From: Kevin Brodsky <kevin.brodsky@arm•com>
To: Ard Biesheuvel <ardb+git@google•com>,
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 <ardb@kernel•org>,
Ryan Roberts <ryan.roberts@arm•com>,
Anshuman Khandual <anshuman.khandual@arm•com>,
Liz Prucka <lizprucka@google•com>,
Seth Jenkins <sethjenkins@google•com>,
Kees Cook <kees@kernel•org>, Mike Rapoport <rppt@kernel•org>,
David Hildenbrand <david@kernel•org>,
Andrew Morton <akpm@linux-foundation•org>,
Jann Horn <jannh@google•com>,
linux-mm@kvack•org, linux-hardening@vger•kernel.org,
linuxppc-dev@lists•ozlabs.org, linux-sh@vger•kernel.org
Subject: Re: [PATCH v7 15/15] arm64: mm: Unmap kernel data/bss entirely from the linear map
Date: Mon, 1 Jun 2026 12:43:29 +0200 [thread overview]
Message-ID: <e9187fdb-b4dc-4b82-8783-fe1eb221d885@arm.com> (raw)
In-Reply-To: <20260529150150.1670604-32-ardb+git@google.com>
On 29/05/2026 17:02, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel•org>
>
> 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 <kevin.brodsky@arm•com>
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 <ardb@kernel•org>
> ---
> 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 <linux/mm.h>
> #include <linux/vmalloc.h>
> #include <linux/set_memory.h>
> +#include <linux/suspend.h>
> #include <linux/kfence.h>
> #include <linux/pkeys.h>
> #include <linux/mm_inline.h>
> @@ -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)
next prev parent reply other threads:[~2026-06-01 10:43 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-29 15:01 [PATCH v7 00/15] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 01/15] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 02/15] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 03/15] arm64: mm: Check for pud_/pmd_set_huge() failures on kernel mappings Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 04/15] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 05/15] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 06/15] arm64: mm: Permit contiguous descriptors to be manipulated Ard Biesheuvel
2026-05-29 15:01 ` [PATCH v7 07/15] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-06-01 10:42 ` Kevin Brodsky
2026-05-29 15:01 ` [PATCH v7 08/15] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-05-29 15:02 ` [PATCH v7 09/15] arm64: Move fixmap and kasan page tables to end of kernel image Ard Biesheuvel
2026-05-29 15:02 ` [PATCH v7 10/15] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-06-01 10:43 ` Kevin Brodsky
2026-05-29 15:02 ` [PATCH v7 11/15] powerpc/code-patching: Avoid r/w mapping of the zero page Ard Biesheuvel
2026-06-03 18:03 ` Mukesh Kumar Chaurasiya
2026-06-04 7:43 ` Christophe Leroy (CS GROUP)
2026-05-29 15:02 ` [PATCH v7 12/15] sh: Drop cache flush of the zero page at boot Ard Biesheuvel
2026-05-30 16:19 ` Mike Rapoport
2026-06-01 8:11 ` Geert Uytterhoeven
2026-05-29 15:02 ` [PATCH v7 13/15] mm: Make empty_zero_page[] const Ard Biesheuvel
2026-05-29 15:02 ` [PATCH v7 14/15] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-05-29 15:02 ` [PATCH v7 15/15] arm64: mm: Unmap kernel data/bss entirely from " Ard Biesheuvel
2026-06-01 10:43 ` Kevin Brodsky [this message]
2026-06-02 20:34 ` [PATCH v7 00/15] arm64: Unmap linear alias of kernel data/bss Will Deacon
2026-06-03 8:57 ` Ard Biesheuvel
2026-06-03 11:22 ` Will Deacon
2026-06-03 11:24 ` Ard Biesheuvel
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