linux-kernel - Re: [PATCH v3 42/64] kbuild,x86: Fix special section module permissions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250630073144.GE1613200@noisy.programming.kicks-ass.net>
Date: Mon, 30 Jun 2025 09:31:44 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	live-patching@...r.kernel.org, Song Liu <song@...nel.org>,
	laokz <laokz@...mail.com>, Jiri Kosina <jikos@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Weinan Liu <wnliu@...gle.com>,
	Fazla Mehrab <a.mehrab@...edance.com>,
	Chen Zhongjin <chenzhongjin@...wei.com>,
	Puranjay Mohan <puranjay@...nel.org>,
	Dylan Hatch <dylanbhatch@...gle.com>,
	Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH v3 42/64] kbuild,x86: Fix special section module
 permissions

On Fri, Jun 27, 2025 at 10:34:15AM -0700, Josh Poimboeuf wrote:
> On Fri, Jun 27, 2025 at 12:53:28PM +0200, Peter Zijlstra wrote:
> > On Thu, Jun 26, 2025 at 04:55:29PM -0700, Josh Poimboeuf wrote:
> > > An upcoming patch will add the SHF_MERGE flag to x86 __jump_table and
> > > __bug_table so their entry sizes can be defined in inline asm.
> > > 
> > > However, those sections have SHF_WRITE, which the Clang linker (lld)
> > > explicitly forbids combining with SHF_MERGE.
> > > 
> > > Those sections are modified at runtime and must remain writable.  While
> > > SHF_WRITE is ignored by vmlinux, it's still needed for modules.
> > > 
> > > To work around the linker interference, remove SHF_WRITE during
> > > compilation and restore it after linking the module.
> > 
> > This is vile... but I'm not sure I have a better solution.
> > 
> > Eventually we should get the toolchains fixed, but we can't very well
> > mandate clang-21+ to build x86 just yet.
> 
> Yeah, I really hate this too.  I really tried to find something better,
> including mucking with the linker script, but this was unfortunately the
> only thing that worked.
> 
> Though, looking at it again, I realize we can localize the pain to Clang
> (and the makefile) by leaving the code untouched and instead strip
> SHF_WRITE before the link and re-add it afterwards.  Then we can tie
> this horrible hack to specific Clang versions when it gets fixed.

Oh yeah, that might be nicer indeed!