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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 30sm630465pjz.24.2020.08.18.12.23.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2020 12:23:40 -0700 (PDT) Date: Tue, 18 Aug 2020 12:23:39 -0700 From: Kees Cook To: Nick Desaulniers Cc: Masahiro Yamada , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Michal Marek , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Tony Luck , Dmitry Vyukov , Michael Ellerman , Joe Perches , Joel Fernandes , Daniel Axtens , Arvind Sankar , Andy Shevchenko , Alexandru Ardelean , Yury Norov , x86@kernel.org, "H . Peter Anvin" , Ard Biesheuvel , "Paul E . McKenney" , Daniel Kiper , Bruce Ashfield , Marco Elver , Vamshi K Sthambamkadi , Andi Kleen , Linus Torvalds , =?iso-8859-1?Q?D=E1vid_Bolvansk=FD?= , Eli Friedman , stable@vger.kernel.org, Sami Tolvanen Subject: Re: [PATCH 1/4] Makefile: add -fno-builtin-stpcpy Message-ID: <202008181223.4412CAA5@keescook> References: <20200817220212.338670-1-ndesaulniers@google.com> <20200817220212.338670-2-ndesaulniers@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200817220212.338670-2-ndesaulniers@google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > Suggested-by: Dávid Bolvanský > Suggested-by: Kees Cook > Signed-off-by: Nick Desaulniers Reviewed-by: Kees Cook -- Kees Cook