[PATCH 5.15 11/20] fortify: Explicitly disable Clang support

From: Greg Kroah-Hartman
Date: Fri Nov 19 2021 - 12:40:05 EST

From: Kees Cook <keescook@xxxxxxxxxxxx>

commit a52f8a59aef46b59753e583bf4b28fccb069ce64 upstream.

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

Eliding inlines with matching __builtin_* names

Incorrect __builtin_constant_p() of some globals

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: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/CAKwvOd=A+ueGV2ihdy5GtgR2fQbcXjjAtVxv3=cPjffpebZB7A@xxxxxxxxxxxxxx
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
security/Kconfig | 3 +++
1 file changed, 3 insertions(+)

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