fortify: Disable -Wstringop-overread in tests

clang recently added support for -Wstringop-overread [1], which is on by
default like -Wfortify-source. This breaks the usage of -Werror in the
fortify tests, resulting in the following false positive warnings in the
kernel build:

  warning: unsafe memcmp() usage lacked '__read_overflow2' warning in lib/test_fortify/read_overflow2-memcmp.c
  warning: unsafe memcmp() usage lacked '__read_overflow' warning in lib/test_fortify/read_overflow-memcmp.c
  warning: unsafe memchr() usage lacked '__read_overflow' warning in lib/test_fortify/read_overflow-memchr.c

Examining the fortify test logs shows a warning like the following in
each of the failed logs:

  In file included from lib/test_fortify/read_overflow2-memcmp.c:5:
  lib/test_fortify/test_fortify.h:34:2: error: 'memcmp' reading 17 bytes from a region of size 16 [-Werror,-Wstringop-overread]
     34 |         TEST;
        |         ^
  lib/test_fortify/read_overflow2-memcmp.c:3:2: note: expanded from macro 'TEST'
      3 |         memcmp(large, small, sizeof(small) + 1)
        |         ^
  1 error generated.

Disable -Wstringop-overread for the fortify tests, as it defeats the
purpose of testing the Linux specific implementation of fortify, like
-Wfortify-source.

Cc: stable@vger.kernel.org
Closes: https://github.com/ClangBuiltLinux/linux/issues/2168
Link: https://github.com/llvm/llvm-project/commit/86f2e71cb8d165b59ad31a442b2391e23826133e
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260623-fix-test_fortify-for-clang-stringop-overread-v1-1-15ee8342a953@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

diff --git a/lib/test_fortify/Makefile b/lib/test_fortify/Makefile
index 399cae880e1dc111ec017dec1deaca9731e34cfd..44cd5df41a810907bf6f42af4ac4b978376ee6c2 100644 (file)
--- a/lib/test_fortify/Makefile
+++ b/lib/test_fortify/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 ccflags-y := $(call cc-disable-warning,fortify-source)
+ccflags-y += $(call cc-disable-warning,stringop-overread)
 
 quiet_cmd_test_fortify = TEST    $@
       cmd_test_fortify = $(CONFIG_SHELL) $(src)/test_fortify.sh \