From: "Fāng-ruì Sòng" <maskray@google.com>
To: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: 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>,
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>,
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: Thu, 30 Dec 2021 10:31:27 -0800 [thread overview]
Message-ID: <CAFP8O3K1mkiCGMTEeuSifZtr2piHsKTjP5TOA25nqpv2SrbzYQ@mail.gmail.com> (raw)
In-Reply-To: <Yc2Tqc69W9ukKDI1@zn.tnic>
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
>
> nuke?
>
> I think you wanna say something about avoiding position-based search if
> toolchain supports -z ...
>
> > Position-based search, which means that if we have several symbols
> > with the same name, we additionally need to provide an "index" of
> > the desired symbol, is fragile. Par exemple, it breaks when two
> ^^^^^^^^^^^^
>
> We already have hard time with the English in commit messages, let's
> avoid the French pls.
>
> > 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).
> > Check for its availability and always prefer when the livepatching
> > is on.
>
> Why only then?
>
> It looks to me like we want this unconditionally, no?
>
> > This needs a little adjustment to the modpost to make it
> > strip suffixes before adding exports.
> >
> > depmod needs some treatment as well, tho its false-positibe warnings
>
> Unknown word [false-positibe] in commit message, suggestions:
> ['false-positive', 'false-positioned', 'prepositional']
>
> Please introduce a spellchecker into your patch creation workflow.
>
> > about unknown symbols are harmless and don't alter the return code.
> > And there is a bunch more livepatch code to optimize-out after
> > introducing this, but let's leave it for later.
>
> ...
>
> > @@ -171,17 +173,21 @@ static int klp_find_object_symbol(const char *objname, const char *name,
> >
> > /*
> > * Ensure an address was found. If sympos is 0, ensure symbol is unique;
> > - * otherwise ensure the symbol position count matches sympos.
> > + * otherwise ensure the symbol position count matches sympos. If the LD
> > + * `-z unique` flag is enabled, sympos checks are not relevant.
> ^^^^^^^^^^^
>
> -z unique-symbol
>
> > */
> > - if (args.addr == 0)
> > + if (args.addr == 0) {
> > pr_err("symbol '%s' not found in symbol table\n", name);
> > - else if (args.count > 1 && sympos == 0) {
> > + } else if (IS_ENABLED(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL)) {
> > + goto out_ok;
>
> This is silly - just do it all here.
>
> > + } else if (args.count > 1 && sympos == 0) {
> > pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
> > name, objname);
> > } else if (sympos != args.count && sympos > 0) {
> > pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
> > sympos, name, objname ? objname : "vmlinux");
> > } else {
> > +out_ok:
> > *addr = args.addr;
> > return 0;
> > }
>
> Looks straight-forward otherwise but I'm no livepatcher so I'd prefer if
> they have a look too.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
>
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.)
next prev parent reply other threads:[~2021-12-30 18:31 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 [this message]
2022-01-03 13:55 ` Miroslav Benes
2022-01-03 16:06 ` Alexander Lobakin
2022-01-05 3:24 ` Fāng-ruì Sòng
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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