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From:   Marco Elver <elver@google.com>
Date:   Tue, 15 Sep 2020 19:32:28 +0200
Message-ID: <CANpmjNPpq7LfTHYesz2wTVw6Pqv0FQ2gc-vmSB6Mdov+XWPZiw@mail.gmail.com>
Subject: Re: [PATCH 06/14] Fix CFLAGS for UBSAN_BOUNDS on Clang
To:     George Popescu <georgepope@google.com>
Cc:     Kees Cook <keescook@chromium.org>, maz@kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        kvmarm@lists.cs.columbia.edu, LKML <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        james.morse@arm.com, julien.thierry.kdev@gmail.com,
        suzuki.poulose@arm.com,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        David Brazdil <dbrazdil@google.com>, broonie@kernel.org,
        Fangrui Song <maskray@google.com>,
        Andrew Scull <ascull@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Arnd Bergmann <arnd@arndb.de>
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On Tue, 15 Sep 2020 at 14:01, George Popescu <georgepope@google.com> wrote:
>
> On Tue, Sep 15, 2020 at 01:18:11PM +0200, Marco Elver wrote:
> > On Tue, 15 Sep 2020 at 12:25, George Popescu <georgepope@google.com> wrote:
> > > 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 <georgepope@google.com>
> > > > >
> > > > > 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
> > > >
> > > 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.
> >
> > Does -fno-sanitize-trap=bounds help?>
>
> I tried replacing it with:
>       ifdef CONFIG_CC_IS_CLANG
>             CFLAGS_UBSAN += $(call cc-option, -fno-sanitize-trap=bounds)
>             CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
>       else
>             CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
>       endif
>
> The code traps.

What's your config? Do you have CONFIG_UBSAN_TRAP=y? If so, you have 2
options: honor UBSAN_TRAP and crash the kernel, or have a
'CFLAGS_REMOVE_... = -fsanitize-undefined-trap-on-error' for the files
where you can't deal with traps.

Thanks,
-- Marco