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From: Nick Desaulniers <ndesaulniers@google.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: X86 ML <x86@kernel.org>, Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	linux-hardening@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 01/15] objtool: Find a destination for jumps beyond the section end
Date: Tue, 20 Apr 2021 15:58:35 -0700	[thread overview]
Message-ID: <CAKwvOdkOu4RSw9fwr_qdh7VLHjGD4nLjMZMZxzvpJUqjsWFBww@mail.gmail.com> (raw)
In-Reply-To: <20210420225550.szbmrpwv6awd7tp5@treble>

On Tue, Apr 20, 2021 at 3:57 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Tue, Apr 20, 2021 at 01:25:43PM -0700, Sami Tolvanen wrote:
> > On Tue, Apr 20, 2021 at 11:14 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > >
> > > On Fri, Apr 16, 2021 at 01:38:30PM -0700, Sami Tolvanen wrote:
> > > > With -ffunction-sections, Clang can generate a jump beyond the end of
> > > > a section when the section ends in an unreachable instruction.
> > >
> > > Why?  Can you show an example?
> >
> > Here's the warning I'm seeing when building allyesconfig + CFI:
> >
> > vmlinux.o: warning: objtool:
> > rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c()+0x149:
> > can't find jump dest instruction at
> > .text.rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c+0x7dc
> >
> > $ objdump -d -r -j
> > .text.rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c
> > vmlinux.o
> > 0000000000000000 <rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c>:
> >   ...
> >  149:   0f 85 8d 06 00 00       jne    7dc <.compoundliteral.4>
> >   ...
> >  7d7:   e8 00 00 00 00          callq  7dc <.compoundliteral.4>
> >                         7d8: R_X86_64_PLT32     __stack_chk_fail-0x4
>
> Instead of silencing the warning by faking the jump destination, I'd
> rather improve the warning to something like
>
>   "warning: rockchip_spi_transfer_one() falls through to the next function"
>
> which is what we normally do in this type of situation.
>
> It may be caused by UB, or a compiler bug, but either way we should
> figure out the root cause.

We probably want to creduce or cvise this.  IIRC we still have
outstanding issues with switch statements with user-annotated
unreachable branches not getting eliminated.
-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2021-04-20 22:58 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 20:38 [PATCH 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 01/15] objtool: Find a destination for jumps beyond the section end Sami Tolvanen
2021-04-20 18:14   ` Josh Poimboeuf
2021-04-20 20:25     ` Sami Tolvanen
2021-04-20 22:55       ` Josh Poimboeuf
2021-04-20 22:58         ` Nick Desaulniers [this message]
2021-04-16 20:38 ` [PATCH 02/15] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-04-20 19:47   ` Josh Poimboeuf
2021-04-20 20:45     ` Sami Tolvanen
2021-04-16 20:38 ` [PATCH 03/15] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-04-16 20:38 ` [PATCH 04/15] static_call: Use global functions for the self-test Sami Tolvanen
2021-04-16 21:37   ` Thomas Gleixner
2021-04-17  0:16     ` Thomas Gleixner
2021-04-16 20:38 ` [PATCH 05/15] x86: Implement function_nocfi Sami Tolvanen
2021-04-16 21:18   ` Borislav Petkov
2021-04-16 21:49     ` Sami Tolvanen
2021-04-16 22:02       ` Borislav Petkov
2021-04-16 22:06         ` Andy Lutomirski
2021-04-16 22:14           ` Borislav Petkov
2021-04-16 22:20             ` Andy Lutomirski
2021-04-16 22:37               ` Kees Cook
2021-04-16 23:02                 ` Thomas Gleixner
2021-04-17 10:16                   ` Thomas Gleixner
2021-04-19 15:13                     ` Sami Tolvanen
2021-04-16 22:28           ` Kees Cook
2021-04-16 22:52             ` Andy Lutomirski
2021-04-16 22:58               ` Kees Cook
2021-04-16 23:40               ` Kees Cook
2021-04-17 23:19                 ` Andy Lutomirski
2021-04-17 23:53                   ` Thomas Gleixner
2021-04-18  0:11                     ` Andy Lutomirski
2021-04-18 16:17                       ` Thomas Gleixner
2021-04-18 22:57                         ` Andy Lutomirski
2021-04-19 15:20                           ` Sami Tolvanen
2021-04-19 15:26                       ` David Laight
2021-04-19 17:46                         ` Andy Lutomirski
2021-04-17 14:20             ` David Laight
2021-04-17 15:48               ` Andy Lutomirski
2021-04-19  8:40             ` Rasmus Villemoes
2021-04-19 16:45               ` Joao Moreira
2021-04-19 21:52               ` David Laight
2021-04-16 22:16         ` Kees Cook
2021-04-16 22:13       ` Thomas Gleixner
2021-04-16 20:38 ` [PATCH 06/15] x86: Avoid CFI jump tables in IDT and entry points Sami Tolvanen
2021-04-16 22:26   ` Thomas Gleixner
2021-04-16 23:56     ` Kees Cook
2021-04-17  0:02       ` Thomas Gleixner
2021-04-16 20:38 ` [PATCH 07/15] x86/ftrace: Use function_nocfi in MCOUNT_ADDR Sami Tolvanen
2021-04-16 20:38 ` [PATCH 08/15] x86/extable: Do not mark exception callback as CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 09/15] x86/alternatives: Use C int3 selftest but disable KASAN Sami Tolvanen
2021-04-17 11:37   ` Peter Zijlstra
2021-04-19 15:26     ` Sami Tolvanen
2021-04-20  7:19       ` Peter Zijlstra
2021-04-16 20:38 ` [PATCH 10/15] x86/purgatory: Disable CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 11/15] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-04-16 20:38 ` [PATCH 12/15] x86, module: " Sami Tolvanen
2021-04-16 20:38 ` [PATCH 13/15] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-04-16 20:38 ` [PATCH 14/15] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-04-16 20:38 ` [PATCH 15/15] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen

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