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From:   Jann Horn <jannh@google.com>
Date:   Thu, 4 Jun 2020 16:14:15 +0200
Message-ID: <CAG48ez0H_+EBd1wekk2oddSzLsgzincyZb_dB+s5atudB23YyA@mail.gmail.com>
Subject: Re: [PATCH 5/5] gcc-plugins/stackleak: Don't instrument
 vgettimeofday.c in arm64 VDSO
To:     Will Deacon <will@kernel.org>
Cc:     Alexander Popov <alex.popov@linux.com>,
        Kees Cook <keescook@chromium.org>,
        Emese Revfy <re.emese@gmail.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Jessica Yu <jeyu@kernel.org>,
        Sven Schnelle <svens@stackframe.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Collingbourne <pcc@google.com>,
        Naohiro Aota <naohiro.aota@wdc.com>,
        Alexander Monakov <amonakov@ispras.ru>,
        Mathias Krause <minipli@googlemail.com>,
        PaX Team <pageexec@freemail.hu>,
        Brad Spengler <spender@grsecurity.net>,
        Laura Abbott <labbott@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-kbuild@vger.kernel.org,
        "the arch/x86 maintainers" <x86@kernel.org>,
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On Thu, Jun 4, 2020 at 3:58 PM Will Deacon <will@kernel.org> wrote:
> On Thu, Jun 04, 2020 at 04:49:57PM +0300, Alexander Popov wrote:
> > Don't try instrumenting functions in arch/arm64/kernel/vdso/vgettimeofday.c.
> > Otherwise that can cause issues if the cleanup pass of stackleak gcc plugin
> > is disabled.
> >
> > Signed-off-by: Alexander Popov <alex.popov@linux.com>
> > ---
> >  arch/arm64/kernel/vdso/Makefile | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> > index 3862cad2410c..9b84cafbd2da 100644
> > --- a/arch/arm64/kernel/vdso/Makefile
> > +++ b/arch/arm64/kernel/vdso/Makefile
> > @@ -32,7 +32,8 @@ UBSAN_SANITIZE                      := n
> >  OBJECT_FILES_NON_STANDARD    := y
> >  KCOV_INSTRUMENT                      := n
> >
> > -CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables
> > +CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables \
> > +             $(DISABLE_STACKLEAK_PLUGIN)
>
> I can pick this one up via arm64, thanks. Are there any other plugins we
> should be wary of? It looks like x86 filters out $(GCC_PLUGINS_CFLAGS)
> when building the vDSO.

Maybe at some point we should replace exclusions based on
GCC_PLUGINS_CFLAGS and KASAN_SANITIZE and UBSAN_SANITIZE and
OBJECT_FILES_NON_STANDARD and so on with something more generic...
something that says "this file will not be built into the normal
kernel, it contains code that runs in realmode / userspace / some
similarly weird context, and none of our instrumentation
infrastructure is available there"...