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From: Borislav Petkov <bp@alien8.de>
To: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: 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 12:10:33 +0100	[thread overview]
Message-ID: <Yc2Tqc69W9ukKDI1@zn.tnic> (raw)
In-Reply-To: <20211223002209.1092165-3-alexandr.lobakin@intel.com>

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

  reply	other threads:[~2021-12-30 11:10 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 [this message]
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
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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