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 B49C939B4A3; Mon, 1 Jun 2026 10:43:40 +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=1780310626; cv=none; b=V33/DQ5IvvfWFwqSkzOXns/HyaYqVNjhPlvSiuZvPGllqbTIrUfJHTiBO7v5DhQP01ubXGrXaNBKokrsiTfthK6p2qsoqY2nQ4h8HuLOcksnSI8GxnrmJ7Fg+NTKANhSlxKN7KSQE0pb/ow1bD8ePug8CCAG+n4ACJeVmEA+C0M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780310626; c=relaxed/simple; bh=C3+Nupy9epvTU9YJN+UUOeTEoo2XErmrS9cELXLEaTU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JbQrXa7OQvpM1vvKXzRRvSUWPWOH0x00Km/5/aH7WpU1E6GBju3PSW/x+yCngO4MMleVqj3aCnzjemTUy3Np9jYcVH2H5dxX9uebLe/mlJG4BHD8crQ3EcATSPPbRqUCYpHycx/gJxzU+MDh8bwU916kGJ/+1KPi6yG2rOC/oos= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=ATGD2KEF; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="ATGD2KEF" 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 EB1D41516; Mon, 1 Jun 2026 03:43:34 -0700 (PDT) Received: from [10.57.94.8] (unknown [10.57.94.8]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 38E4D3F905; Mon, 1 Jun 2026 03:43:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1780310619; bh=C3+Nupy9epvTU9YJN+UUOeTEoo2XErmrS9cELXLEaTU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ATGD2KEFk9zH6A/3/wbmsLo8Bk16zruKAja2MWpstRHrcKrUHTc7cCqmaTsy1kze4 vG+kAYpgRYGrfxsVM+k07lFcID8aETdcpIWAaY6POEOlyHhT7SAbyCaNPXgf688bb2 NWAccF9tR54IJl/TxpZC5Vs/Yx5VmFz06QrmL7VQ= Message-ID: Date: Mon, 1 Jun 2026 12:43:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 15/15] arm64: mm: Unmap kernel data/bss entirely from the linear map To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , Mike Rapoport , David Hildenbrand , Andrew Morton , Jann Horn , linux-mm@kvack.org, linux-hardening@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org References: <20260529150150.1670604-17-ardb+git@google.com> <20260529150150.1670604-32-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260529150150.1670604-32-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 29/05/2026 17:02, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > The linear aliases of the kernel text and rodata are also mapped > read-only in the linear map. Given that the contents of these regions > are mostly identical to the version in the loadable image, mapping them > read-only and leaving their contents visible is a reasonable hardening > measure. > > Data and bss, however, are now also mapped read-only but the contents of > these regions are more likely to contain data that we'd rather not leak. > So let's unmap these entirely in the linear map when the kernel is > running normally. > > When going into hibernation or waking up from it, these regions need to > be mapped, so map the region initially, and toggle the valid bit so > map/unmap the region as needed. s/so map/to map/? Also not sure what "initially" is referring to here. Otherwise: Reviewed-by: Kevin Brodsky I don't know much about hibernation though, would be good for someone knowledgeable to have a look. - Kevin > Doing so is required because pages covering the kernel image are marked > as PageReserved, and therefore disregarded for snapshotting by the > hibernate logic unless they are mapped. > > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/mm/mmu.c | 45 ++++++++++++++++++-- > 1 file changed, 41 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 7b18dc2f1721..07a6fa210171 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -24,6 +24,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1056,6 +1057,29 @@ static void __init __map_memblock(phys_addr_t start, phys_addr_t end, > end - start, prot, early_pgtable_alloc, flags); > } > > +static void mark_linear_data_alias_valid(bool valid) > +{ > + set_memory_valid((unsigned long)lm_alias(__init_end), > + (unsigned long)(__bss_stop - __init_end) / PAGE_SIZE, > + valid); > +} > + > +static int arm64_hibernate_pm_notify(struct notifier_block *nb, > + unsigned long mode, void *unused) > +{ > + switch (mode) { > + default: > + break; > + case PM_POST_HIBERNATION: > + mark_linear_data_alias_valid(false); > + break; > + case PM_HIBERNATION_PREPARE: > + mark_linear_data_alias_valid(true); > + break; > + } > + return 0; > +} > + > void __init mark_linear_text_alias_ro(void) > { > /* > @@ -1064,6 +1088,21 @@ void __init mark_linear_text_alias_ro(void) > update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text), > (unsigned long)__init_begin - (unsigned long)_text, > PAGE_KERNEL_RO); > + > + /* > + * Register a PM notifier to remap the linear alias of data/bss as > + * valid read-only before hibernation. This is needed because the > + * snapshot logic disregards PageReserved pages (such as the ones > + * covering the kernel image) unless they are mapped in the linear > + * map. > + */ > + if (IS_ENABLED(CONFIG_HIBERNATION)) { > + static struct notifier_block nb = { > + .notifier_call = arm64_hibernate_pm_notify > + }; > + > + register_pm_notifier(&nb); > + } > } > > #ifdef CONFIG_KFENCE > @@ -1193,10 +1232,8 @@ static void __init map_mem(void) > flags); > } > > - /* Map the kernel data/bss read-only in the linear map */ > - __map_memblock(init_end, kernel_end, PAGE_KERNEL_RO, flags); > - flush_tlb_kernel_range((unsigned long)lm_alias(__init_end), > - (unsigned long)lm_alias(__bss_stop)); > + /* Map the kernel data/bss as invalid in the linear map */ > + mark_linear_data_alias_valid(false); > } > > void mark_rodata_ro(void)