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 4DF693B52E9; Fri, 29 May 2026 08:29:55 +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=1780043398; cv=none; b=aNVYKZOFMM0DC4lF/y5P+3Y65aAI7aj9BfStCXAsf7jKGlXAjOOhe2llvT1TeufQI5oq+wlMD6XX/DmxhsWnyXPyqP7+5Q+uuv1wL7KPMHvHYCEyESWuWOJWohyXnh4iPEJCJBi6JZgN9UMlxzr++EKwEH4jYtZzJOjb3cNmVYk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780043398; c=relaxed/simple; bh=LpGrRJmNWPcHaRlBV5w3lZl9XAW9wUfZkoWTWBy1nFU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YYgV7rxKPpX6YV4JQxNZPsDuMLHrxh/OAhM9lcwqUlqVr/9aAF3LmgAS4/X1RSJAMzO17FCukVbe1E7CGPnhBrLixF1hxwmPmIfU1kpzevWqZDxlLZyHqoTf3hIVd1cedOmK8Om67QaJJXGIRFu9kar8HRfmJVimvxyM7N3NDsU= 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=lsoxhOxi; 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="lsoxhOxi" 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 A4B8632E5; Fri, 29 May 2026 01:29:49 -0700 (PDT) Received: from [10.57.91.162] (unknown [10.57.91.162]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6892D3F632; Fri, 29 May 2026 01:29:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1780043394; bh=LpGrRJmNWPcHaRlBV5w3lZl9XAW9wUfZkoWTWBy1nFU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lsoxhOxibEyJ5lHCGdr76YlKUY9UPjWMsbTlSjV42xLs3UC50ylcZ0jNiRAuX0LGv ROtFFBK8bd+Dt4HWaxYhwBs7wmthKtbXrEd5RFcjHrtddOa2uIt79pP/Ld+WjmS07W 9VlU1fIqvgS6mSD3ptke3Hza5XxLJoHl2kJtRHTA= Message-ID: <22042b98-cfcc-428e-bb08-ebcfe785eb69@arm.com> Date: Fri, 29 May 2026 10:29:47 +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 v6 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: <20260526175846.2694125-17-ardb+git@google.com> <20260526175846.2694125-32-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260526175846.2694125-32-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 26/05/2026 19:59, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > The linear aliases of the kernel text and rodata are mapped read-only in > the linear map as well. 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. (While the hibernation snapshot logic > seems able to map inaccessible pages as needed, it currently disregards > non-present pages entirely.) I'm not sure I understand this, is there something wrong with the kernel_page_present() check in safe_copy_page()? > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/mm/mmu.c | 39 +++++++++++++++++--- > 1 file changed, 34 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index e7ca53d20b87..cb00e42abbe1 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 remap_linear_data_alias(bool unmap) > +{ > + set_memory_valid((unsigned long)lm_alias(__init_end), > + (unsigned long)(__bss_stop - __init_end) / PAGE_SIZE, > + !unmap); > +} > + > +static int arm64_hibernate_pm_notify(struct notifier_block *nb, > + unsigned long mode, void *unused) > +{ > + switch (mode) { > + default: > + break; > + case PM_POST_HIBERNATION: > + remap_linear_data_alias(true); > + break; > + case PM_HIBERNATION_PREPARE: > + remap_linear_data_alias(false); > + break; > + } > + return 0; > +} > + > void __init mark_linear_text_alias_ro(void) > { > /* > @@ -1064,6 +1088,16 @@ 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); > + > + remap_linear_data_alias(true); As suggested on v4, something like mark_linear_data_alias_valid(false) would be clearer. Also, is there anything stopping us from doing that directly in map_mem()? - Kevin > + > + if (IS_ENABLED(CONFIG_HIBERNATION)) { > + static struct notifier_block nb = { > + .notifier_call = arm64_hibernate_pm_notify > + }; > + > + register_pm_notifier(&nb); > + } > } > > #ifdef CONFIG_KFENCE > @@ -1189,11 +1223,6 @@ static void __init map_mem(void) > __map_memblock(start, end, pgprot_tagged(PAGE_KERNEL), > 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)); > } > > void mark_rodata_ro(void)