On 26/05/2026 19:59, 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. > > 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 <[email protected]> > --- > 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 <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 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)
