From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2C6BE481249; Wed, 21 Jan 2026 12:32:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768998742; cv=none; b=dc8MKACPUhy0bv2AcZU6lnic8l3UojjqYuEYT+VEppTFy8ot9tr8k/SfN5jihAzkxHsqKq0tL8jRUsw70B8iWCQKZR3Yeso7WrAA/SOWYTvx+ugICU69LHhDSgsaBNW7K6JUx7jNWEL9gLQ4wRYAdOfKZiLH1TPh7OHot5rqndM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768998742; c=relaxed/simple; bh=FELHx54kV3W/qnATluFqgshAxI/luUBfj25peQmvX7A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ekXg4nWnRQzqXq02K50bjhIA5GL17ihNE3HfOFbo8mZdD5WiReJxm7CmmD3mvt25AIqARb7blq/qu4faDyCrOh9qH4AUYT3TJd5FF/3SSje/0wsqM6Acva7LXo71JMduqrhviighDSJDV/23ZysIkfC/Om8gii5oBgRyoWzlHSk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 D87A81476; Wed, 21 Jan 2026 04:32:12 -0800 (PST) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 16A163F740; Wed, 21 Jan 2026 04:32:13 -0800 (PST) Date: Wed, 21 Jan 2026 12:32:08 +0000 From: Mark Rutland To: Ryan Roberts 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 Subject: Re: [PATCH v4 3/3] randomize_kstack: Unify random source across arches Message-ID: References: <20260119130122.1283821-4-ryan.roberts@arm.com> <202601210752.6Nsv9et9-lkp@intel.com> <46c7d109-b076-4bb3-9e6e-36c34c546c20@arm.com> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46c7d109-b076-4bb3-9e6e-36c34c546c20@arm.com> 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(). Mark.