Re: [PATCH] compiler-gcc.h: Define __SANITIZE_ADDRESS__ under hwaddress sanitizer

From: Kees Cook <keescook@chromium.org>
To: Marco Elver <elver@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Masahiro Yamada <masahiroy@kernel.org>,
	llvm@lists.linux.dev, Ard Biesheuvel <ardb@kernel.org>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
	Andrey Konovalov <andreyknvl@gmail.com>,
	kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH] compiler-gcc.h: Define __SANITIZE_ADDRESS__ under hwaddress sanitizer
Date: Thu, 21 Oct 2021 01:43:09 -0700	[thread overview]
Message-ID: <202110210141.18C98C4@keescook> (raw)
In-Reply-To: <CANpmjNMPaLpw_FoMzmShLSEBNq_Cn6t86tO_FiYLR2eD001=4Q@mail.gmail.com>

On Thu, Oct 21, 2021 at 08:00:00AM +0200, Marco Elver wrote:
> On Wed, 20 Oct 2021 at 22:00, Kees Cook <keescook@chromium.org> wrote:
> > When Clang is using the hwaddress sanitizer, it sets __SANITIZE_ADDRESS__
> > explicitly:
> >
> >  #if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
> >  /* Emulate GCC's __SANITIZE_ADDRESS__ flag */
> >  #define __SANITIZE_ADDRESS__
> >  #endif
> 
> Hmm, the comment is a little inaccurate if hwaddress sanitizer is on,
> but I certainly wouldn't want compiler-clang.h to start emulating gcc
> here and start defining __SANITIZE_HWADDRESS__ if the places where we
> check it are the same as __SANITIZE_ADDRESS__. So this patch is the
> right approach.

Yeah, I agree. I think that was Arnd's thinking as well.

> 
> > Once hwaddress sanitizer was added to GCC, however, a separate define
> > was created, __SANITIZE_HWADDRESS__. The kernel is expecting to find
> > __SANITIZE_ADDRESS__ in either case, though, and the existing string
> > macros break on supported architectures:
> >
> >  #if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
> >           !defined(__SANITIZE_ADDRESS__)
> >
> > where as other architectures (like arm32) have no idea about hwaddress
> > sanitizer and just check for __SANITIZE_ADDRESS__:
> >
> >  #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
> 
> arm32 doesn't support KASAN_SW_TAGS, so I think the bit about arm32 is
> irrelevant.

Right -- I had just picked an example.

> Only arm64 can, and the reason that arm64 doesn't check against
> "defined(CONFIG_KASAN)" is because we also have KASAN_HW_TAGS (no
> compiler instrumentation).
> 
> > This would lead to compiler foritfy self-test warnings when building
> > with CONFIG_KASAN_SW_TAGS=y:
> >
> > warning: unsafe memmove() usage lacked '__read_overflow2' symbol in lib/test_fortify/read_overflow2-memmove.c
> > warning: unsafe memcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-memcpy.c
> > ...
> >
> > Sort this out by also defining __SANITIZE_ADDRESS__ in GCC under the
> > hwaddress sanitizer.
> >
> > Suggested-by: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nathan Chancellor <nathan@kernel.org>
> > Cc: Nick Desaulniers <ndesaulniers@google.com>
> > Cc: Miguel Ojeda <ojeda@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Marco Elver <elver@google.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Arvind Sankar <nivedita@alum.mit.edu>
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Cc: llvm@lists.linux.dev
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> Other than that,
> 
>   Reviewed-by: Marco Elver <elver@google.com>

Thanks! (Oh, BTW, it seems "b4" won't include your Reviewed-by: tag if
it is indented like this.)

-Kees

-- 
Kees Cook