From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "Alexander Lobakin" <alexandr.lobakin@intel.com>,
"Fāng-ruì Sòng" <maskray@google.com>,
linux-hardening@vger.kernel.org, x86@kernel.org,
"Borislav Petkov" <bp@alien8.de>,
"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>,
"Miroslav Benes" <mbenes@suse.cz>,
"Evgenii Shatokhin" <eshatokhin@virtuozzo.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Masahiro Yamada" <masahiroy@kernel.org>,
"Michal Marek" <michal.lkml@markovi.net>,
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"Thomas Gleixner" <tglx@linutronix.de>,
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"Masami Hiramatsu" <mhiramat@kernel.org>,
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"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,
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llvm@lists.linux.dev
Subject: Re: [PATCH v10 02/15] livepatch: avoid position-based search if `-z unique-symbol` is available
Date: Mon, 14 Feb 2022 13:24:33 +0100 [thread overview]
Message-ID: <20220214122433.288910-1-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <20220211183529.q7qi2qmlyuscxyto@treble>
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Fri, 11 Feb 2022 10:35:29 -0800
> On Fri, Feb 11, 2022 at 10:05:02AM -0800, Fāng-ruì Sòng wrote:
> > On Fri, Feb 11, 2022 at 9:41 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > >
> > > On Wed, Feb 09, 2022 at 07:57:39PM +0100, Alexander Lobakin wrote:
> > > > Position-based search, which means that if there are several symbols
> > > > with the same name, the user needs to additionally provide the
> > > > "index" of a desired symbol, is fragile. For example, it breaks
> > > > when two symbols with the same name are located in different
> > > > sections.
> > > >
> > > > Since a while, LD has a flag `-z unique-symbol` which appends
> > > > numeric suffixes to the functions with the same name (in symtab
> > > > and strtab). It can be used to effectively prevent from having
> > > > any ambiguity when referring to a symbol by its name.
> > >
> > > In the patch description can you also give the version of binutils (and
> > > possibly other linkers) which have the flag?
> >
> > GNU ld>=2.36 supports -z unique-symbol. ld.lld doesn't support -z unique-symbol.
> >
> > I subscribe to llvm@lists.linux.dev and happen to notice this message
> > (can't keep up with the changes...)
> > I am a bit concerned with this option and replied last time on
> > https://lore.kernel.org/r/20220105032456.hs3od326sdl4zjv4@google.com
> >
> > My full reasoning is on
> > https://maskray.me/blog/2020-11-15-explain-gnu-linker-options#z-unique-symbol
>
> Ah, right. Also discussed here:
>
> https://lore.kernel.org/all/20210123225928.z5hkmaw6qjs2gu5g@google.com/T/#u
> https://lore.kernel.org/all/20210125172124.awabevkpvq4poqxf@treble/
>
> I'm not qualified to comment on LTO/PGO stability issues, but it doesn't
> sound good. And we want to support livepatch for LTO kernels.
>
> Also I realized that this flag would have a negative effect on
> kpatch-build, as it currently does its analysis on .o files. So it
> would have to figure out how to properly detect function renames, to
> avoid patching the wrong function for example.
>
> And if LLD doesn't plan to support the flag then it will be a headache
> for livepatch (and the kernel in general) to deal with the divergent
> configs.
I'm always down with replacing any of the parts, I'm just not
familiar with any other ways of approaching this without huge diffs.
I've read Fāng-ruì's blogpost previously and there's a possible
replacement described there, but I dunno how to approach it.
And them Miroslav just told me that unique-symbol should work just
fine and I can go with it.
So I asked here prevously and ask once again for any hints regarding
some other ways :p
>
> One idea I mentioned before, it may be worth exploring changing the "F"
> in FGKASLR to "File" instead of "Function". In other words, only
> shuffle at an object-file granularity. Then, even with duplicates, the
> <file+function> symbol pair doesn't change in the symbol table. And as
> a bonus, it should help FGKASLR i-cache performance, significantly.
Yeah, I keep that in mind. However, this wouldn't solve the
duplicate static function names problem, right?
Let's say you have a static function f() in file1 and f() in file2,
then the layout each boot can be
.text.file1 or .text.file2
f() f()
.text.file2 .text.file1
f() f()
and position-based search won't work anyway, right?
>
> --
> Josh
Thanks,
Al
next prev parent reply other threads:[~2022-02-14 12:25 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-09 18:57 [PATCH v10 00/15] Function Granular KASLR Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 01/15] modpost: fix removing numeric suffixes Alexander Lobakin
2022-05-03 0:57 ` Masahiro Yamada
2022-05-03 7:31 ` Petr Mladek
2022-05-23 18:04 ` Masahiro Yamada
2022-05-24 11:33 ` Alexander Lobakin
2022-05-24 13:40 ` Masahiro Yamada
2022-02-09 18:57 ` [PATCH v10 02/15] livepatch: avoid position-based search if `-z unique-symbol` is available Alexander Lobakin
2022-02-11 17:41 ` Josh Poimboeuf
2022-02-11 18:05 ` Fāng-ruì Sòng
2022-02-11 18:35 ` Josh Poimboeuf
2022-02-14 12:24 ` Alexander Lobakin [this message]
2022-02-14 18:10 ` Josh Poimboeuf
2022-02-16 20:32 ` Joe Lawrence
2022-02-16 22:13 ` Josh Poimboeuf
2022-02-16 15:15 ` Miroslav Benes
2022-02-16 20:01 ` Josh Poimboeuf
2022-02-18 16:31 ` Alexander Lobakin
2022-02-18 20:08 ` Josh Poimboeuf
2022-02-14 12:14 ` Alexander Lobakin
2022-02-14 18:57 ` Josh Poimboeuf
2022-02-16 15:06 ` Miroslav Benes
2022-02-16 19:57 ` Josh Poimboeuf
2022-02-17 7:45 ` Miroslav Benes
2022-02-09 18:57 ` [PATCH v10 03/15] kallsyms: randomize /proc/kallsyms output order Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 04/15] arch: introduce asm function sections Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 05/15] x86: support " Alexander Lobakin
2022-02-11 15:45 ` Peter Zijlstra
2022-02-14 11:49 ` Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 06/15] x86: decouple ORC table sorting into a separate file Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 07/15] Makefile: add config options and build scripts for FG-KASLR Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 08/15] x86/tools: Add relative relocs for randomized functions Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 09/15] x86: Add support for function granular KASLR Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 10/15] FG-KASLR: use a scripted approach to handle .text.* sections Alexander Lobakin
2022-02-11 15:37 ` Peter Zijlstra
2022-02-14 11:34 ` Alexander Lobakin
2022-02-14 11:59 ` Peter Zijlstra
2022-02-14 12:30 ` Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 11/15] x86/boot: allow FG-KASLR to be selected Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 12/15] module: add arch-indep FG-KASLR for randomizing function layout Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 13/15] module: use a scripted approach for FG-KASLR Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 14/15] Documentation: add documentation " Alexander Lobakin
2022-02-09 18:57 ` [PATCH v10 15/15] maintainers: add MAINTAINERS entry " Alexander Lobakin
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