1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * This file implements KASLR memory randomization for x86_64. It randomizes
  4 * the virtual address space of kernel memory regions (physical memory
  5 * mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates
  6 * exploits relying on predictable kernel addresses.
  7 *
  8 * Entropy is generated using the KASLR early boot functions now shared in
  9 * the lib directory (originally written by Kees Cook). Randomization is
 10 * done on PGD & P4D/PUD page table levels to increase possible addresses.
 11 * The physical memory mapping code was adapted to support P4D/PUD level
 12 * virtual addresses. This implementation on the best configuration provides
 13 * 30,000 possible virtual addresses in average for each memory region.
 14 * An additional low memory page is used to ensure each CPU can start with
 15 * a PGD aligned virtual address (for realmode).
 16 *
 17 * The order of each memory region is not changed. The feature looks at
 18 * the available space for the regions based on different configuration
 19 * options and randomizes the base and space between each. The size of the
 20 * physical memory mapping is the available physical memory.
 21 */
 22
 23#include <linux/kernel.h>
 24#include <linux/init.h>
 25#include <linux/random.h>
 26#include <linux/memblock.h>
 27#include <linux/pgtable.h>
 28
 
 
 29#include <asm/setup.h>
 30#include <asm/kaslr.h>
 31
 32#include "mm_internal.h"
 33
 34#define TB_SHIFT 40
 35
 36/*
 37 * The end address could depend on more configuration options to make the
 38 * highest amount of space for randomization available, but that's too hard
 39 * to keep straight and caused issues already.
 40 */
 41static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;
 42
 43/*
 44 * Memory regions randomized by KASLR (except modules that use a separate logic
 45 * earlier during boot). The list is ordered based on virtual addresses. This
 46 * order is kept after randomization.
 47 */
 48static __initdata struct kaslr_memory_region {
 49	unsigned long *base;
 50	unsigned long size_tb;
 51} kaslr_regions[] = {
 52	{ &page_offset_base, 0 },
 53	{ &vmalloc_base, 0 },
 54	{ &vmemmap_base, 0 },
 55};
 56
 57/* Get size in bytes used by the memory region */
 58static inline unsigned long get_padding(struct kaslr_memory_region *region)
 59{
 60	return (region->size_tb << TB_SHIFT);
 61}
 62
 
 
 
 
 
 
 
 
 
 63/* Initialize base and padding for each memory region randomized with KASLR */
 64void __init kernel_randomize_memory(void)
 65{
 66	size_t i;
 67	unsigned long vaddr_start, vaddr;
 68	unsigned long rand, memory_tb;
 69	struct rnd_state rand_state;
 70	unsigned long remain_entropy;
 71	unsigned long vmemmap_size;
 72
 73	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
 74	vaddr = vaddr_start;
 75
 76	/*
 77	 * These BUILD_BUG_ON checks ensure the memory layout is consistent
 78	 * with the vaddr_start/vaddr_end variables. These checks are very
 79	 * limited....
 80	 */
 81	BUILD_BUG_ON(vaddr_start >= vaddr_end);
 82	BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE);
 83	BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
 84
 85	if (!kaslr_memory_enabled())
 86		return;
 87
 88	kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
 89	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
 90
 91	/*
 92	 * Update Physical memory mapping to available and
 93	 * add padding if needed (especially for memory hotplug support).
 94	 */
 95	BUG_ON(kaslr_regions[0].base != &page_offset_base);
 96	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
 97		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
 98
 99	/* Adapt physical memory region size based on available memory */
100	if (memory_tb < kaslr_regions[0].size_tb)
101		kaslr_regions[0].size_tb = memory_tb;
102
103	/*
104	 * Calculate the vmemmap region size in TBs, aligned to a TB
105	 * boundary.
106	 */
107	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
108			sizeof(struct page);
109	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
110
111	/* Calculate entropy available between regions */
112	remain_entropy = vaddr_end - vaddr_start;
113	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
114		remain_entropy -= get_padding(&kaslr_regions[i]);
115
116	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
117
118	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
119		unsigned long entropy;
120
121		/*
122		 * Select a random virtual address using the extra entropy
123		 * available.
124		 */
125		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
126		prandom_bytes_state(&rand_state, &rand, sizeof(rand));
127		entropy = (rand % (entropy + 1)) & PUD_MASK;
128		vaddr += entropy;
129		*kaslr_regions[i].base = vaddr;
130
131		/*
132		 * Jump the region and add a minimum padding based on
133		 * randomization alignment.
134		 */
135		vaddr += get_padding(&kaslr_regions[i]);
136		vaddr = round_up(vaddr + 1, PUD_SIZE);
137		remain_entropy -= entropy;
138	}
139}
140
141void __meminit init_trampoline_kaslr(void)
142{
143	pud_t *pud_page_tramp, *pud, *pud_tramp;
144	p4d_t *p4d_page_tramp, *p4d, *p4d_tramp;
145	unsigned long paddr, vaddr;
146	pgd_t *pgd;
147
148	pud_page_tramp = alloc_low_page();
149
150	/*
151	 * There are two mappings for the low 1MB area, the direct mapping
152	 * and the 1:1 mapping for the real mode trampoline:
153	 *
154	 * Direct mapping: virt_addr = phys_addr + PAGE_OFFSET
155	 * 1:1 mapping:    virt_addr = phys_addr
156	 */
157	paddr = 0;
158	vaddr = (unsigned long)__va(paddr);
159	pgd = pgd_offset_k(vaddr);
160
161	p4d = p4d_offset(pgd, vaddr);
162	pud = pud_offset(p4d, vaddr);
163
164	pud_tramp = pud_page_tramp + pud_index(paddr);
165	*pud_tramp = *pud;
166
167	if (pgtable_l5_enabled()) {
168		p4d_page_tramp = alloc_low_page();
169
170		p4d_tramp = p4d_page_tramp + p4d_index(paddr);
171
172		set_p4d(p4d_tramp,
173			__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
174
175		set_pgd(&trampoline_pgd_entry,
176			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
177	} else {
178		set_pgd(&trampoline_pgd_entry,
179			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
180	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
181}

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * This file implements KASLR memory randomization for x86_64. It randomizes
  4 * the virtual address space of kernel memory regions (physical memory
  5 * mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates
  6 * exploits relying on predictable kernel addresses.
  7 *
  8 * Entropy is generated using the KASLR early boot functions now shared in
  9 * the lib directory (originally written by Kees Cook). Randomization is
 10 * done on PGD & P4D/PUD page table levels to increase possible addresses.
 11 * The physical memory mapping code was adapted to support P4D/PUD level
 12 * virtual addresses. This implementation on the best configuration provides
 13 * 30,000 possible virtual addresses in average for each memory region.
 14 * An additional low memory page is used to ensure each CPU can start with
 15 * a PGD aligned virtual address (for realmode).
 16 *
 17 * The order of each memory region is not changed. The feature looks at
 18 * the available space for the regions based on different configuration
 19 * options and randomizes the base and space between each. The size of the
 20 * physical memory mapping is the available physical memory.
 21 */
 22
 23#include <linux/kernel.h>
 24#include <linux/init.h>
 25#include <linux/random.h>
 26#include <linux/memblock.h>
 
 27
 28#include <asm/pgalloc.h>
 29#include <asm/pgtable.h>
 30#include <asm/setup.h>
 31#include <asm/kaslr.h>
 32
 33#include "mm_internal.h"
 34
 35#define TB_SHIFT 40
 36
 37/*
 38 * The end address could depend on more configuration options to make the
 39 * highest amount of space for randomization available, but that's too hard
 40 * to keep straight and caused issues already.
 41 */
 42static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;
 43
 44/*
 45 * Memory regions randomized by KASLR (except modules that use a separate logic
 46 * earlier during boot). The list is ordered based on virtual addresses. This
 47 * order is kept after randomization.
 48 */
 49static __initdata struct kaslr_memory_region {
 50	unsigned long *base;
 51	unsigned long size_tb;
 52} kaslr_regions[] = {
 53	{ &page_offset_base, 0 },
 54	{ &vmalloc_base, 0 },
 55	{ &vmemmap_base, 0 },
 56};
 57
 58/* Get size in bytes used by the memory region */
 59static inline unsigned long get_padding(struct kaslr_memory_region *region)
 60{
 61	return (region->size_tb << TB_SHIFT);
 62}
 63
 64/*
 65 * Apply no randomization if KASLR was disabled at boot or if KASAN
 66 * is enabled. KASAN shadow mappings rely on regions being PGD aligned.
 67 */
 68static inline bool kaslr_memory_enabled(void)
 69{
 70	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
 71}
 72
 73/* Initialize base and padding for each memory region randomized with KASLR */
 74void __init kernel_randomize_memory(void)
 75{
 76	size_t i;
 77	unsigned long vaddr_start, vaddr;
 78	unsigned long rand, memory_tb;
 79	struct rnd_state rand_state;
 80	unsigned long remain_entropy;
 81	unsigned long vmemmap_size;
 82
 83	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
 84	vaddr = vaddr_start;
 85
 86	/*
 87	 * These BUILD_BUG_ON checks ensure the memory layout is consistent
 88	 * with the vaddr_start/vaddr_end variables. These checks are very
 89	 * limited....
 90	 */
 91	BUILD_BUG_ON(vaddr_start >= vaddr_end);
 92	BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE);
 93	BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
 94
 95	if (!kaslr_memory_enabled())
 96		return;
 97
 98	kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
 99	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
100
101	/*
102	 * Update Physical memory mapping to available and
103	 * add padding if needed (especially for memory hotplug support).
104	 */
105	BUG_ON(kaslr_regions[0].base != &page_offset_base);
106	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
107		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
108
109	/* Adapt phyiscal memory region size based on available memory */
110	if (memory_tb < kaslr_regions[0].size_tb)
111		kaslr_regions[0].size_tb = memory_tb;
112
113	/*
114	 * Calculate the vmemmap region size in TBs, aligned to a TB
115	 * boundary.
116	 */
117	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
118			sizeof(struct page);
119	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
120
121	/* Calculate entropy available between regions */
122	remain_entropy = vaddr_end - vaddr_start;
123	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
124		remain_entropy -= get_padding(&kaslr_regions[i]);
125
126	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
127
128	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
129		unsigned long entropy;
130
131		/*
132		 * Select a random virtual address using the extra entropy
133		 * available.
134		 */
135		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
136		prandom_bytes_state(&rand_state, &rand, sizeof(rand));
137		entropy = (rand % (entropy + 1)) & PUD_MASK;
138		vaddr += entropy;
139		*kaslr_regions[i].base = vaddr;
140
141		/*
142		 * Jump the region and add a minimum padding based on
143		 * randomization alignment.
144		 */
145		vaddr += get_padding(&kaslr_regions[i]);
146		vaddr = round_up(vaddr + 1, PUD_SIZE);
147		remain_entropy -= entropy;
148	}
149}
150
151static void __meminit init_trampoline_pud(void)
152{
153	pud_t *pud_page_tramp, *pud, *pud_tramp;
154	p4d_t *p4d_page_tramp, *p4d, *p4d_tramp;
155	unsigned long paddr, vaddr;
156	pgd_t *pgd;
157
158	pud_page_tramp = alloc_low_page();
159
160	/*
161	 * There are two mappings for the low 1MB area, the direct mapping
162	 * and the 1:1 mapping for the real mode trampoline:
163	 *
164	 * Direct mapping: virt_addr = phys_addr + PAGE_OFFSET
165	 * 1:1 mapping:    virt_addr = phys_addr
166	 */
167	paddr = 0;
168	vaddr = (unsigned long)__va(paddr);
169	pgd = pgd_offset_k(vaddr);
170
171	p4d = p4d_offset(pgd, vaddr);
172	pud = pud_offset(p4d, vaddr);
173
174	pud_tramp = pud_page_tramp + pud_index(paddr);
175	*pud_tramp = *pud;
176
177	if (pgtable_l5_enabled()) {
178		p4d_page_tramp = alloc_low_page();
179
180		p4d_tramp = p4d_page_tramp + p4d_index(paddr);
181
182		set_p4d(p4d_tramp,
183			__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
184
185		set_pgd(&trampoline_pgd_entry,
186			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
187	} else {
188		set_pgd(&trampoline_pgd_entry,
189			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
190	}
191}
192
193/*
194 * The real mode trampoline, which is required for bootstrapping CPUs
195 * occupies only a small area under the low 1MB.  See reserve_real_mode()
196 * for details.
197 *
198 * If KASLR is disabled the first PGD entry of the direct mapping is copied
199 * to map the real mode trampoline.
200 *
201 * If KASLR is enabled, copy only the PUD which covers the low 1MB
202 * area. This limits the randomization granularity to 1GB for both 4-level
203 * and 5-level paging.
204 */
205void __meminit init_trampoline(void)
206{
207	if (!kaslr_memory_enabled()) {
208		init_trampoline_default();
209		return;
210	}
211
212	init_trampoline_pud();
213}