On 26/01/2026 09:26, Ard Biesheuvel wrote: > From: Ard Biesheuvel <[email protected]> > > 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.
what about ro_after_init? Could that contain secrets that we don't want to leak? What is the advantage of leaving text/rodata ro in the linear map vs just umapping the whole lot? > > 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. > > Signed-off-by: Ard Biesheuvel <[email protected]> > --- > arch/arm64/mm/mmu.c | 40 ++++++++++++++++++-- > 1 file changed, 37 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index fdbbb018adc5..06b2d11b4561 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> > @@ -1027,6 +1028,31 @@ 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)(__pgdir_start - __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: > + case PM_POST_RESTORE: > + remap_linear_data_alias(true); > + break; > + case PM_HIBERNATION_PREPARE: > + case PM_RESTORE_PREPARE: > + remap_linear_data_alias(false); > + break; > + } > + return 0; > +} > + > void __init mark_linear_text_alias_ro(void) > { > /* > @@ -1035,6 +1061,16 @@ 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); > + > + if (IS_ENABLED(CONFIG_HIBERNATION)) { > + static struct notifier_block nb = { > + .notifier_call = arm64_hibernate_pm_notify > + }; > + > + register_pm_notifier(&nb); > + } > } > > #ifdef CONFIG_KFENCE > @@ -1163,7 +1199,7 @@ static void __init map_mem(void) > __map_memblock(kernel_start, init_begin, PAGE_KERNEL, > flags | NO_CONT_MAPPINGS); > __map_memblock(init_end, kernel_end, PAGE_KERNEL, > - flags | NO_CONT_MAPPINGS); > + flags | NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS); > > /* map all the memory banks */ > for_each_mem_range(i, &start, &end) { > @@ -1176,8 +1212,6 @@ static void __init map_mem(void) > flags); > } > > - __map_memblock(init_end, kernel_end, PAGE_KERNEL_RO, > - flags | NO_CONT_MAPPINGS); In the previous patch, perhaps this should be moved to mark_linear_text_alias_ro() and combined with the update_mapping_prot() there? Thanks, Ryan > arm64_kfence_map_pool(early_kfence_pool); > } >
