linux-kernel - Re: [PATCH v2 42/62] kbuild,x86: Fix module permissions for __jump_table and __bug

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: <cv2xosjolcau7n3poyymo3yodhl4cokwmju53d3rwfsqhkbqym@rsvd5oqqhczk>
Date: Wed, 4 Jun 2025 17:22:11 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.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>, Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH v2 42/62] kbuild,x86: Fix module permissions for
 __jump_table and __bug_table

On Mon, May 26, 2025 at 01:06:34PM +0200, Peter Zijlstra wrote:
> On Fri, May 09, 2025 at 01:17:06PM -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.
> 
> *groan*
> 
> This and the following patches marking a whole bunch of sections M,
> seems to suggest you're going to rely on sh_entsize actually working.
> 
> There was an ld.lld bug, and IIRC you need to enforce llvm-20 or later
> if you want this to be so.

Hm, ISTR this working with clang 18, I'll go test that again.

-- 
Josh