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Date: Mon, 3 Jan 2022 17:29:31 +0100 From: Alexander Lobakin <alexandr.lobakin@...el.com> To: Borislav Petkov <bp@...en8.de> Cc: Alexander Lobakin <alexandr.lobakin@...el.com>, linux-hardening@...r.kernel.org, x86@...nel.org, Jesse Brandeburg <jesse.brandeburg@...el.com>, Kristen Carlson Accardi <kristen@...ux.intel.com>, Kees Cook <keescook@...omium.org>, Miklos Szeredi <miklos@...redi.hu>, Ard Biesheuvel <ardb@...nel.org>, Tony Luck <tony.luck@...el.com>, Bruce Schlobohm <bruce.schlobohm@...el.com>, Jessica Yu <jeyu@...nel.org>, kernel test robot <lkp@...el.com>, Miroslav Benes <mbenes@...e.cz>, Evgenii Shatokhin <eshatokhin@...tuozzo.com>, Jonathan Corbet <corbet@....net>, Masahiro Yamada <masahiroy@...nel.org>, Michal Marek <michal.lkml@...kovi.net>, Nick Desaulniers <ndesaulniers@...gle.com>, Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann <arnd@...db.de>, Josh Poimboeuf <jpoimboe@...hat.com>, Nathan Chancellor <nathan@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Marios Pomonis <pomonis@...gle.com>, Sami Tolvanen <samitolvanen@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org, live-patching@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search From: Borislav Petkov <bp@...en8.de> Date: Thu, 30 Dec 2021 12:10:33 +0100 > 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 ... Correct. A "vocabulary fail" moment. > > > 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? To be as least invasive as possible for now. We can turn it on unconditionally after a while. LLD doesn't support it and this and there are some different opinions about unique-symbol in general. Maybe FG-KASLR builds will reveal that some of the concerns are true, who knows. It wouldn't need to get turned off back again then. > > > 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. It's here, but refused to work this time or so <O> I have definitely run checkpatch with codespell against the series I can't recall any reported typos. > > > 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. Yeah, a "big brain" moment from me. Or even reset sympos to 0 when unique-symbol is enabled, like Mirek suggests. > > > + } 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 Thanks, Al
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