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 9B60417B4EC for ; Tue, 6 May 2025 10:08:44 +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=1746526126; cv=none; b=sTfuxzsSsaselJfbgxzSuU/g3Quaw2bGxzZMSUmq7WUyQ9dfPO6ajN7N4mSK6t9bUejugZR9nULvN1kas1522dikKdb8Y+qHzeys1+XUtVErCl5a8t32qacfIUDUrH8w9D+k6yk3YJPdpq9/mHNhvg9w/mP68g2QPX1ray5iDNk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746526126; c=relaxed/simple; bh=U/sHJ0rllBZTo4yrsxKaCC6IiisHumKHo3x1yJ7lEeI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ir9NA/mYm+/c9sOQOJHWd3DhI7kXBHBM/anU1fn/Jr/nmqp5r9KhkhcMIMrk9y3wIcimP1v0vxlzuMK6RPvQI4NIQPZs/e1LnWGdkq3pU8aAxxCx0PidmotJpUJi8tYk21ojeNBQYPhBnWw73K6UIzkiOF5ImsBaMTAHO/4ZExA= 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 3F4E2113E; Tue, 6 May 2025 03:08:34 -0700 (PDT) Received: from [10.57.93.118] (unknown [10.57.93.118]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 799073F5A1; Tue, 6 May 2025 03:08:40 -0700 (PDT) Message-ID: Date: Tue, 6 May 2025 11:08:38 +0100 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation Content-Language: en-GB To: Ard Biesheuvel Cc: Yeoreum Yun , Catalin Marinas , 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 References: <20250502180412.3774883-1-yeoreum.yun@arm.com> <174626735218.2189871.10298017577558632540.b4-ty@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 06/05/2025 10:41, Ard Biesheuvel wrote: > On Tue, 6 May 2025 at 10:16, Ryan Roberts wrote: >> >> On 06/05/2025 09:09, Yeoreum Yun wrote: >>> Hi Catalin, >>> >>>> On Sat, May 03, 2025 at 09:23:27PM +0100, Yeoreum Yun wrote: >>>>> Hi Catalin, >>>>> >>>>>> 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. Yeah, fair enough.