From: Marco Elver <elver@google.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Borislav Petkov <bp@alien8.de>, Rong Chen <rong.a.chen@intel.com>,
kernel test robot <lkp@intel.com>,
"Li, Philip" <philip.li@intel.com>, x86-ml <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
kasan-dev <kasan-dev@googlegroups.com>,
Ilie Halip <ilie.halip@gmail.com>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e
Date: Wed, 16 Sep 2020 10:59:01 +0200 [thread overview]
Message-ID: <CANpmjNPa8FuTURfO0btWir4ax7jBy79P5x7Z5h08e-Ybea1Fnw@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdmptEpi8fiOyWUo=AiZJiX+Z+VHJOM2buLPrWsMTwLnyw@mail.gmail.com>
On Wed, 16 Sep 2020 at 00:34, Nick Desaulniers <ndesaulniers@google.com> wrote:
> On Tue, Sep 15, 2020 at 2:02 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > panic() is noreturn, so the compiler is enforcing the fact that it
> > doesn't return, by trapping if it does return.
> >
> > I seem to remember that's caused by CONFIG_UBSAN_TRAP.
>
> Indeed, if I remove CONFIG_UBSAN_TRAP from the 0day report's
> randconfig, these unreachable instruction warnings all go away.
>
> So what's the right way to fix this?
>
> CONFIG_UBSAN_TRAP enables -fsanitize-undefined-trap-on-error (not
> sure why that's wrapped in cc-option; it shouldn't be selectable via
> Kconfig if unsupported by the toolchain).
>
> Should clang not be emitting `ud2` trapping instructions for this flag
> for no-return functions?
I think this would defeat the purpose of this UBSAN feature. Certain
UBSAN checks are done fully statically, like is done by
fsanitize=unreachable, and could actually be enabled in production
kernels; trapping the kernel in these cases would be a reasonable way
to avoid further damage to the system.
(You could in theory force it to not emit a trap by using
fno-sanitize-trap=unreachable, but I think it's a bad idea.)
> or
>
> Should objtool be made aware of the config option and then not check
> traps after no-returns?
I'd vote for this. And it seems Ilie implemented this already.
> I suspect the latter, but I'm not sure how feasible it is to
> implement. Josh, Marco, do you have thoughts on the above?
Thanks,
-- Marco
next prev parent reply other threads:[~2020-09-16 8:59 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 13:42 [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e kernel test robot
2020-09-15 13:55 ` Borislav Petkov
2020-09-15 14:18 ` Rong Chen
2020-09-15 14:41 ` Borislav Petkov
2020-09-15 16:05 ` Borislav Petkov
2020-09-15 17:02 ` Josh Poimboeuf
2020-09-15 17:21 ` Borislav Petkov
2020-09-15 17:34 ` Borislav Petkov
2020-09-15 17:41 ` Nick Desaulniers
2020-09-15 18:01 ` Borislav Petkov
2020-09-15 18:04 ` Nick Desaulniers
2020-09-15 17:40 ` Nick Desaulniers
2020-09-15 18:09 ` Marco Elver
2020-09-16 8:30 ` peterz
2020-09-16 8:46 ` Marco Elver
2020-09-16 9:06 ` peterz
2020-09-16 9:33 ` Marco Elver
2020-09-16 18:22 ` Nick Desaulniers
2020-09-16 18:51 ` Marco Elver
2020-09-17 4:11 ` Fangrui Song
[not found] ` <333D40A0-4550-4309-9693-1ABA4AC75399@arm.com>
2020-09-17 11:04 ` Mark Rutland
2020-09-17 11:16 ` Daniel Kiss
2020-09-17 18:39 ` Josh Poimboeuf
2020-09-15 17:44 ` Nick Desaulniers
2020-09-15 20:12 ` Nick Desaulniers
2020-09-15 20:49 ` Borislav Petkov
2020-09-15 21:02 ` Josh Poimboeuf
2020-09-15 21:14 ` Borislav Petkov
2020-09-15 22:34 ` Nick Desaulniers
2020-09-16 7:03 ` Ilie Halip
2020-09-16 8:59 ` Marco Elver [this message]
2020-09-21 16:51 ` [tip: objtool/core] objtool: Ignore unreachable trap after call to noreturn functions tip-bot2 for Ilie Halip
2020-09-15 21:50 ` [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e Arvind Sankar
2020-09-15 21:59 ` Nick Desaulniers
2020-09-15 22:44 ` Arvind Sankar
2020-09-16 11:34 ` Borislav Petkov
2020-09-16 18:28 ` Nick Desaulniers
2020-09-16 18:48 ` Borislav Petkov
2020-09-15 21:13 ` Nick Desaulniers
2020-09-15 21:28 ` Josh Poimboeuf
2020-09-15 23:35 ` Marco Elver
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