linux-kernel - Re: [PATCH 06/14] Fix CFLAGS for UBSAN

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Date:   Wed, 16 Sep 2020 07:40:27 +0000
From:   George Popescu <georgepope@...gle.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>, maz@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu, LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        james.morse@....com, julien.thierry.kdev@...il.com,
        suzuki.poulose@....com,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        David Brazdil <dbrazdil@...gle.com>, broonie@...nel.org,
        Fangrui Song <maskray@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 06/14] Fix CFLAGS for UBSAN_BOUNDS on Clang

On Tue, Sep 15, 2020 at 07:32:28PM +0200, Marco Elver wrote:
> On Tue, 15 Sep 2020 at 14:01, George Popescu <georgepope@...gle.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@...gle.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@...gle.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> 

I don't have CONFIG_UBSAN_TRAP=y. My .config is:
CONFIG_ARCH_HAS_UBSAN_SANITIZE_ALL=y
CONFIG_UBSAN=y
# CONFIG_UBSAN_TRAP is not set
CONFIG_UBSAN_KCOV_BROKEN=y
CONFIG_UBSAN_MISC=y
CONFIG_UBSAN_SANITIZE_ALL=y
# CONFIG_UBSAN_ALIGNMENT is not set
CONFIG_TEST_UBSAN=m

Thanks,
George