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From: Jann Horn <jannh@google.com>
To: Sami Tolvanen <samitolvanen@google.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"the arch/x86 maintainers" <x86@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Will Deacon <will@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-kbuild@vger.kernel.org,
	kernel list <linux-kernel@vger.kernel.org>,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps
Date: Thu, 15 Oct 2020 01:23:41 +0200
Message-ID: <CAG48ez2baAvKDA0wfYLKy-KnM_1CdOwjU873VJGDM=CErjsv_A@mail.gmail.com> (raw)
In-Reply-To: <20201013003203.4168817-23-samitolvanen@google.com>

+objtool folks

On Tue, Oct 13, 2020 at 2:35 AM Sami Tolvanen <samitolvanen@google.com> wrote:
> Running objtool --vmlinux --duplicate on vmlinux.o produces a few
> warnings about indirect jumps with retpoline:
>
>   vmlinux.o: warning: objtool: wakeup_long64()+0x61: indirect jump
>   found in RETPOLINE build
>   ...
>
> This change adds ANNOTATE_RETPOLINE_SAFE annotations to the jumps
> in assembly code to stop the warnings.

In other words, this patch deals with the fact that
OBJECT_FILES_NON_STANDARD stops being effective for object files that
are linked into the main kernel when LTO is on, right?
All the files you're touching here are supposed to be excluded from
objtool warnings at the moment:

$ grep OBJECT_FILES_NON_STANDARD arch/x86/kernel/acpi/Makefile
OBJECT_FILES_NON_STANDARD_wakeup_$(BITS).o := y
$ grep OBJECT_FILES_NON_STANDARD arch/x86/platform/pvh/Makefile
OBJECT_FILES_NON_STANDARD_head.o := y
$ grep OBJECT_FILES_NON_STANDARD arch/x86/power/Makefile
OBJECT_FILES_NON_STANDARD_hibernate_asm_$(BITS).o := y

It would probably be good to keep LTO and non-LTO builds in sync about
which files are subjected to objtool checks. So either you should be
removing the OBJECT_FILES_NON_STANDARD annotations for anything that
is linked into the main kernel (which would be a nice cleanup, if that
is possible), or alternatively ensure that code from these files is
excluded from objtool checks even with LTO (that'd probably be messy
and a bad idea?).

Grepping for other files marked as OBJECT_FILES_NON_STANDARD that
might be included in the main kernel on x86, I also see stuff like:

    5 arch/x86/crypto/Makefile                            5
OBJECT_FILES_NON_STANDARD := y
   10 arch/x86/kernel/Makefile                           39
OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o          := y
   12 arch/x86/kvm/Makefile                               7
OBJECT_FILES_NON_STANDARD_vmenter.o := y

for which I think the same thing applies.

  parent reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-13  0:31 [PATCH v6 00/25] Add support for Clang LTO Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 01/25] kbuild: preprocess module linker script Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 02/25] objtool: Add a pass for generating __mcount_loc Sami Tolvanen
2020-10-14 16:50   ` Ingo Molnar
2020-10-14 18:21     ` Peter Zijlstra
2020-10-15 20:10       ` Josh Poimboeuf
2020-10-13  0:31 ` [PATCH v6 03/25] objtool: Don't autodetect vmlinux.o Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 04/25] tracing: move function tracer options to Kconfig Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 05/25] tracing: add support for objtool mcount Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 06/25] x86, build: use " Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 07/25] treewide: remove DISABLE_LTO Sami Tolvanen
2020-10-14 22:43   ` Kees Cook
2020-10-17  1:46     ` Masahiro Yamada
2020-10-13  0:31 ` [PATCH v6 08/25] kbuild: add support for Clang LTO Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 09/25] kbuild: lto: fix module versioning Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 10/25] objtool: Split noinstr validation from --vmlinux Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 11/25] kbuild: lto: postpone objtool Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 12/25] kbuild: lto: limit inlining Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 13/25] kbuild: lto: merge module sections Sami Tolvanen
2020-10-14 22:49   ` Kees Cook
2020-10-20 16:42     ` Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 14/25] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-10-14 22:50   ` Kees Cook
2020-10-13  0:31 ` [PATCH v6 15/25] init: lto: ensure initcall ordering Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 16/25] init: lto: fix PREL32 relocations Sami Tolvanen
2020-10-14 22:53   ` Kees Cook
2020-10-15  0:12   ` Jann Horn
2020-10-13  0:31 ` [PATCH v6 17/25] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-10-14 22:58   ` Kees Cook
2020-10-13  0:31 ` [PATCH v6 18/25] modpost: lto: strip .lto from module names Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 19/25] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 20/25] efi/libstub: disable LTO Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 21/25] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-10-13  0:32 ` [PATCH v6 22/25] x86/asm: annotate indirect jumps Sami Tolvanen
2020-10-14 22:46   ` Kees Cook
2020-10-14 23:23   ` Jann Horn [this message]
2020-10-15 10:22     ` Peter Zijlstra
2020-10-15 20:39       ` Josh Poimboeuf
2020-10-20 16:45         ` Sami Tolvanen
2020-10-20 18:52           ` Josh Poimboeuf
2020-10-20 19:24             ` Sami Tolvanen
2020-10-21  8:56               ` Peter Zijlstra
2020-10-21  9:08                 ` Peter Zijlstra
2020-10-21  9:32                 ` Peter Zijlstra
2020-10-21 21:27                   ` Josh Poimboeuf
2020-10-22  7:25                     ` Peter Zijlstra
2020-10-23 17:48                       ` Sami Tolvanen
2020-10-23 18:04                         ` Nick Desaulniers
2020-10-21 15:01                 ` Sami Tolvanen
2020-10-22  0:22                 ` Sami Tolvanen
2020-10-23 17:36                   ` Sami Tolvanen
2020-11-09 23:11                     ` Sami Tolvanen
2020-11-10  2:29                       ` Josh Poimboeuf
2020-11-10  3:18                         ` Nick Desaulniers
2020-11-10  4:48                         ` Sami Tolvanen
2020-11-10 16:11                           ` Josh Poimboeuf
2020-11-10 17:46                         ` Josh Poimboeuf
2020-11-10 18:59                           ` Sami Tolvanen
2020-11-13 19:54                             ` Josh Poimboeuf
2020-11-13 20:24                               ` Sami Tolvanen
2020-11-13 20:52                                 ` Josh Poimboeuf
2020-11-13 22:34                                 ` Josh Poimboeuf
2020-11-13 22:54                                   ` Sami Tolvanen
2020-11-13 22:56                                     ` Josh Poimboeuf
2020-11-13 23:31                                   ` Sami Tolvanen
2020-11-14  0:49                                     ` Josh Poimboeuf
2020-10-21  9:51             ` Peter Zijlstra
2020-10-21 18:30               ` Josh Poimboeuf
2020-10-13  0:32 ` [PATCH v6 23/25] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-10-13  0:32 ` [PATCH v6 24/25] x86, cpu: disable LTO for cpu.c Sami Tolvanen
2020-10-13  0:32 ` [PATCH v6 25/25] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen

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