LLVM implemented a recent "libcall optimization" that lowers calls to `sprintf(dest, "%s", str)` where the return value is used to `stpcpy(dest, str) - dest`. This generally avoids the machinery involved in parsing format strings. This optimization was introduced into clang-12. Because the kernel does not provide an implementation of stpcpy, we observe linkage failures for almost all targets when building with ToT clang. The interface is unsafe as it does not perform any bounds checking. Disable this "libcall optimization" via `-fno-builtin-stpcpy`. Cc: stable@xxxxxxxxxxxxxxx # 4.4 Link: https://bugs.llvm.org/show_bug.cgi?id=47162 Link: https://github.com/ClangBuiltLinux/linux/issues/1126 Link: https://reviews.llvm.org/D85963 Reported-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> Suggested-by: Dávid Bolvanský <david.bolvansky@xxxxxxxxx> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> --- Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/Makefile b/Makefile index 9cac6fde3479..e523dc8d30e0 100644 --- a/Makefile +++ b/Makefile @@ -578,6 +578,7 @@ ifneq ($(LLVM_IAS),1) CLANG_FLAGS += -no-integrated-as endif CLANG_FLAGS += -Werror=unknown-warning-option +CLANG_FLAGS += -fno-builtin-stpcpy KBUILD_CFLAGS += $(CLANG_FLAGS) KBUILD_AFLAGS += $(CLANG_FLAGS) export CLANG_FLAGS -- 2.28.0.297.g1956fa8f8d-goog
