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 45FCC27781B for ; Tue, 6 May 2025 10:22:53 +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=1746526974; cv=none; b=kVdKN858lMV7kx3CfJoUdWks4KvGM6sBDriqGKewo3CHVkQqnd6mJnHJe8uiQjWXZ117hRqws+RGwXqoSLQbAYYuvUiDeksSS+L1o0i8SqdjtHkSAiKkjOjN0i+cGsR+O7tyOjCZ24VKmjq0zPwkp1vg1xsbxNb73qwXuCAFJxA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746526974; c=relaxed/simple; bh=GIGiEHsDb/0ScyMMmuJG8LpJ8folWtIkN8Q9wbKcQQw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GUkpAjrO40PK9/PtsZWnOWBc7heIQyjSZp4FMzbOpG96kYtaW6ELyApenm2Uy1tMmjZHb7oyWPbGvWKEb+qjjEzwPFbYQmcJ0VTVbYMhPHkdAkYQJI+oNXXiZm82WBTRq6WE2ArcooMcvRKwt44j/Cr7RnbudH1hi6ulVICCapk= 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 DEA5F1A2D; Tue, 6 May 2025 03:22:42 -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 CC1153F5A1; Tue, 6 May 2025 03:22:48 -0700 (PDT) Message-ID: <3cfcd0c5-79a2-45de-8497-fb95ef834dc1@arm.com> Date: Tue, 6 May 2025 11:22:47 +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: Catalin Marinas , Ard Biesheuvel Cc: 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 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 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); }