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arm64: mm: Unmap kernel data/bss entirely from the linear map

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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.

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.

Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Liz Prucka <lizprucka@google.com>
Cc: Seth Jenkins <sethjenkins@google.com>
Cc: Kees Cook <kees@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ard Biesheuvel 2026-08-03 18:33:47 +02:00 committed by Will Deacon
parent 7ace06a01e
commit fb0f3ef560
1 changed files with 41 additions and 5 deletions
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46
arch/arm64/mm/mmu.c
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@ -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>
@ -1062,6 +1063,29 @@ 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)
{
/*
@ -1070,6 +1094,21 @@ 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/write 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) && rodata_enabled) {
static struct notifier_block nb = {
.notifier_call = arm64_hibernate_pm_notify
};
register_pm_notifier(&nb);
}
}
#ifdef CONFIG_KFENCE
@ -1231,11 +1270,8 @@ void mark_rodata_ro(void)
(unsigned long)_stext - (unsigned long)_text,
PAGE_KERNEL_RO);
/* Map the kernel data/bss read-only in the linear map */
update_mapping_prot(__pa_symbol(__init_end),
(unsigned long)lm_alias(__init_end),
(unsigned long)__bss_stop - (unsigned long)__init_end,
PAGE_KERNEL_RO);
/* Map the kernel data/bss as invalid in the linear map */
mark_linear_data_alias_valid(false);
}
static void __init declare_vma(struct vm_struct *vma,