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. 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); arm64_kfence_map_pool(early_kfence_pool); } -- 2.52.0.457.g6b5491de43-goog
