linux-kernel - [PATCH v6 12/20] modpost: check static EXPORT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20230521160426.1881124-13-masahiroy@kernel.org>
Date:   Mon, 22 May 2023 01:04:17 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: [PATCH v6 12/20] modpost: check static EXPORT_SYMBOL* by modpost again

Commit 31cb50b5590f ("kbuild: check static EXPORT_SYMBOL* by script
instead of modpost") moved the static EXPORT_SYMBOL* check from the
mostpost to a shell script because I thought it must be checked per
compilation unit to avoid false negatives.

I came up with an idea to do this in modpost, against combined ELF
files. The relocation entries in ELF will find the correct exported
symbol even if there exist symbols with the same name in different
compilation units.

Again, the same sample code.

  Makefile:

    obj-y += foo1.o foo2.o

  foo1.c:

    #include <linux/export.h>
    static void foo(void) {}
    EXPORT_SYMBOL(foo);

  foo2.c:

    void foo(void) {}

Then, modpost can catch it correctly.

    MODPOST Module.symvers
  ERROR: modpost: vmlinux: local symbol 'foo' was exported

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

Changes in v6:
  - Make the symbol name in the warning more precise

 scripts/Makefile.build     |  4 ---
 scripts/check-local-export | 70 --------------------------------------
 scripts/mod/modpost.c      |  7 ++++
 3 files changed, 7 insertions(+), 74 deletions(-)
 delete mode 100755 scripts/check-local-export

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 6bf026a304e4..bd4123795299 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -220,8 +220,6 @@ cmd_gen_ksymdeps = \
 	$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
 endif
 
-cmd_check_local_export = $(srctree)/scripts/check-local-export $@
-
 ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
 cmd_warn_shared_object = $(if $(word 2, $(modname-multi)),$(warning $(kbuild-file): $*.o is added to multiple modules: $(modname-multi)))
 endif
@@ -229,7 +227,6 @@ endif
 define rule_cc_o_c
 	$(call cmd_and_fixdep,cc_o_c)
 	$(call cmd,gen_ksymdeps)
-	$(call cmd,check_local_export)
 	$(call cmd,checksrc)
 	$(call cmd,checkdoc)
 	$(call cmd,gen_objtooldep)
@@ -241,7 +238,6 @@ endef
 define rule_as_o_S
 	$(call cmd_and_fixdep,as_o_S)
 	$(call cmd,gen_ksymdeps)
-	$(call cmd,check_local_export)
 	$(call cmd,gen_objtooldep)
 	$(call cmd,gen_symversions_S)
 	$(call cmd,warn_shared_object)
diff --git a/scripts/check-local-export b/scripts/check-local-export
deleted file mode 100755
index 969a313b9299..000000000000
--- a/scripts/check-local-export
+++ /dev/null
@@ -1,70 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0-only
-#
-# Copyright (C) 2022 Masahiro Yamada <masahiroy@...nel.org>
-# Copyright (C) 2022 Owen Rafferty <owen@...nrafferty.com>
-#
-# Exit with error if a local exported symbol is found.
-# EXPORT_SYMBOL should be used for global symbols.
-
-set -e
-pid=$$
-
-# If there is no symbol in the object, ${NM} (both GNU nm and llvm-nm) shows
-# 'no symbols' diagnostic (but exits with 0). It is harmless and hidden by
-# '2>/dev/null'. However, it suppresses real error messages as well. Add a
-# hand-crafted error message here.
-#
-# TODO:
-# Use --quiet instead of 2>/dev/null when we upgrade the minimum version of
-# binutils to 2.37, llvm to 13.0.0.
-# Then, the following line will be simpler:
-#   { ${NM} --quiet ${1} || kill 0; } |
-
-{ ${NM} ${1} 2>/dev/null || { echo "${0}: ${NM} failed" >&2; kill $pid; } } |
-${AWK} -v "file=${1}" '
-BEGIN {
-	i = 0
-}
-
-# Skip the line if the number of fields is less than 3.
-#
-# case 1)
-#   For undefined symbols, the first field (value) is empty.
-#   The outout looks like this:
-#     "                 U _printk"
-#   It is unneeded to record undefined symbols.
-#
-# case 2)
-#   For Clang LTO, llvm-nm outputs a line with type t but empty name:
-#     "---------------- t"
-!length($3) {
-	next
-}
-
-# save (name, type) in the associative array
-{ symbol_types[$3]=$2 }
-
-# append the exported symbol to the array
-($3 ~ /^__export_symbol_(gpl)?_.*/) {
-	export_symbols[i] = $3
-	sub(/^__export_symbol_(gpl)?_/, "", export_symbols[i])
-	i++
-}
-
-END {
-	exit_code = 0
-	for (j = 0; j < i; ++j) {
-		name = export_symbols[j]
-		# nm(3) says "If lowercase, the symbol is usually local"
-		if (symbol_types[name] ~ /[a-z]/) {
-			printf "%s: error: local symbol %s was exported\n",
-				file, name | "cat 1>&2"
-			exit_code = 1
-		}
-	}
-
-	exit exit_code
-}'
-
-exit $?
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 8b94090d0743..dd1d066f1214 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1235,6 +1235,13 @@ static void check_export_symbol(struct module *mod, struct elf_info *elf,
 		return;
 	}
 
+	if (ELF_ST_BIND(sym->st_info) != STB_GLOBAL &&
+	    ELF_ST_BIND(sym->st_info) != STB_WEAK) {
+		error("%s: local symbol '%s' was exported\n", mod->name,
+		      label_name + strlen(prefix));
+		return;
+	}
+
 	if (strcmp(label_name + strlen(prefix), name)) {
 		error("%s: .export_symbol section references '%s', but it does not seem to be an export symbol\n",
 		      mod->name, name);
-- 
2.39.2