On Mon, Aug 17, 2020 at 03:02:09PM -0700, Nick Desaulniers wrote:
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`.
Unlike commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") which cited failures with `-fno-builtin-*` flags being retained in LLVM LTO, that bug seems to have been fixed by https://reviews.llvm.org/D71193, so the above sha can now be reverted in favor of `-fno-builtin-bcmp`.
Cc: stable@vger.kernel.org # 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@google.com Suggested-by: Dávid Bolvanský david.bolvansky@gmail.com Suggested-by: Kees Cook keescook@chromium.org Signed-off-by: Nick Desaulniers ndesaulniers@google.com
Reviewed-by: Kees Cook keescook@chromium.org