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 6C8BA27585E; Tue, 6 May 2025 10:12:55 +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=1746526377; cv=none; b=Ylq6ta5Xp06UVPxKmdN4sJ0o00jLM84p6PkpIybBAbSp/sE4nhaJK7XBFwMxVAExPBL8QeHX0qrGh5XiUh1oiPRX6Ksxi84Ar+X9hTXTHiRD2UoopKi0KE510oWp0MM9rzsQPRXceLKsXoWV/SJDqjNEcr8xPJRfejdKaMG6XK0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746526377; c=relaxed/simple; bh=Ngr7JnvUFx8dNX6/o6M3TBbzJOOYusnzmhNr5ZlMzrE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=l36z5zKCrn6MMrBNHrD4FWVYm0KacCBZG7VCZnqBIJIqLE7AiczVf+KRzRKv0TD5+SMRcqBOu2GMJrLOOWewy+dAJ8Sya/+5XV9mZnSbF98X69WVnsPmG38VFuGiZzkuMS9ezKGd2YIhsPQe9Dyj0l09LBDndCuXsFK5NUrYbkE= 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 BC39FC4CEE4; Tue, 6 May 2025 10:12:52 +0000 (UTC) Date: Tue, 6 May 2025 11:12:50 +0100 From: Catalin Marinas To: Yeoreum Yun Cc: Ryan Roberts , 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, ardb@kernel.org, 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 09:53:57AM +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: [...] > Personally, I don't believe this because the create_init_idmap() > maps the the .rodata section with PAGE_KERNEL pgprot > from __initdata_begin to _end. > > and at the mark_readonly() the pgprot is changed to PAGE_KERNEL_RO > But, arm64_use_ng_mappings is accessed with write before mark_readonly() > only via smp_cpus_done(). > > JFYI here is map information: > > // mark_readlonly() changes to ro perm below ranges: > ffff800081b30000 g .rodata 0000000000000000 __start_rodata > ffff800082560000 g .rodata.text 0000000000000000 __init_begin > > // create_init_idmap() maps below range with PAGE_KERNEL. > ffff8000826d0000 g .altinstructions 0000000000000000 __initdata_begin > ffff800082eb0000 g .bss 0000000000000000 _end > > ffff8000824596d0 g O .rodata 0000000000000001 arm64_use_ng_mappings So arm64_use_ng_mappings is mapped as read-only since .rodata is before __initdata_begin. -- Catalin