Re: [PATCH v10 10/15] FG-KASLR: use a scripted approach to handle .text.* sections

From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Lobakin <alexandr.lobakin@intel.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>,
	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>,
	Christoph Hellwig <hch@lst.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
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	Andy Lutomirski <luto@kernel.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,
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	llvm@lists.linux.dev
Subject: Re: [PATCH v10 10/15] FG-KASLR: use a scripted approach to handle .text.* sections
Date: Mon, 14 Feb 2022 12:34:34 +0100	[thread overview]
Message-ID: <20220214113434.5256-1-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <20220211153706.GW23216@worktop.programming.kicks-ass.net>

From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 11 Feb 2022 16:37:06 +0100

> On Wed, Feb 09, 2022 at 07:57:47PM +0100, Alexander Lobakin wrote:
> > +sub read_sections {
> > +	open(my $fh, "\"$readelf\" -SW \"$file\" 2>/dev/null |")
> > +		or die "$0: ERROR: failed to execute \"$readelf\": $!";
> > +
> > +	while (<$fh>) {
> > +		my $name;
> > +		my $align;
> > +		chomp;
> > +
> > +		($name, $align) = $_ =~ /^\s*\[[\s0-9]*\]\s*(\.\S*)\s*[A-Z]*\s*[0-9a-f]{16}\s*[0-9a-f]*\s*[0-9a-f]*\s*[0-9a-f]*\s*[0-9a-f]{2}\s*[A-Z]{2}\s*[0-9]\s*[0-9]\s*([0-9]*)$/;
> 
> Is there really no readable way to write this?

I'm no regexp master, so I'd be glad if someone could help improve
this :D I only tried to optimize it using online tools, and they
eventually didn't help.
It could probably be replaced with a pipe to `cut` or `tr`, I'll
take a look a bit later if there won't be any other proposals.

> 
> > +
> > +		if (!defined($name)) {
> > +			next;
> > +		}
> > +
> > +		## Clang 13 onwards emits __cfi_check_fail only on final
> > +		## linking, so it won't appear in .o files and will be
> > +		## missing in @sections. Add it manually to prevent
> > +		## spawning orphans.
> > +		if ($name eq ".text.__cfi_check_fail") {
> > +			$has_ccf = 1;
> > +		}
> 
> How is that relevant, x86-64 doesn't and won't do clang-cfi.

1. One of my test cases was based on Sami's ClangCFI x86 series from
   LKML (the one that was getting patched by objtool :P).
2. ClangCFI is present on ARM64 and it can receive FG-KASLR in a
   future, why not make it work together from the start?

Re "won't do" -- sorry for trying to hijack this thread a bit, but
did I miss something? The last comments I've read were that LLVM
tools need to change their approach for CFI on x86, and Sami went
redo it, but I can't recall any "life-time" nacks.

Thanks,
Al