Revert "Revert "Merge pull request #28029 from cstrahan/hardening-fix""

This reverts commit 6c064e6b1f, reapplying
PR #28029 which was supposed to have gone to staging all along.

pkgs/build-support/cc-wrapper/add-flags.sh

@@ -30,10 +30,10 @@ fi
 # We need to mangle names for hygiene, but also take parameters/overrides
 # from the environment.
 for var in "${var_templates_list[@]}"; do
-    mangleVarList "$var" "${role_infixes[@]}"
+    mangleVarList "$var" ${role_infixes[@]+"${role_infixes[@]}"}
 done
 for var in "${var_templates_bool[@]}"; do
-    mangleVarBool "$var" "${role_infixes[@]}"
+    mangleVarBool "$var" ${role_infixes[@]+"${role_infixes[@]}"}
 done
 
 # `-B@out@/bin' forces cc to use ld-wrapper.sh when calling ld.

pkgs/build-support/cc-wrapper/add-hardening.sh

@@ -1,67 +1,72 @@
-hardeningFlags=(fortify stackprotector pic strictoverflow format relro bindnow)
-# Intentionally word-split in case 'hardeningEnable' is defined in
-# Nix. Also, our bootstrap tools version of bash is old enough that
-# undefined arrays trip `set -u`.
-if [[ -v hardeningEnable[@] ]]; then
-  hardeningFlags+=(${hardeningEnable[@]})
-fi
-hardeningCFlags=()
+declare -a hardeningCFlags=()
 
-declare -A hardeningDisableMap
+declare -A hardeningEnableMap=()
 
-# Intentionally word-split in case 'hardeningDisable' is defined in Nix.
-for flag in ${hardeningDisable[@]:-IGNORED_KEY} @hardening_unsupported_flags@
-do
-  hardeningDisableMap[$flag]=1
+# Intentionally word-split in case 'NIX_HARDENING_ENABLE' is defined in Nix. The
+# array expansion also prevents undefined variables from causing trouble with
+# `set -u`.
+for flag in ${NIX_@infixSalt@_HARDENING_ENABLE-}; do
+  hardeningEnableMap["$flag"]=1
+done
+
+# Remove unsupported flags.
+for flag in @hardening_unsupported_flags@; do
+  unset -v hardeningEnableMap["$flag"]
 done
 
 if (( "${NIX_DEBUG:-0}" >= 1 )); then
+  declare -a allHardeningFlags=(fortify stackprotector pie pic strictoverflow format)
+  declare -A hardeningDisableMap=()
+
+  # Determine which flags were effectively disabled so we can report below.
+  for flag in "${allHardeningFlags[@]}"; do
+    if [[ -z "${hardeningEnableMap[$flag]-}" ]]; then
+      hardeningDisableMap["$flag"]=1
+    fi
+  done
+
   printf 'HARDENING: disabled flags:' >&2
   (( "${#hardeningDisableMap[@]}" )) && printf ' %q' "${!hardeningDisableMap[@]}" >&2
   echo >&2
-fi
 
-if [[ -z "${hardeningDisableMap[all]:-}" ]]; then
-  if (( "${NIX_DEBUG:-0}" >= 1 )); then
+  if (( "${#hardeningEnableMap[@]}" )); then
     echo 'HARDENING: Is active (not completely disabled with "all" flag)' >&2;
   fi
-  for flag in "${hardeningFlags[@]}"
-  do
-    if [[ -z "${hardeningDisableMap[$flag]:-}" ]]; then
-      case $flag in
-        fortify)
-          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling fortify >&2; fi
-          hardeningCFlags+=('-O2' '-D_FORTIFY_SOURCE=2')
-          ;;
-        stackprotector)
-          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling stackprotector >&2; fi
-          hardeningCFlags+=('-fstack-protector-strong' '--param' 'ssp-buffer-size=4')
-          ;;
-        pie)
-          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling CFlags -fPIE >&2; fi
-          hardeningCFlags+=('-fPIE')
-          if [[ ! ("$*" =~ " -shared " || "$*" =~ " -static ") ]]; then
-            if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling LDFlags -pie >&2; fi
-            hardeningCFlags+=('-pie')
-          fi
-          ;;
-        pic)
-          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling pic >&2; fi
-          hardeningCFlags+=('-fPIC')
-          ;;
-        strictoverflow)
-          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling strictoverflow >&2; fi
-          hardeningCFlags+=('-fno-strict-overflow')
-          ;;
-        format)
-          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling format >&2; fi
-          hardeningCFlags+=('-Wformat' '-Wformat-security' '-Werror=format-security')
-          ;;
-        *)
-          # Ignore unsupported. Checked in Nix that at least *some*
-          # tool supports each flag.
-          ;;
-      esac
-    fi
-  done
 fi
+
+for flag in "${!hardeningEnableMap[@]}"; do
+  case $flag in
+    fortify)
+      if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling fortify >&2; fi
+      hardeningCFlags+=('-O2' '-D_FORTIFY_SOURCE=2')
+      ;;
+    stackprotector)
+      if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling stackprotector >&2; fi
+      hardeningCFlags+=('-fstack-protector-strong' '--param' 'ssp-buffer-size=4')
+      ;;
+    pie)
+      if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling CFlags -fPIE >&2; fi
+      hardeningCFlags+=('-fPIE')
+      if [[ ! ("$*" =~ " -shared " || "$*" =~ " -static ") ]]; then
+        if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling LDFlags -pie >&2; fi
+        hardeningCFlags+=('-pie')
+      fi
+      ;;
+    pic)
+      if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling pic >&2; fi
+      hardeningCFlags+=('-fPIC')
+      ;;
+    strictoverflow)
+       if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling strictoverflow >&2; fi
+      hardeningCFlags+=('-fno-strict-overflow')
+      ;;
+    format)
+      if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling format >&2; fi
+      hardeningCFlags+=('-Wformat' '-Wformat-security' '-Werror=format-security')
+      ;;
+    *)
+      # Ignore unsupported. Checked in Nix that at least *some*
+      # tool supports each flag.
+      ;;
+  esac
+done

pkgs/build-support/cc-wrapper/cc-wrapper.sh

@@ -134,8 +134,8 @@ fi
 source @out@/nix-support/add-hardening.sh
 
 # Add the flags for the C compiler proper.
-extraAfter=($NIX_@infixSalt@_CFLAGS_COMPILE "${hardeningCFlags[@]}")
-extraBefore=()
+extraAfter=($NIX_@infixSalt@_CFLAGS_COMPILE)
+extraBefore=(${hardeningCFlags[@]+"${hardeningCFlags[@]}"})
 
 if [ "$dontLink" != 1 ]; then
 

pkgs/build-support/cc-wrapper/setup-hook.sh

@@ -147,6 +147,10 @@ export ${role_pre}CXX=@named_cxx@
 export CC${role_post}=@named_cc@
 export CXX${role_post}=@named_cxx@
 
+# If unset, assume the default hardening flags.
+: ${NIX_HARDENING_ENABLE="fortify stackprotector pic strictoverflow format relro bindnow"}
+export NIX_HARDENING_ENABLE
+
 # No local scope in sourced file
 unset -v role_pre role_post
 set +u