commit c1f3e770eec26d6f96dd6d2ea30555ba7c09a244 upstream.

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 [1]
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>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

commit 4e9903b0861c9df3464b82db4a7025863bac1897 upstream.

There are some issues in the test_fortify Makefile code.

Problem 1: cc-disable-warning invokes compiler dozens of times

To see how many times the cc-disable-warning is evaluated, change
this code:

  $(call cc-disable-warning,fortify-source)

to:

  $(call cc-disable-warning,$(shell touch /tmp/fortify-$$$$)fortify-source)

Then, build the kernel with CONFIG_FORTIFY_SOURCE=y. You will see a
large number of '/tmp/fortify-<PID>' files created:

  $ ls -1 /tmp/fortify-* | wc
       80      80    1600

This means the compiler was invoked 80 times just for checking the
-Wno-fortify-source flag support.

$(call cc-disable-warning,fortify-source) should be added to a simple
variable instead of a recursive variable.

Problem 2: do not recompile string.o when the test code is updated

The test cases are independent of the kernel. However, when the test
code is updated, $(obj)/string.o is rebuilt and vmlinux is relinked
due to this dependency:

  $(obj)/string.o: $(obj)/$(TEST_FORTIFY_LOG)

always-y is suitable for building the log files.

Problem 3: redundant code

  clean-files += $(addsuffix .o, $(TEST_FORTIFY_LOGS))

... is unneeded because the top Makefile globally cleans *.o files.

This commit fixes these issues and makes the code readable.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20240727150302.1823750-2-masahiroy@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
[nathan: Fixed conflicts]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>