/erts/configure.in
@@ -416,6 +416,56 @@ if test X"$with_ets_write_concurrency_locks" != X""; then
[Define to override the default number of write_concurrency locks])
fi
+AC_ARG_WITH(spectre-mitigation,
+ AS_HELP_STRING([--with-spectre-mitigation={yes|incomplete}],
+ [enable spectre mitigation, either fully or with mitigations
+ disabled in a handful places like the interpreter])
+ AS_HELP_STRING([--without-spectre-mitigation],
+ [build without spectre mitigation]),
+ [],[with_spectre_mitigation=no])
+
+case "$with_spectre_mitigation" in
+ no) ;;
+ yes) ;;
+ incomplete) ;;
+ *) AC_MSG_ERROR([Invalid spectre mitigation setting]) ;;
+esac
+
+i_noretpoline_attr=""
+
+if test X"$with_spectre_mitigation" != X"no"; then
+ CFLAGS="$CFLAGS -mindirect-branch=thunk"
+
+ AC_MSG_CHECKING([for spectre mitigation])
+ AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM([],[return 0;])],
+ [AC_MSG_RESULT([yes])],
+ [AC_MSG_ERROR([no])])
+
+ if test X"$with_spectre_mitigation" = X"incomplete"; then
+ # gcc and clang support this attribute if they're recent enough. Note
+ # that we must compile with -Werror to check for actual support as they
+ # warn rather than error out on unsupported attributes.
+
+ i_noretpoline_attr='__attribute__((__indirect_branch__("keep")))'
+ i_preserve_cflags="$CFLAGS"
+ CFLAGS="$CFLAGS -Werror"
+
+ AC_MSG_CHECKING([whether spectre mitigation can be disabled on a per-function basis])
+ AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM([$i_noretpoline_attr],[return 0;])],
+ [AC_MSG_RESULT([yes])],
+ [AC_MSG_ERROR([no])])
+
+ CFLAGS="$i_preserve_cflags"
+ fi
+fi
+
+AC_DEFINE_UNQUOTED(ERTS_NO_RETPOLINE, $i_noretpoline_attr,
+ [Per-function attribute for disabling retpoline. This is
+ *only* defined when --with-spectre-mitigation=incomplete
+ and has no effects otherwise])
+
dnl ----------------------------------------------------------------------
dnl Checks for programs.
dnl ----------------------------------------------------------------------