kbuild: do not include include/config/auto.conf from shell scripts

Richard Weinberger pointed out the risk of sourcing the kernel config
from shell scripts [1], and proposed some patches [2], [3]. It is a good
point, but it took a long time because I was wondering how to fix this.

This commit goes with simple grep approach because there are only a few
scripts including the kernel configuration.

scripts/link_vmlinux.sh has references to a bunch of CONFIG options,
all of which are boolean. I added is_enabled() helper as
scripts/package/{mkdebian,builddeb} do.

scripts/gen_autoksyms.sh uses 'eval', stating "to expand the whitelist
path". I removed it since it is the issue we are trying to fix.

I was a bit worried about the cost of invoking the grep command over
again. I extracted the grep parts from it, and measured the cost. It
was approximately 0.03 sec, which I hope is acceptable.

[test code]

  $ cat test-grep.sh
  #!/bin/sh

  is_enabled() {
          grep -q "^$1=y" include/config/auto.conf
  }

  is_enabled CONFIG_LTO_CLANG
  is_enabled CONFIG_LTO_CLANG
  is_enabled CONFIG_STACK_VALIDATION
  is_enabled CONFIG_UNWINDER_ORC
  is_enabled CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
  is_enabled CONFIG_VMLINUX_VALIDATION
  is_enabled CONFIG_FRAME_POINTER
  is_enabled CONFIG_GCOV_KERNEL
  is_enabled CONFIG_LTO_CLANG
  is_enabled CONFIG_RETPOLINE
  is_enabled CONFIG_X86_SMAP
  is_enabled CONFIG_LTO_CLANG
  is_enabled CONFIG_VMLINUX_MAP
  is_enabled CONFIG_KALLSYMS_ALL
  is_enabled CONFIG_KALLSYMS_ABSOLUTE_PERCPU
  is_enabled CONFIG_KALLSYMS_BASE_RELATIVE
  is_enabled CONFIG_DEBUG_INFO_BTF
  is_enabled CONFIG_KALLSYMS
  is_enabled CONFIG_DEBUG_INFO_BTF
  is_enabled CONFIG_BPF
  is_enabled CONFIG_BUILDTIME_TABLE_SORT
  is_enabled CONFIG_KALLSYMS

  $ time ./test-grep.sh
  real    0m0.036s
  user    0m0.027s
  sys     m0.009s

[1]: https://lore.kernel.org/all/1919455.eZKeABUfgV@blindfold/
[2]: https://lore.kernel.org/all/20180219092245.26404-1-richard@nod.at/
[3]: https://lore.kernel.org/all/20210920213957.1064-2-richard@nod.at/Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>

scripts/gen_autoksyms.sh

@@ -16,20 +16,15 @@ case "$KBUILD_VERBOSE" in
 	;;
 esac
 
-# We need access to CONFIG_ symbols
-. include/config/auto.conf
-
 needed_symbols=
 
 # Special case for modversions (see modpost.c)
-if [ -n "$CONFIG_MODVERSIONS" ]; then
+if grep -q "^CONFIG_MODVERSIONS=y$" include/config/auto.conf; then
 	needed_symbols="$needed_symbols module_layout"
 fi
 
-ksym_wl=
-if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
-	# Use 'eval' to expand the whitelist path and check if it is relative
-	eval ksym_wl="$CONFIG_UNUSED_KSYMS_WHITELIST"
+ksym_wl=$(sed -n 's/^CONFIG_UNUSED_KSYMS_WHITELIST="\(.*\)"$/\1/p' include/config/auto.conf)
+if [ -n "$ksym_wl" ]; then
 	[ "${ksym_wl}" != "${ksym_wl#/}" ] || ksym_wl="$abs_srctree/$ksym_wl"
 	if [ ! -f "$ksym_wl" ] || [ ! -r "$ksym_wl" ]; then
 		echo "ERROR: '$ksym_wl' whitelist file not found" >&2

scripts/link-vmlinux.sh

@@ -34,6 +34,10 @@ LD="$1"
 KBUILD_LDFLAGS="$2"
 LDFLAGS_vmlinux="$3"
 
+is_enabled() {
+	grep -q "^$1=y" include/config/auto.conf
+}
+
 # Nice output in kbuild format
 # Will be supressed by "make -s"
 info()
@@ -80,11 +84,11 @@ modpost_link()
 		${KBUILD_VMLINUX_LIBS}				\
 		--end-group"
 
-	if [ -n "${CONFIG_LTO_CLANG}" ]; then
+	if is_enabled CONFIG_LTO_CLANG; then
 		gen_initcalls
 		lds="-T .tmp_initcalls.lds"
 
-		if [ -n "${CONFIG_MODVERSIONS}" ]; then
+		if is_enabled CONFIG_MODVERSIONS; then
 			gen_symversions
 			lds="${lds} -T .tmp_symversions.lds"
 		fi
@@ -104,21 +108,21 @@ objtool_link()
 	local objtoolcmd;
 	local objtoolopt;
 
-	if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then
+	if is_enabled CONFIG_LTO_CLANG && is_enabled CONFIG_STACK_VALIDATION; then
 		# Don't perform vmlinux validation unless explicitly requested,
 		# but run objtool on vmlinux.o now that we have an object file.
-		if [ -n "${CONFIG_UNWINDER_ORC}" ]; then
+		if is_enabled CONFIG_UNWINDER_ORC; then
 			objtoolcmd="orc generate"
 		fi
 
 		objtoolopt="${objtoolopt} --duplicate"
 
-		if [ -n "${CONFIG_FTRACE_MCOUNT_USE_OBJTOOL}" ]; then
+		if is_enabled CONFIG_FTRACE_MCOUNT_USE_OBJTOOL; then
 			objtoolopt="${objtoolopt} --mcount"
 		fi
 	fi
 
-	if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then
+	if is_enabled CONFIG_VMLINUX_VALIDATION; then
 		objtoolopt="${objtoolopt} --noinstr"
 	fi
 
@@ -127,16 +131,16 @@ objtool_link()
 			objtoolcmd="check"
 		fi
 		objtoolopt="${objtoolopt} --vmlinux"
-		if [ -z "${CONFIG_FRAME_POINTER}" ]; then
+		if ! is_enabled CONFIG_FRAME_POINTER; then
 			objtoolopt="${objtoolopt} --no-fp"
 		fi
-		if [ -n "${CONFIG_GCOV_KERNEL}" ] || [ -n "${CONFIG_LTO_CLANG}" ]; then
+		if is_enabled CONFIG_GCOV_KERNEL || is_enabled CONFIG_LTO_CLANG; then
 			objtoolopt="${objtoolopt} --no-unreachable"
 		fi
-		if [ -n "${CONFIG_RETPOLINE}" ]; then
+		if is_enabled CONFIG_RETPOLINE; then
 			objtoolopt="${objtoolopt} --retpoline"
 		fi
-		if [ -n "${CONFIG_X86_SMAP}" ]; then
+		if is_enabled CONFIG_X86_SMAP; then
 			objtoolopt="${objtoolopt} --uaccess"
 		fi
 		info OBJTOOL ${1}
@@ -161,7 +165,7 @@ vmlinux_link()
 	# skip output file argument
 	shift
 
-	if [ -n "${CONFIG_LTO_CLANG}" ]; then
+	if is_enabled CONFIG_LTO_CLANG; then
 		# Use vmlinux.o instead of performing the slow LTO link again.
 		objs=vmlinux.o
 		libs=
@@ -189,7 +193,7 @@ vmlinux_link()
 		ldflags="${ldflags} ${wl}--strip-debug"
 	fi
 
-	if [ -n "${CONFIG_VMLINUX_MAP}" ]; then
+	if is_enabled CONFIG_VMLINUX_MAP; then
 		ldflags="${ldflags} ${wl}-Map=${output}.map"
 	fi
 
@@ -239,15 +243,15 @@ kallsyms()
 {
 	local kallsymopt;
 
-	if [ -n "${CONFIG_KALLSYMS_ALL}" ]; then
+	if is_enabled CONFIG_KALLSYMS_ALL; then
 		kallsymopt="${kallsymopt} --all-symbols"
 	fi
 
-	if [ -n "${CONFIG_KALLSYMS_ABSOLUTE_PERCPU}" ]; then
+	if is_enabled CONFIG_KALLSYMS_ABSOLUTE_PERCPU; then
 		kallsymopt="${kallsymopt} --absolute-percpu"
 	fi
 
-	if [ -n "${CONFIG_KALLSYMS_BASE_RELATIVE}" ]; then
+	if is_enabled CONFIG_KALLSYMS_BASE_RELATIVE; then
 		kallsymopt="${kallsymopt} --base-relative"
 	fi
 
@@ -312,9 +316,6 @@ if [ "$1" = "clean" ]; then
 	exit 0
 fi
 
-# We need access to CONFIG_ symbols
-. include/config/auto.conf
-
 # Update version
 info GEN .version
 if [ -r .version ]; then
@@ -343,7 +344,7 @@ tr '\0' '\n' < modules.builtin.modinfo | sed -n 's/^[[:alnum:]:_]*\.file=//p' |
 	tr ' ' '\n' | uniq | sed -e 's:^:kernel/:' -e 's/$/.ko/' > modules.builtin
 
 btf_vmlinux_bin_o=""
-if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
+if is_enabled CONFIG_DEBUG_INFO_BTF; then
 	btf_vmlinux_bin_o=.btf.vmlinux.bin.o
 	if ! gen_btf .tmp_vmlinux.btf $btf_vmlinux_bin_o ; then
 		echo >&2 "Failed to generate BTF for vmlinux"
@@ -355,7 +356,7 @@ fi
 kallsymso=""
 kallsymso_prev=""
 kallsyms_vmlinux=""
-if [ -n "${CONFIG_KALLSYMS}" ]; then
+if is_enabled CONFIG_KALLSYMS; then
 
 	# kallsyms support
 	# Generate section listing all symbols and add it into vmlinux
@@ -395,12 +396,12 @@ fi
 vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
 
 # fill in BTF IDs
-if [ -n "${CONFIG_DEBUG_INFO_BTF}" -a -n "${CONFIG_BPF}" ]; then
+if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
 	info BTFIDS vmlinux
 	${RESOLVE_BTFIDS} vmlinux
 fi
 
-if [ -n "${CONFIG_BUILDTIME_TABLE_SORT}" ]; then
+if is_enabled CONFIG_BUILDTIME_TABLE_SORT; then
 	info SORTTAB vmlinux
 	if ! sorttable vmlinux; then
 		echo >&2 Failed to sort kernel tables
@@ -412,7 +413,7 @@ info SYSMAP System.map
 mksysmap vmlinux System.map
 
 # step a (see comment above)
-if [ -n "${CONFIG_KALLSYMS}" ]; then
+if is_enabled CONFIG_KALLSYMS; then
 	mksysmap ${kallsyms_vmlinux} .tmp_System.map
 
 	if ! cmp -s System.map .tmp_System.map; then

scripts/setlocalversion

@@ -111,9 +111,7 @@ if $scm_only; then
 	exit
 fi
 
-if test -e include/config/auto.conf; then
-	. include/config/auto.conf
-else
+if ! test -e include/config/auto.conf; then
 	echo "Error: kernelrelease not valid - run 'make prepare' to update it" >&2
 	exit 1
 fi
@@ -125,10 +123,11 @@ if test ! "$srctree" -ef .; then
 fi
 
 # CONFIG_LOCALVERSION and LOCALVERSION (if set)
-res="${res}${CONFIG_LOCALVERSION}${LOCALVERSION}"
+config_localversion=$(sed -n 's/^CONFIG_LOCALVERSION="\(.*\)"$/\1/p' include/config/auto.conf)
+res="${res}${config_localversion}${LOCALVERSION}"
 
 # scm version string if not at a tagged commit
-if test "$CONFIG_LOCALVERSION_AUTO" = "y"; then
+if grep -q "^CONFIG_LOCALVERSION_AUTO=y$" include/config/auto.conf; then
 	# full scm version string
 	res="$res$(scm_version)"
 elif [ "${LOCALVERSION+set}" != "set" ]; then