kbuild: re-implement detection of CONFIG options leaked to user-space

scripts/headers_check.pl can detect references to CONFIG options in
exported headers, but it has been disabled for more than a decade.

Reverting commit 7e3fa561 ("kbuild: drop check for CONFIG_ in
headers_check") would emit the following warnings for headers_check
on x86:

usr/include/mtd/ubi-user.h:283: leaks CONFIG_MTD_UBI_BEB_LIMIT to userspace where it is not valid
usr/include/linux/cm4000_cs.h:26: leaks CONFIG_COMPAT to userspace where it is not valid
usr/include/linux/pkt_cls.h:301: leaks CONFIG_NET_CLS_ACT to userspace where it is not valid
usr/include/linux/videodev2.h:2465: leaks CONFIG_VIDEO_ADV_DEBUG to userspace where it is not valid
usr/include/linux/bpf.h:249: leaks CONFIG_EFFICIENT_UNALIGNED_ACCESS to userspace where it is not valid
usr/include/linux/bpf.h:819: leaks CONFIG_CGROUP_NET_CLASSID to userspace where it is not valid
usr/include/linux/bpf.h:1011: leaks CONFIG_IP_ROUTE_CLASSID to userspace where it is not valid
usr/include/linux/bpf.h:1742: leaks CONFIG_BPF_KPROBE_OVERRIDE to userspace where it is not valid
usr/include/linux/bpf.h:1747: leaks CONFIG_FUNCTION_ERROR_INJECTION to userspace where it is not valid
usr/include/linux/bpf.h:1936: leaks CONFIG_XFRM to userspace where it is not valid
usr/include/linux/bpf.h:2184: leaks CONFIG_BPF_LIRC_MODE2 to userspace where it is not valid
usr/include/linux/bpf.h:2210: leaks CONFIG_BPF_LIRC_MODE2 to userspace where it is not valid
usr/include/linux/bpf.h:2227: leaks CONFIG_SOCK_CGROUP_DATA to userspace where it is not valid
usr/include/linux/bpf.h:2311: leaks CONFIG_NET to userspace where it is not valid
usr/include/linux/bpf.h:2348: leaks CONFIG_NET to userspace where it is not valid
usr/include/linux/bpf.h:2422: leaks CONFIG_BPF_LIRC_MODE2 to userspace where it is not valid
usr/include/linux/bpf.h:2528: leaks CONFIG_NET to userspace where it is not valid
usr/include/linux/pktcdvd.h:37: leaks CONFIG_CDROM_PKTCDVD_WCACHE to userspace where it is not valid
usr/include/linux/hw_breakpoint.h:27: leaks CONFIG_HAVE_MIXED_BREAKPOINTS_REGS to userspace where it is not valid
usr/include/linux/raw.h:17: leaks CONFIG_MAX_RAW_DEVS to userspace where it is not valid
usr/include/linux/elfcore.h:62: leaks CONFIG_BINFMT_ELF_FDPIC to userspace where it is not valid
usr/include/linux/eventpoll.h:82: leaks CONFIG_PM_SLEEP to userspace where it is not valid
usr/include/linux/atmdev.h:104: leaks CONFIG_COMPAT to userspace where it is not valid
usr/include/asm-generic/unistd.h:651: leaks CONFIG_MMU to userspace where it is not valid
usr/include/asm-generic/bitsperlong.h:9: leaks CONFIG_64BIT to userspace where it is not valid
usr/include/asm-generic/fcntl.h:119: leaks CONFIG_64BIT to userspace where it is not valid
usr/include/asm/auxvec.h:14: leaks CONFIG_IA32_EMULATION to userspace where it is not valid
usr/include/asm/e820.h:14: leaks CONFIG_NODES_SHIFT to userspace where it is not valid
usr/include/asm/e820.h:39: leaks CONFIG_X86_PMEM_LEGACY to userspace where it is not valid
usr/include/asm/e820.h:49: leaks CONFIG_INTEL_TXT to userspace where it is not valid
usr/include/asm/mman.h:7: leaks CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS to userspace where it is not valid

Most of these are false positives because scripts/headers_check.pl
parses comment lines.

It is also false negative. arch/x86/include/uapi/asm/auxvec.h contains
CONFIG_IA32_EMULATION and CONFIG_X86_64, but the only former is reported.

It would be possible to fix scripts/headers_check.pl, of course.
However, we already have some duplicated checks between headers_check
and CONFIG_UAPI_HEADER_TEST. At this moment of time, there are still
dozens of headers excluded from the header test (usr/include/Makefile),
but we might be able to remove headers_check eventually.

I re-implemented it in scripts/headers_install.sh by using sed because
the most of code in scripts/headers_install.sh is written in sed.

This patch works like this:

[1] Run scripts/unifdef first because we need to drop the code
    surrounded by #ifdef __KERNEL__ ... #endif

[2] Remove all C style comments. The sed code is somewhat complicated
    since we need to deal with both single and multi line comments.

    Precisely speaking, a comment block is replaced with a space just
    in case.

      CONFIG_FOO/* this is a comment */CONFIG_BAR

    should be converted into:

      CONFIG_FOO CONFIG_BAR

    instead of:

      CONFIG_FOOCONFIG_BAR

[3] Match CONFIG_... pattern. It correctly matches to all CONFIG
    options that appear in a single line.

After this commit, this would detect the following warnings, all of
which are real ones.

warning: include/uapi/linux/pktcdvd.h: leak CONFIG_CDROM_PKTCDVD_WCACHE to user-space
warning: include/uapi/linux/hw_breakpoint.h: leak CONFIG_HAVE_MIXED_BREAKPOINTS_REGS to user-space
warning: include/uapi/linux/raw.h: leak CONFIG_MAX_RAW_DEVS to user-space
warning: include/uapi/linux/elfcore.h: leak CONFIG_BINFMT_ELF_FDPIC to user-space
warning: include/uapi/linux/eventpoll.h: leak CONFIG_PM_SLEEP to user-space
warning: include/uapi/linux/atmdev.h: leak CONFIG_COMPAT to user-space
warning: include/uapi/asm-generic/fcntl.h: leak CONFIG_64BIT to user-space
warning: arch/x86/include/uapi/asm/auxvec.h: leak CONFIG_IA32_EMULATION to user-space
warning: arch/x86/include/uapi/asm/auxvec.h: leak CONFIG_X86_64 to user-space
warning: arch/x86/include/uapi/asm/mman.h: leak CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS to user-space

However, it is not nice to show them right now. I created a list of
existing leakages. They are not warned, but a new leakage will be
blocked by the 0-day bot.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>

scripts/headers_install.sh

@@ -41,5 +41,77 @@ sed -E -e '
 scripts/unifdef -U__KERNEL__ -D__EXPORTED_HEADERS__ $TMPFILE > $OUTFILE
 [ $? -gt 1 ] && exit 1
 
+# Remove /* ... */ style comments, and find CONFIG_ references in code
+configs=$(sed -e '
+:comment
+	s:/\*[^*][^*]*:/*:
+	s:/\*\*\**\([^/]\):/*\1:
+	t comment
+	s:/\*\*/: :
+	t comment
+	/\/\*/! b check
+	N
+	b comment
+:print
+	P
+	D
+:check
+	s:^\(CONFIG_[[:alnum:]_]*\):\1\n:
+	t print
+	s:^[[:alnum:]_][[:alnum:]_]*::
+	s:^[^[:alnum:]_][^[:alnum:]_]*::
+	t check
+	d
+' $OUTFILE)
+
+# The entries in the following list are not warned.
+# Please do not add a new entry. This list is only for existing ones.
+# The list will be reduced gradually, and deleted eventually. (hopefully)
+#
+# The format is <file-name>:<CONFIG-option> in each line.
+config_leak_ignores="
+arch/alpha/include/uapi/asm/setup.h:CONFIG_ALPHA_LEGACY_START_ADDRESS
+arch/arc/include/uapi/asm/page.h:CONFIG_ARC_PAGE_SIZE_16K
+arch/arc/include/uapi/asm/page.h:CONFIG_ARC_PAGE_SIZE_4K
+arch/arc/include/uapi/asm/swab.h:CONFIG_ARC_HAS_SWAPE
+arch/arm/include/uapi/asm/ptrace.h:CONFIG_CPU_ENDIAN_BE8
+arch/hexagon/include/uapi/asm/ptrace.h:CONFIG_HEXAGON_ARCH_VERSION
+arch/hexagon/include/uapi/asm/user.h:CONFIG_HEXAGON_ARCH_VERSION
+arch/ia64/include/uapi/asm/cmpxchg.h:CONFIG_IA64_DEBUG_CMPXCHG
+arch/m68k/include/uapi/asm/ptrace.h:CONFIG_COLDFIRE
+arch/nios2/include/uapi/asm/swab.h:CONFIG_NIOS2_CI_SWAB_NO
+arch/nios2/include/uapi/asm/swab.h:CONFIG_NIOS2_CI_SWAB_SUPPORT
+arch/sh/include/uapi/asm/ptrace.h:CONFIG_CPU_SH5
+arch/sh/include/uapi/asm/sigcontext.h:CONFIG_CPU_SH5
+arch/sh/include/uapi/asm/stat.h:CONFIG_CPU_SH5
+arch/x86/include/uapi/asm/auxvec.h:CONFIG_IA32_EMULATION
+arch/x86/include/uapi/asm/auxvec.h:CONFIG_X86_64
+arch/x86/include/uapi/asm/mman.h:CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+include/uapi/asm-generic/fcntl.h:CONFIG_64BIT
+include/uapi/linux/atmdev.h:CONFIG_COMPAT
+include/uapi/linux/elfcore.h:CONFIG_BINFMT_ELF_FDPIC
+include/uapi/linux/eventpoll.h:CONFIG_PM_SLEEP
+include/uapi/linux/hw_breakpoint.h:CONFIG_HAVE_MIXED_BREAKPOINTS_REGS
+include/uapi/linux/pktcdvd.h:CONFIG_CDROM_PKTCDVD_WCACHE
+include/uapi/linux/raw.h:CONFIG_MAX_RAW_DEVS
+"
+
+for c in $configs
+do
+	warn=1
+
+	for ignore in $config_leak_ignores
+	do
+		if echo "$INFILE:$c" | grep -q "$ignore$"; then
+			warn=
+			break
+		fi
+	done
+
+	if [ "$warn" = 1 ]; then
+		echo "warning: $INFILE: leak $c to user-space" >&2
+	fi
+done
+
 rm -f $TMPFILE
 trap - EXIT