From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 24394212B04; Tue, 6 May 2025 10:17:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746526663; cv=none; b=RIOnHNEmNHf8Y9GI9R/yJw6Fd5wHnRN24V+O00o/RCUpZeDYECBARUQQHQE/PVJrg9W009DfIEh6Ri1TNi9Fp+deQGw8t9u3CTNyovBcM4hGDlM3WLWfTQmzBFT1BVDayUsJ+TpOCe2Ar/qu/eJfv94q7J7PrYMHs6+uMbpnbdE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746526663; c=relaxed/simple; bh=IX+PP8LlX1bH0FcoepRyMQgD9hjjLVq86Rm6toSU0G0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mxRiCQlZuU0G2YXLSOS5EaSxBP0oGyYWJks3OsdqYZ4aHLCpWRMallsFwb/W1RUQdhDo3fphUOti8tuY5YnTvdtQ9pSb4b8Q8c8r4nEx5LtJFMvI6Lic8D4Y0F0apGX54FP5DHEBHB9iD7G9KZHQXEqAFDGt56BtJJyq3oYFvMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8494CC4CEE4; Tue, 6 May 2025 10:17:39 +0000 (UTC) Date: Tue, 6 May 2025 11:17:37 +0100 From: Catalin Marinas To: Ard Biesheuvel Cc: Ryan Roberts , Yeoreum Yun , will@kernel.org, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, morbo@google.com, justinstitt@google.com, broonie@kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, shameerali.kolothum.thodi@huawei.com, james.morse@arm.com, hardevsinh.palaniya@siliconsignals.io, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH v2] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation Message-ID: References: <20250502180412.3774883-1-yeoreum.yun@arm.com> <174626735218.2189871.10298017577558632540.b4-ty@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, May 06, 2025 at 11:41:05AM +0200, Ard Biesheuvel wrote: > On Tue, 6 May 2025 at 10:16, Ryan Roberts wrote: > > On 06/05/2025 09:09, Yeoreum Yun wrote: > > >> On Sat, May 03, 2025 at 09:23:27PM +0100, Yeoreum Yun wrote: > > >>>> On Sat, May 03, 2025 at 11:16:12AM +0100, Catalin Marinas wrote: > > >>>>> On Fri, 02 May 2025 19:04:12 +0100, Yeoreum Yun wrote: > > >>>>>> create_init_idmap() could be called before .bss section initialization > > >>>>>> which is done in early_map_kernel(). > > >>>>>> Therefore, data/test_prot could be set incorrectly by PTE_MAYBE_NG macro. > > >>>>>> > > >>>>>> PTE_MAYBE_NG macro set NG bit according to value of "arm64_use_ng_mappings". > > >>>>>> and this variable places in .bss section. > > >>>>>> > > >>>>>> [...] > > >>>>> > > >>>>> Applied to arm64 (for-next/fixes), with some slight tweaking of the > > >>>>> comment, thanks! > > >>>>> > > >>>>> [1/1] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation > > >>>>> https://git.kernel.org/arm64/c/12657bcd1835 > > >>>> > > >>>> I'm going to drop this for now. The kernel compiled with a clang 19.1.5 > > >>>> version I have around (Debian sid) fails to boot, gets stuck early on: > > >>>> > > >>>> $ clang --version > > >>>> Debian clang version 19.1.5 (1) > > >>>> Target: aarch64-unknown-linux-gnu > > >>>> Thread model: posix > > >>>> InstalledDir: /usr/lib/llvm-19/bin > > >>>> > > >>>> I didn't have time to investigate, disassemble etc. I'll have a look > > >>>> next week. > > >>> > > >>> Just for your information. > > >>> When I see the debian package, clang 19.1.5-1 doesn't supply anymore: > > >>> - https://ftp.debian.org/debian/pool/main/l/llvm-toolchain-19/ > > >>> > > >>> and the default version for sid is below: > > >>> > > >>> $ clang-19 --version > > >>> Debian clang version 19.1.7 (3) > > >>> Target: aarch64-unknown-linux-gnu > > >>> Thread model: posix > > >>> InstalledDir: /usr/lib/llvm-19/bin > > >>> > > >>> When I tested with above version with arm64-linux's for-next/fixes > > >>> including this patch. it works well. > > >> > > >> It doesn't seem to be toolchain related. It fails with gcc as well from > > >> Debian stable but you'd need some older CPU (even if emulated, e.g. > > >> qemu). It fails with Cortex-A72 (guest on Raspberry Pi 4) but not > > >> Neoverse-N2. Also changing the annotation from __ro_after_init to > > >> __read_mostly also works. > > > > I think this is likely because __ro_after_init is also "ro before init" - i.e. > > if you try to write to it in the PI code an exception is generated due to it > > being mapped RO. Looks like early_map_kernel() is writiing to it. > > Indeed. > > > I've noticed a similar problem in the past and it would be nice to fix it so > > that PI code maps __ro_after_init RW. > > The issue is that the store occurs via the ID map, which only consists > of one R-X and one RW- section. I'm not convinced that it's worth the > hassle to relax this. > > If moving the variable to .data works, then let's just do that. Good to know there's no other more serious issue. I'll move this variable to __read_mostly. It seems to fail in early_map_kernel() if RANDOMIZE_BASE is enabled. -- Catalin