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From: "Fāng-ruì Sòng" <maskray@google.com>
To: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>, Borislav Petkov <bp@alien8.de>,
	linux-hardening@vger.kernel.org, x86@kernel.org,
	Jesse Brandeburg <jesse.brandeburg@intel.com>,
	Kristen Carlson Accardi <kristen@linux.intel.com>,
	Kees Cook <keescook@chromium.org>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Ard Biesheuvel <ardb@kernel.org>, Tony Luck <tony.luck@intel.com>,
	Bruce Schlobohm <bruce.schlobohm@intel.com>,
	Jessica Yu <jeyu@kernel.org>, kernel test robot <lkp@intel.com>,
	Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Marios Pomonis <pomonis@google.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Nicolas Pitre <nico@fluxnic.net>,
	linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
	linux-arch@vger.kernel.org, live-patching@vger.kernel.org,
	llvm@lists.linux.dev
Subject: Re: [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search
Date: Tue, 4 Jan 2022 19:24:56 -0800	[thread overview]
Message-ID: <20220105032456.hs3od326sdl4zjv4@google.com> (raw)
In-Reply-To: <20220103160615.7904-1-alexandr.lobakin@intel.com>

On 2022-01-03, Alexander Lobakin wrote:
>From: Miroslav Benes <mbenes@suse.cz>
>Date: Mon, 3 Jan 2022 14:55:42 +0100 (CET)
>
>> On Thu, 30 Dec 2021, Fāng-ruì Sòng wrote:
>>
>> > On Thu, Dec 30, 2021 at 3:11 AM Borislav Petkov <bp@alien8.de> wrote:
>> > >
>> > > On Thu, Dec 23, 2021 at 01:21:56AM +0100, Alexander Lobakin wrote:
>> > > > [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search
>>
>> ...
>>
>> > Apologies since I haven't read the patch series.
>> >
>> > The option does not exist in ld.lld and I am a bit concerning about
>> > its semantics: https://maskray.me/blog/2020-11-15-explain-gnu-linker-options#z-unique-symbol
>> >
>> > I thought that someone forwarded my comments (originally posted months
>> > on a feature request ago) here but seems not.
>> > (I am a ld.lld maintainer.)
>>
>> Do you mean
>> https://lore.kernel.org/all/20210123225928.z5hkmaw6qjs2gu5g@google.com/T/#u
>> ?
>>
>> Unfortunately, it did not lead anywhere. I think that '-z unique-symbol'
>> option should work fine as long as the live patching is concerned. Maybe I
>> misunderstood but your concerns mentioned at the blog do not apply. The
>> stability is not an issue for us since we (KLP) always work with already
>> built and fixed kernel. And(at least) GCC already uses number suffices for
>> IPA clones and it has not been a problem anywhere.

The stability problem may not happen frequently but is possible if the
compiler performs some IPA with new code.

Such disturbence is probably more likely with LTO or PGO.
For Clang LTO, Makefile currently specifies -mllvm -import-instr-limit=5.
If a function close to the boundary happens to cross the boundary,
if inlined into other translation units, the stability issue may affect
many translation units.

>LLD doesn't have such an option, so FG-KASLR + livepatching builds
>wouldn't be available for LLVM with the current approach (or we'd
>still need a stub that prints "FG-KASLR is not compatible with
>sympos != 0").
>Unfortunately, I discovered this a bit late, just after sending this
>revision.
>
>OTOH, there's no easy alternative. <file + function> pair looks
>appealing, but is it even possible for now to implement in the
>kernel without much refactoring?

<file + symbol> pair looks good to me and will solve the stability problem.

  reply	other threads:[~2022-01-05  3:25 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-23  0:21 [PATCH v9 00/15] Function Granular KASLR Alexander Lobakin
2021-12-23  0:21 ` [PATCH v9 01/15] modpost: fix removing numeric suffixes Alexander Lobakin
2021-12-23 16:19   ` Borislav Petkov
2021-12-27 18:22     ` Alexander Lobakin
2021-12-27 21:26       ` Borislav Petkov
2021-12-28 17:03         ` Alexander Lobakin
2022-01-03 13:07   ` Miroslav Benes
2021-12-23  0:21 ` [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search Alexander Lobakin
2021-12-30 11:10   ` Borislav Petkov
2021-12-30 18:31     ` Fāng-ruì Sòng
2022-01-03 13:55       ` Miroslav Benes
2022-01-03 16:06         ` Alexander Lobakin
2022-01-05  3:24           ` Fāng-ruì Sòng [this message]
2022-01-03 16:29     ` Alexander Lobakin
2022-01-03 13:44   ` Miroslav Benes
2021-12-23  0:21 ` [PATCH v9 03/15] kallsyms: Hide layout Alexander Lobakin
2021-12-30 22:36   ` Borislav Petkov
2022-01-03 15:40     ` Alexander Lobakin
2022-01-03 16:59       ` Borislav Petkov
2022-01-05 18:46   ` Borislav Petkov
2021-12-23  0:21 ` [PATCH v9 04/15] arch: introduce ASM function sections Alexander Lobakin
2022-01-17 21:08   ` Borislav Petkov
2022-01-17 21:38     ` Nicolas Pitre
2022-01-17 21:55       ` Borislav Petkov
2021-12-23  0:21 ` [PATCH v9 05/15] x86: support " Alexander Lobakin
2022-01-21 15:08   ` Borislav Petkov
2022-01-26 14:49     ` Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 06/15] x86: decouple ORC table sorting into a separate file Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 07/15] Makefile: Add build and config option for CONFIG_FG_KASLR Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 08/15] x86/tools: Add relative relocs for randomized functions Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 09/15] x86: Add support for function granular KASLR Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 10/15] FG-KASLR: use a scripted approach to handle .text.* sections Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 11/15] x86/boot: allow FG-KASLR to be selected Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 12/15] module: Reorder functions Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 13/15] module: use a scripted approach for FG-KASLR Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 14/15] Documentation: add documentation " Alexander Lobakin
2021-12-23  0:22 ` [PATCH v9 15/15] maintainers: add MAINTAINERS entry " Alexander Lobakin
2021-12-23 15:15 ` [PATCH v9 00/15] Function Granular KASLR Alexander Lobakin
2021-12-23 15:40   ` Peter Zijlstra
2021-12-24  6:38 ` Christoph Hellwig
2021-12-27 18:33   ` Alexander Lobakin
2021-12-30  9:00     ` Christoph Hellwig

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