fortify: Explicitly disable Clang support

stable inclusion
from stable-5.10.81
commit eaafc590053b314d4907017044ba2e739893c17c
bugzilla: 185832 https://gitee.com/openeuler/kernel/issues/I4L9CF

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eaafc590053b314d4907017044ba2e739893c17c

--------------------------------

commit a52f8a59 upstream.

Clang has never correctly compiled the FORTIFY_SOURCE defenses due to
a couple bugs:

	Eliding inlines with matching __builtin_* names
	https://bugs.llvm.org/show_bug.cgi?id=50322

	Incorrect __builtin_constant_p() of some globals
	https://bugs.llvm.org/show_bug.cgi?id=41459

In the process of making improvements to the FORTIFY_SOURCE defenses, the
first (silent) bug (coincidentally) becomes worked around, but exposes
the latter which breaks the build. As such, Clang must not be used with
CONFIG_FORTIFY_SOURCE until at least latter bug is fixed (in Clang 13),
and the fortify routines have been rearranged.

Update the Kconfig to reflect the reality of the current situation.
Signed-off-by: NKees Cook <keescook@chromium.org>
Acked-by: NNick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/lkml/CAKwvOd=A+ueGV2ihdy5GtgR2fQbcXjjAtVxv3=cPjffpebZB7A@mail.gmail.com
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

security/Kconfig

@@ -191,6 +191,9 @@ config HARDENED_USERCOPY_PAGESPAN
 config FORTIFY_SOURCE
 	bool "Harden common str/mem functions against buffer overflows"
 	depends on ARCH_HAS_FORTIFY_SOURCE
+	# https://bugs.llvm.org/show_bug.cgi?id=50322
+	# https://bugs.llvm.org/show_bug.cgi?id=41459
+	depends on !CC_IS_CLANG
 	help
 	  Detect overflows of buffers in common string and memory functions
 	  where the compiler can determine and validate the buffer sizes.