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181 lines
5.5 KiB
181 lines
5.5 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* This file implements KASLR memory randomization for x86_64. It randomizes |
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* the virtual address space of kernel memory regions (physical memory |
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* mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates |
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* exploits relying on predictable kernel addresses. |
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* |
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* Entropy is generated using the KASLR early boot functions now shared in |
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* the lib directory (originally written by Kees Cook). Randomization is |
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* done on PGD & P4D/PUD page table levels to increase possible addresses. |
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* The physical memory mapping code was adapted to support P4D/PUD level |
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* virtual addresses. This implementation on the best configuration provides |
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* 30,000 possible virtual addresses in average for each memory region. |
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* An additional low memory page is used to ensure each CPU can start with |
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* a PGD aligned virtual address (for realmode). |
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* |
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* The order of each memory region is not changed. The feature looks at |
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* the available space for the regions based on different configuration |
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* options and randomizes the base and space between each. The size of the |
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* physical memory mapping is the available physical memory. |
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*/ |
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#include <linux/kernel.h> |
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#include <linux/init.h> |
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#include <linux/random.h> |
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#include <linux/memblock.h> |
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#include <linux/pgtable.h> |
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#include <asm/setup.h> |
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#include <asm/kaslr.h> |
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#include "mm_internal.h" |
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#define TB_SHIFT 40 |
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/* |
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* The end address could depend on more configuration options to make the |
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* highest amount of space for randomization available, but that's too hard |
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* to keep straight and caused issues already. |
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*/ |
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static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE; |
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/* |
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* Memory regions randomized by KASLR (except modules that use a separate logic |
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* earlier during boot). The list is ordered based on virtual addresses. This |
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* order is kept after randomization. |
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*/ |
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static __initdata struct kaslr_memory_region { |
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unsigned long *base; |
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unsigned long size_tb; |
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} kaslr_regions[] = { |
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{ &page_offset_base, 0 }, |
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{ &vmalloc_base, 0 }, |
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{ &vmemmap_base, 0 }, |
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}; |
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/* Get size in bytes used by the memory region */ |
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static inline unsigned long get_padding(struct kaslr_memory_region *region) |
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{ |
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return (region->size_tb << TB_SHIFT); |
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} |
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/* Initialize base and padding for each memory region randomized with KASLR */ |
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void __init kernel_randomize_memory(void) |
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{ |
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size_t i; |
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unsigned long vaddr_start, vaddr; |
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unsigned long rand, memory_tb; |
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struct rnd_state rand_state; |
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unsigned long remain_entropy; |
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unsigned long vmemmap_size; |
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vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4; |
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vaddr = vaddr_start; |
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/* |
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* These BUILD_BUG_ON checks ensure the memory layout is consistent |
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* with the vaddr_start/vaddr_end variables. These checks are very |
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* limited.... |
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*/ |
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BUILD_BUG_ON(vaddr_start >= vaddr_end); |
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BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE); |
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BUILD_BUG_ON(vaddr_end > __START_KERNEL_map); |
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if (!kaslr_memory_enabled()) |
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return; |
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kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT); |
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kaslr_regions[1].size_tb = VMALLOC_SIZE_TB; |
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/* |
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* Update Physical memory mapping to available and |
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* add padding if needed (especially for memory hotplug support). |
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*/ |
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BUG_ON(kaslr_regions[0].base != &page_offset_base); |
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memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) + |
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CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING; |
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/* Adapt phyiscal memory region size based on available memory */ |
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if (memory_tb < kaslr_regions[0].size_tb) |
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kaslr_regions[0].size_tb = memory_tb; |
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/* |
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* Calculate the vmemmap region size in TBs, aligned to a TB |
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* boundary. |
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*/ |
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vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) * |
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sizeof(struct page); |
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kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT); |
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/* Calculate entropy available between regions */ |
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remain_entropy = vaddr_end - vaddr_start; |
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for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) |
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remain_entropy -= get_padding(&kaslr_regions[i]); |
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prandom_seed_state(&rand_state, kaslr_get_random_long("Memory")); |
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for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) { |
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unsigned long entropy; |
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/* |
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* Select a random virtual address using the extra entropy |
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* available. |
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*/ |
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entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i); |
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prandom_bytes_state(&rand_state, &rand, sizeof(rand)); |
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entropy = (rand % (entropy + 1)) & PUD_MASK; |
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vaddr += entropy; |
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*kaslr_regions[i].base = vaddr; |
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/* |
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* Jump the region and add a minimum padding based on |
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* randomization alignment. |
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*/ |
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vaddr += get_padding(&kaslr_regions[i]); |
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vaddr = round_up(vaddr + 1, PUD_SIZE); |
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remain_entropy -= entropy; |
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} |
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} |
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void __meminit init_trampoline_kaslr(void) |
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{ |
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pud_t *pud_page_tramp, *pud, *pud_tramp; |
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p4d_t *p4d_page_tramp, *p4d, *p4d_tramp; |
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unsigned long paddr, vaddr; |
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pgd_t *pgd; |
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pud_page_tramp = alloc_low_page(); |
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/* |
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* There are two mappings for the low 1MB area, the direct mapping |
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* and the 1:1 mapping for the real mode trampoline: |
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* |
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* Direct mapping: virt_addr = phys_addr + PAGE_OFFSET |
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* 1:1 mapping: virt_addr = phys_addr |
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*/ |
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paddr = 0; |
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vaddr = (unsigned long)__va(paddr); |
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pgd = pgd_offset_k(vaddr); |
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p4d = p4d_offset(pgd, vaddr); |
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pud = pud_offset(p4d, vaddr); |
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pud_tramp = pud_page_tramp + pud_index(paddr); |
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*pud_tramp = *pud; |
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if (pgtable_l5_enabled()) { |
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p4d_page_tramp = alloc_low_page(); |
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p4d_tramp = p4d_page_tramp + p4d_index(paddr); |
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set_p4d(p4d_tramp, |
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__p4d(_KERNPG_TABLE | __pa(pud_page_tramp))); |
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set_pgd(&trampoline_pgd_entry, |
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__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp))); |
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} else { |
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set_pgd(&trampoline_pgd_entry, |
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__pgd(_KERNPG_TABLE | __pa(pud_page_tramp))); |
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} |
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}
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