linux-kernel - Re: [PATCH] compiler-gcc.h: Define __SANITIZE_ADDRESS_

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Date:   Thu, 21 Oct 2021 01:43:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Masahiro Yamada <masahiroy@...nel.org>, llvm@...ts.linux.dev,
        Ard Biesheuvel <ardb@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] compiler-gcc.h: Define __SANITIZE_ADDRESS__ under
 hwaddress sanitizer

On Thu, Oct 21, 2021 at 08:00:00AM +0200, Marco Elver wrote:
> On Wed, 20 Oct 2021 at 22:00, Kees Cook <keescook@...omium.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@...db.de>
> > Cc: Nathan Chancellor <nathan@...nel.org>
> > Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> > Cc: Miguel Ojeda <ojeda@...nel.org>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Marco Elver <elver@...gle.com>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Arvind Sankar <nivedita@...m.mit.edu>
> > Cc: Masahiro Yamada <masahiroy@...nel.org>
> > Cc: llvm@...ts.linux.dev
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> Other than that,
> 
>   Reviewed-by: Marco Elver <elver@...gle.com>

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

-Kees

-- 
Kees Cook