File 0324-Add-a-.-configure-flag-for-spectre-mitigation.patch of Package erlang
From bbd72b63ce63eab7006ebb571d750771e30061b6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20H=C3=B6gberg?= <john@erlang.org>
Date: Tue, 20 Nov 2018 10:46:25 +0100
Subject: [PATCH 1/2] 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.
---
erts/configure.in | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
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 ----------------------------------------------------------------------
--
2.16.4
