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[34.77.222.49]) by smtp.gmail.com with ESMTPSA id w15sm27651716wro.46.2020.09.15.03.25.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2020 03:25:00 -0700 (PDT) Date: Tue, 15 Sep 2020 10:24:58 +0000 From: George Popescu To: Kees Cook Cc: maz@kernel.org, catalin.marinas@arm.com, will@kernel.org, masahiroy@kernel.org, michal.lkml@markovi.net, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, natechancellor@gmail.com, ndesaulniers@google.com, dbrazdil@google.com, broonie@kernel.org, maskray@google.com, ascull@google.com, akpm@linux-foundation.org, dvyukov@google.com, elver@google.com, tglx@linutronix.de, arnd@arndb.de Subject: Re: [PATCH 06/14] Fix CFLAGS for UBSAN_BOUNDS on Clang Message-ID: <20200915102458.GA1650630@google.com> References: <20200914172750.852684-1-georgepope@google.com> <20200914172750.852684-7-georgepope@google.com> <202009141509.CDDC8C8@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202009141509.CDDC8C8@keescook> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 14, 2020 at 03:13:14PM -0700, Kees Cook wrote: > On Mon, Sep 14, 2020 at 05:27:42PM +0000, George-Aurelian Popescu wrote: > > From: George Popescu > > > > When the kernel is compiled with Clang, UBSAN_BOUNDS inserts a brk after > > the handler call, preventing it from printing any information processed > > inside the buffer. > > For Clang -fsanitize=bounds expands to -fsanitize=array-bounds and > > -fsanitize=local-bounds, and the latter adds a brk after the handler > > call > > That sounds like a compiler bug? Actually in clang 12 documentation is written that -fsanitize=bounds expands to that. GCC doesn't have those two options, only the -fsanitize=bounds which looks similar to -fsanitize=array-bounds from clang. So I don't see it as a compiler bug, just a misuse of flags. > > Signed-off-by: George Popescu > > --- > > scripts/Makefile.ubsan | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan > > index 27348029b2b8..3d15ac346c97 100644 > > --- a/scripts/Makefile.ubsan > > +++ b/scripts/Makefile.ubsan > > @@ -4,7 +4,14 @@ ifdef CONFIG_UBSAN_ALIGNMENT > > endif > > > > ifdef CONFIG_UBSAN_BOUNDS > > - CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds) > > + # For Clang -fsanitize=bounds translates to -fsanitize=array-bounds and > > + # -fsanitize=local-bounds; the latter adds a brk right after the > > + # handler is called. > > + ifdef CONFIG_CC_IS_CLANG > > + CFLAGS_UBSAN += $(call cc-option, -fsanitize=array-bounds) > > This would mean losing the local-bounds coverage? Isn't that for locally > defined arrays on the stack? This would mean losing the local-bounds coverage. I tried to test it without local-bounds and with a locally defined array on the stack and it works fine (the handler is called and the error reported). For me it feels like --array-bounds and --local-bounds are triggered for the same type of undefined_behaviours but they are handling them different. > > + else > > + CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds) > > + endif > > endif > > > > ifdef CONFIG_UBSAN_MISC > > -- > > 2.28.0.618.gf4bc123cb7-goog > > > > -- Thanks, George