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 C9185238C25; Tue, 6 May 2025 10:29:08 +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=1746527348; cv=none; b=jwHJXJ/qEZamY5tX3tJaxftUmUzvyuOC3JAiasOKWF569MPs3UJZWn+GChnpmjyYwxDM8D0JO7aUhXtskVeikJPI3YhHcKMnkz7UrE77SCL8x0bNfkOoYW0Cb6zFeREQ06udbM0W3sSWrIMmrq89OR0CNCBCSuH+CGSIz8ftq5k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746527348; c=relaxed/simple; bh=RvVgQRuS1ioTG27+rPn4EgtU4kcWSyIYqIhT8KufxXs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XOHEN84q81fRdzuhuqQ7Wwm9C0yim0Rg0/d8liAVl6Uxp/E5gRfpMkZkG4MbHy03iCWMtK4t+SpdmZd7eEI+HOr/5AVBqxAUZNBeiAq8HDDYiPrJgr57q8uVOwOl71FS8lIlWbdMKxooO8Cl71bjqpjgbWWITZehFsFHWzJzurc= 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 1012FC4CEE4; Tue, 6 May 2025 10:29:04 +0000 (UTC) Date: Tue, 6 May 2025 11:29:02 +0100 From: Catalin Marinas To: Ryan Roberts Cc: Ard Biesheuvel , 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> <3cfcd0c5-79a2-45de-8497-fb95ef834dc1@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: <3cfcd0c5-79a2-45de-8497-fb95ef834dc1@arm.com> On Tue, May 06, 2025 at 11:22:47AM +0100, Ryan Roberts wrote: > On 06/05/2025 11:17, Catalin Marinas wrote: > > 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. > > Ahh that explains why Yeoreum Yun can't see the issue: > > if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) { > u64 kaslr_seed = kaslr_early_init(fdt, chosen); > > if (kaslr_seed && kaslr_requires_kpti()) > arm64_use_ng_mappings = true; > > kaslr_offset |= kaslr_seed & ~(MIN_KIMG_ALIGN - 1); > } Yeah, you may need this as well for qemu: -object rng-random,filename=/dev/urandom,id=rng0 \ -device virtio-rng-pci,rng=rng0 \ BTW, some architectures have RO_DATA immediately after _sdata but for us it messes up some of the contig mappings, so the safest is to move the variable to the .data section. -- Catalin