From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3FBF9E9A02C for ; Wed, 18 Feb 2026 15:21:18 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4fGKwY3008z30hg; Thu, 19 Feb 2026 02:21:17 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1771428077; cv=none; b=ORcvNrSFzRe/uQFX2l2+qCOwTRUq7EYoTUWbndHPuwgabVWpn4UvYIoerkvGueErzduO1ivJwiVD7GJZxVf4RYjLNWx2wcmc5iSiionEPx42QAUD2lOnx3EZEWULXUy4zE1x69pPnaiaFtrZ9G5lp0PDde5fBYfN8Y3n+ewzi5gyw2KlIy3YUyCdUOW5UVUDvxAfN23TgJ/77AePsYEkZc1wMTJdhvArxjA9UWTU2yewZqhyL8QMiWoYRF/kgNZvy0F9PwS03w/81OhDVxIowSxwJ+i885O4zZUHOpmY3eCwZOlTiO68lboiEZoO+jUylo0zgVvvcjFA11D0EseFdQ== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1771428077; c=relaxed/relaxed; bh=sIm+IEOgNc9VlpqTE5y+/ppPLqEHeblG2I6SKqX1NTo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lZ3kCNlZQsJ12SYuNDE0mqWO/yMSoxrDT9JZckB0Yi2I3L5OK4aXIt/oub9nXboxu7euH6VuQspRKRGWtIwvtQoQdfmYC3cOAEas9+HvQkNEP4QDp6mt6oeGUGKYbfMQB5ILOw7Kt1yj3mIGKaCbEZxaFy9NzU54lX64PvvETYhu4glOkZTajjhEMumvyvfphmCked2h2CNqnXh5Tod89x7nGU1C9QCMfWGi2QTQEYJWtNrVZPVawwRzrJiIgmEgpS+m8ElfTUCIASAqrzW2jh8v8aXSvyeFMk0EiKiE4G8JhlCxtumcCa4gI+jIKsxTDJrR5T6fFpOumM9JRb4Pxg== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=ryan.roberts@arm.com; receiver=lists.ozlabs.org) smtp.mailfrom=arm.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=ryan.roberts@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4fGKwW1n7xz2xLv for ; Thu, 19 Feb 2026 02:21:13 +1100 (AEDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B9997339; Wed, 18 Feb 2026 07:20:33 -0800 (PST) Received: from [10.57.81.199] (unknown [10.57.81.199]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 990193F7F5; Wed, 18 Feb 2026 07:20:34 -0800 (PST) Message-ID: <8531da33-a4dc-48ac-abf3-c831d4493afb@arm.com> Date: Wed, 18 Feb 2026 15:20:32 +0000 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/3] randomize_kstack: Unify random source across arches Content-Language: en-GB To: Mark Rutland Cc: kernel test robot , Catalin Marinas , Will Deacon , Huacai Chen , Madhavan Srinivasan , Michael Ellerman , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Kees Cook , "Gustavo A. R. Silva" , Arnd Bergmann , "Jason A. Donenfeld" , Ard Biesheuvel , Jeremy Linton , David Laight , llvm@lists.linux.dev, oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org References: <20260119130122.1283821-4-ryan.roberts@arm.com> <202601210752.6Nsv9et9-lkp@intel.com> <46c7d109-b076-4bb3-9e6e-36c34c546c20@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 21/01/2026 12:32, Mark Rutland wrote: > On Wed, Jan 21, 2026 at 10:52:21AM +0000, Ryan Roberts wrote: >> On 20/01/2026 23:50, kernel test robot wrote: >>> Hi Ryan, >>> >>> kernel test robot noticed the following build warnings: >>> >>> [auto build test WARNING on akpm-mm/mm-everything] >>> [also build test WARNING on linus/master v6.19-rc6 next-20260119] >>> [cannot apply to tip/sched/core kees/for-next/hardening kees/for-next/execve] >>> [If your patch is applied to the wrong git tree, kindly drop us a note. >>> And when submitting patch, we suggest to use '--base' as documented in >>> https://git-scm.com/docs/git-format-patch#_base_tree_information] >>> >>> url: https://github.com/intel-lab-lkp/linux/commits/Ryan-Roberts/randomize_kstack-Maintain-kstack_offset-per-task/20260119-210329 >>> base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything >>> patch link: https://lore.kernel.org/r/20260119130122.1283821-4-ryan.roberts%40arm.com >>> patch subject: [PATCH v4 3/3] randomize_kstack: Unify random source across arches >>> config: x86_64-allmodconfig (https://download.01.org/0day-ci/archive/20260121/202601210752.6Nsv9et9-lkp@intel.com/config) >>> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261) >>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260121/202601210752.6Nsv9et9-lkp@intel.com/reproduce) >>> >>> If you fix the issue in a separate patch/commit (i.e. not just a new version of >>> the same patch/commit), kindly add following tags >>> | Reported-by: kernel test robot >>> | Closes: https://lore.kernel.org/oe-kbuild-all/202601210752.6Nsv9et9-lkp@intel.com/ >>> >>> All warnings (new ones prefixed by >>): >>> >>>>> vmlinux.o: warning: objtool: do_syscall_64+0x2c: call to preempt_count_add() leaves .noinstr.text section >>>>> vmlinux.o: warning: objtool: __do_fast_syscall_32+0x3d: call to preempt_count_add() leaves .noinstr.text section >> >> Hmm, clearly Dave was correct not to rush this through... yuck. I'll take a >> look, but I guess there is no rush if this won't go into -next until shortly >> after -rc1. > > Sorry, I should have checked the entry sequencing more thoroughly when I > reviewed this,. > > From a quick look, I suspect the right thing to do is to pull the call > to add_random_kstack_offset() a bit later in a few cases; after the > entry logic has run, and after instrumentation_begin() (if the arch code > uses that), such that it doesn't matter if this gets instrumented. > > Considering the callers of add_random_kstack_offset(), if we did that: > > * arm64 is fine as-is. > > * loongarch is fine as-is. > > * powerpc's system_call_exception() would need this moved after the > user_exit_irqoff(). Given that function is notrace rather than > noinstr, it looks like there are bigger extant issues here. > > * riscv is fine as-is. > > * s390's __do_syscall() would need this moved after > enter_from_user_mode(). > > * On x86: > - do_int80_emulation() is fine as-is. > - int80_emulation() is fine as-is. > - do_int80_syscall_32() would need this moved after > instrumentation_begin(). > - __do_fast_syscall_32() would need this moved after > instrumentation_begin(). > - do_syscall_64() would need this moved after instrumentation_begin(). Thanks for the detailed suggestions, Mark. I've taken this approach, and assuming perf testing doesn't throw up any issue, I'm going to revert back to using the out-of-line version of prandom_u32_state() and will drop patch 2. Thanks, Ryan > > Mark.