[thirdparty/kernel/linux.git] / arch / x86 / mm / kaslr.c

// SPDX-License-Identifier: GPL-2.0
/*
 * This file implements KASLR memory randomization for x86_64. It randomizes
 * the virtual address space of kernel memory regions (physical memory
 * mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates
 * exploits relying on predictable kernel addresses.
 *
 * Entropy is generated using the KASLR early boot functions now shared in
 * the lib directory (originally written by Kees Cook). Randomization is
 * done on PGD & P4D/PUD page table levels to increase possible addresses.
 * The physical memory mapping code was adapted to support P4D/PUD level
 * virtual addresses. This implementation on the best configuration provides
 * 30,000 possible virtual addresses in average for each memory region.
 * An additional low memory page is used to ensure each CPU can start with
 * a PGD aligned virtual address (for realmode).
 *
 * The order of each memory region is not changed. The feature looks at
 * the available space for the regions based on different configuration
 * options and randomizes the base and space between each. The size of the
 * physical memory mapping is the available physical memory.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/random.h>

#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/setup.h>
#include <asm/kaslr.h>

#include "mm_internal.h"

#define TB_SHIFT 40

/*
 * Virtual address start and end range for randomization. The end changes base
 * on configuration to have the highest amount of space for randomization.
 * It increases the possible random position for each randomized region.
 *
 * You need to add an if/def entry if you introduce a new memory region
 * compatible with KASLR. Your entry must be in logical order with memory
 * layout. For example, ESPFIX is before EFI because its virtual address is
 * before. You also need to add a BUILD_BUG_ON() in kernel_randomize_memory() to
 * ensure that this order is correct and won't be changed.
 */
static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;

#if defined(CONFIG_X86_ESPFIX64)
static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
#elif defined(CONFIG_EFI)
static const unsigned long vaddr_end = EFI_VA_END;
#else
static const unsigned long vaddr_end = __START_KERNEL_map;
#endif

/* Default values */
unsigned long page_offset_base = __PAGE_OFFSET_BASE;
EXPORT_SYMBOL(page_offset_base);
unsigned long vmalloc_base = __VMALLOC_BASE;
EXPORT_SYMBOL(vmalloc_base);
unsigned long vmemmap_base = __VMEMMAP_BASE;
EXPORT_SYMBOL(vmemmap_base);

/*
 * Memory regions randomized by KASLR (except modules that use a separate logic
 * earlier during boot). The list is ordered based on virtual addresses. This
 * order is kept after randomization.
 */
static __initdata struct kaslr_memory_region {
	unsigned long *base;
	unsigned long size_tb;
} kaslr_regions[] = {
	{ &page_offset_base, 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT) /* Maximum */ },
	{ &vmalloc_base, VMALLOC_SIZE_TB },
	{ &vmemmap_base, 1 },
};

/* Get size in bytes used by the memory region */
static inline unsigned long get_padding(struct kaslr_memory_region *region)
{
	return (region->size_tb << TB_SHIFT);
}

/*
 * Apply no randomization if KASLR was disabled at boot or if KASAN
 * is enabled. KASAN shadow mappings rely on regions being PGD aligned.
 */
static inline bool kaslr_memory_enabled(void)
{
	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}

/* Initialize base and padding for each memory region randomized with KASLR */
void __init kernel_randomize_memory(void)
{
	size_t i;
	unsigned long vaddr = vaddr_start;
	unsigned long rand, memory_tb;
	struct rnd_state rand_state;
	unsigned long remain_entropy;

	/*
	 * All these BUILD_BUG_ON checks ensures the memory layout is
	 * consistent with the vaddr_start/vaddr_end variables.
	 */
	BUILD_BUG_ON(vaddr_start >= vaddr_end);
	BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_ESPFIX64) &&
		     vaddr_end >= EFI_VA_END);
	BUILD_BUG_ON((IS_ENABLED(CONFIG_X86_ESPFIX64) ||
		      IS_ENABLED(CONFIG_EFI)) &&
		     vaddr_end >= __START_KERNEL_map);
	BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);

	if (!kaslr_memory_enabled())
		return;

	/*
	 * Update Physical memory mapping to available and
	 * add padding if needed (especially for memory hotplug support).
	 */
	BUG_ON(kaslr_regions[0].base != &page_offset_base);
	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;

	/* Adapt phyiscal memory region size based on available memory */
	if (memory_tb < kaslr_regions[0].size_tb)
		kaslr_regions[0].size_tb = memory_tb;

	/* Calculate entropy available between regions */
	remain_entropy = vaddr_end - vaddr_start;
	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
		remain_entropy -= get_padding(&kaslr_regions[i]);

	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));

	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
		unsigned long entropy;

		/*
		 * Select a random virtual address using the extra entropy
		 * available.
		 */
		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
		prandom_bytes_state(&rand_state, &rand, sizeof(rand));
		if (IS_ENABLED(CONFIG_X86_5LEVEL))
			entropy = (rand % (entropy + 1)) & P4D_MASK;
		else
			entropy = (rand % (entropy + 1)) & PUD_MASK;
		vaddr += entropy;
		*kaslr_regions[i].base = vaddr;

		/*
		 * Jump the region and add a minimum padding based on
		 * randomization alignment.
		 */
		vaddr += get_padding(&kaslr_regions[i]);
		if (IS_ENABLED(CONFIG_X86_5LEVEL))
			vaddr = round_up(vaddr + 1, P4D_SIZE);
		else
			vaddr = round_up(vaddr + 1, PUD_SIZE);
		remain_entropy -= entropy;
	}
}

static void __meminit init_trampoline_pud(void)
{
	unsigned long paddr, paddr_next;
	pgd_t *pgd;
	pud_t *pud_page, *pud_page_tramp;
	int i;

	pud_page_tramp = alloc_low_page();

	paddr = 0;
	pgd = pgd_offset_k((unsigned long)__va(paddr));
	pud_page = (pud_t *) pgd_page_vaddr(*pgd);

	for (i = pud_index(paddr); i < PTRS_PER_PUD; i++, paddr = paddr_next) {
		pud_t *pud, *pud_tramp;
		unsigned long vaddr = (unsigned long)__va(paddr);

		pud_tramp = pud_page_tramp + pud_index(paddr);
		pud = pud_page + pud_index(vaddr);
		paddr_next = (paddr & PUD_MASK) + PUD_SIZE;

		*pud_tramp = *pud;
	}

	set_pgd(&trampoline_pgd_entry,
		__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
}

static void __meminit init_trampoline_p4d(void)
{
	unsigned long paddr, paddr_next;
	pgd_t *pgd;
	p4d_t *p4d_page, *p4d_page_tramp;
	int i;

	p4d_page_tramp = alloc_low_page();

	paddr = 0;
	pgd = pgd_offset_k((unsigned long)__va(paddr));
	p4d_page = (p4d_t *) pgd_page_vaddr(*pgd);

	for (i = p4d_index(paddr); i < PTRS_PER_P4D; i++, paddr = paddr_next) {
		p4d_t *p4d, *p4d_tramp;
		unsigned long vaddr = (unsigned long)__va(paddr);

		p4d_tramp = p4d_page_tramp + p4d_index(paddr);
		p4d = p4d_page + p4d_index(vaddr);
		paddr_next = (paddr & P4D_MASK) + P4D_SIZE;

		*p4d_tramp = *p4d;
	}

	set_pgd(&trampoline_pgd_entry,
		__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
}

/*
 * Create PGD aligned trampoline table to allow real mode initialization
 * of additional CPUs. Consume only 1 low memory page.
 */
void __meminit init_trampoline(void)
{

	if (!kaslr_memory_enabled()) {
		init_trampoline_default();
		return;
	}

	if (IS_ENABLED(CONFIG_X86_5LEVEL))
		init_trampoline_p4d();
	else
		init_trampoline_pud();
}
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
0483e1fa TG	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
8624c1f6 KS	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).
0483e1fa TG	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
	27	#include <asm/pgalloc.h>
	28	#include <asm/pgtable.h>
	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	* Virtual address start and end range for randomization. The end changes base
	38	* on configuration to have the highest amount of space for randomization.
	39	* It increases the possible random position for each randomized region.
	40	*
	41	* You need to add an if/def entry if you introduce a new memory region
	42	* compatible with KASLR. Your entry must be in logical order with memory
	43	* layout. For example, ESPFIX is before EFI because its virtual address is
25dfe478	44	* before. You also need to add a BUILD_BUG_ON() in kernel_randomize_memory() to
0483e1fa TG	45	* ensure that this order is correct and won't be changed.
0483e1fa TG	46	*/
021182e5	47	static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
25dfe478 TG	48
	49	#if defined(CONFIG_X86_ESPFIX64)
	50	static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
	51	#elif defined(CONFIG_EFI)
a46f60d7	52	static const unsigned long vaddr_end = EFI_VA_END;
25dfe478 TG	53	#else
	54	static const unsigned long vaddr_end = __START_KERNEL_map;
	55	#endif
021182e5 TG	56
	57	/* Default values */
	58	unsigned long page_offset_base = __PAGE_OFFSET_BASE;
	59	EXPORT_SYMBOL(page_offset_base);
a95ae27c TG	60	unsigned long vmalloc_base = __VMALLOC_BASE;
a95ae27c TG	61	EXPORT_SYMBOL(vmalloc_base);
25dfe478 TG	62	unsigned long vmemmap_base = __VMEMMAP_BASE;
25dfe478 TG	63	EXPORT_SYMBOL(vmemmap_base);
0483e1fa TG	64
	65	/*
	66	* Memory regions randomized by KASLR (except modules that use a separate logic
	67	* earlier during boot). The list is ordered based on virtual addresses. This
	68	* order is kept after randomization.
	69	*/
	70	static __initdata struct kaslr_memory_region {
	71	unsigned long *base;
	72	unsigned long size_tb;
	73	} kaslr_regions[] = {
8624c1f6	74	{ &page_offset_base, 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT) /* Maximum */ },
a95ae27c	75	{ &vmalloc_base, VMALLOC_SIZE_TB },
25dfe478	76	{ &vmemmap_base, 1 },
0483e1fa TG	77	};
	78
	79	/* Get size in bytes used by the memory region */
	80	static inline unsigned long get_padding(struct kaslr_memory_region *region)
	81	{
	82	return (region->size_tb << TB_SHIFT);
	83	}
	84
	85	/*
	86	* Apply no randomization if KASLR was disabled at boot or if KASAN
	87	* is enabled. KASAN shadow mappings rely on regions being PGD aligned.
	88	*/
	89	static inline bool kaslr_memory_enabled(void)
	90	{
a5ff1b34	91	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
0483e1fa TG	92	}
	93
	94	/* Initialize base and padding for each memory region randomized with KASLR */
	95	void __init kernel_randomize_memory(void)
	96	{
	97	size_t i;
	98	unsigned long vaddr = vaddr_start;
021182e5	99	unsigned long rand, memory_tb;
0483e1fa TG	100	struct rnd_state rand_state;
	101	unsigned long remain_entropy;
	102
25dfe478 TG	103	/*
	104	* All these BUILD_BUG_ON checks ensures the memory layout is
	105	* consistent with the vaddr_start/vaddr_end variables.
	106	*/
	107	BUILD_BUG_ON(vaddr_start >= vaddr_end);
c0a0aba8	108	BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_ESPFIX64) &&
a46f60d7	109	vaddr_end >= EFI_VA_END);
c0a0aba8 MY	110	BUILD_BUG_ON((IS_ENABLED(CONFIG_X86_ESPFIX64) \|\|
c0a0aba8 MY	111	IS_ENABLED(CONFIG_EFI)) &&
25dfe478 TG	112	vaddr_end >= __START_KERNEL_map);
	113	BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
	114
0483e1fa TG	115	if (!kaslr_memory_enabled())
	116	return;
	117
90397a41 TG	118	/*
	119	* Update Physical memory mapping to available and
	120	* add padding if needed (especially for memory hotplug support).
	121	*/
021182e5	122	BUG_ON(kaslr_regions[0].base != &page_offset_base);
c7d2361f	123	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
90397a41	124	CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
021182e5 TG	125
	126	/* Adapt phyiscal memory region size based on available memory */
	127	if (memory_tb < kaslr_regions[0].size_tb)
	128	kaslr_regions[0].size_tb = memory_tb;
	129
0483e1fa TG	130	/* Calculate entropy available between regions */
	131	remain_entropy = vaddr_end - vaddr_start;
	132	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
	133	remain_entropy -= get_padding(&kaslr_regions[i]);
	134
	135	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
	136
	137	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
	138	unsigned long entropy;
	139
	140	/*
	141	* Select a random virtual address using the extra entropy
	142	* available.
	143	*/
	144	entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
	145	prandom_bytes_state(&rand_state, &rand, sizeof(rand));
8624c1f6 KS	146	if (IS_ENABLED(CONFIG_X86_5LEVEL))
	147	entropy = (rand % (entropy + 1)) & P4D_MASK;
	148	else
	149	entropy = (rand % (entropy + 1)) & PUD_MASK;
0483e1fa TG	150	vaddr += entropy;
	151	*kaslr_regions[i].base = vaddr;
	152
	153	/*
	154	* Jump the region and add a minimum padding based on
	155	* randomization alignment.
	156	*/
	157	vaddr += get_padding(&kaslr_regions[i]);
8624c1f6 KS	158	if (IS_ENABLED(CONFIG_X86_5LEVEL))
	159	vaddr = round_up(vaddr + 1, P4D_SIZE);
	160	else
	161	vaddr = round_up(vaddr + 1, PUD_SIZE);
0483e1fa TG	162	remain_entropy -= entropy;
	163	}
	164	}
	165
8624c1f6	166	static void __meminit init_trampoline_pud(void)
0483e1fa TG	167	{
	168	unsigned long paddr, paddr_next;
	169	pgd_t *pgd;
	170	pud_t pud_page, pud_page_tramp;
	171	int i;
	172
0483e1fa TG	173	pud_page_tramp = alloc_low_page();
	174
	175	paddr = 0;
	176	pgd = pgd_offset_k((unsigned long)__va(paddr));
	177	pud_page = (pud_t ) pgd_page_vaddr(pgd);
	178
	179	for (i = pud_index(paddr); i < PTRS_PER_PUD; i++, paddr = paddr_next) {
	180	pud_t pud, pud_tramp;
	181	unsigned long vaddr = (unsigned long)__va(paddr);
	182
	183	pud_tramp = pud_page_tramp + pud_index(paddr);
	184	pud = pud_page + pud_index(vaddr);
	185	paddr_next = (paddr & PUD_MASK) + PUD_SIZE;
	186
	187	pud_tramp = pud;
	188	}
	189
	190	set_pgd(&trampoline_pgd_entry,
	191	__pgd(_KERNPG_TABLE \| __pa(pud_page_tramp)));
	192	}
8624c1f6 KS	193
	194	static void __meminit init_trampoline_p4d(void)
	195	{
	196	unsigned long paddr, paddr_next;
	197	pgd_t *pgd;
	198	p4d_t p4d_page, p4d_page_tramp;
	199	int i;
	200
	201	p4d_page_tramp = alloc_low_page();
	202
	203	paddr = 0;
	204	pgd = pgd_offset_k((unsigned long)__va(paddr));
	205	p4d_page = (p4d_t ) pgd_page_vaddr(pgd);
	206
	207	for (i = p4d_index(paddr); i < PTRS_PER_P4D; i++, paddr = paddr_next) {
	208	p4d_t p4d, p4d_tramp;
	209	unsigned long vaddr = (unsigned long)__va(paddr);
	210
	211	p4d_tramp = p4d_page_tramp + p4d_index(paddr);
	212	p4d = p4d_page + p4d_index(vaddr);
	213	paddr_next = (paddr & P4D_MASK) + P4D_SIZE;
	214
	215	p4d_tramp = p4d;
	216	}
	217
	218	set_pgd(&trampoline_pgd_entry,
	219	__pgd(_KERNPG_TABLE \| __pa(p4d_page_tramp)));
	220	}
	221
	222	/*
	223	* Create PGD aligned trampoline table to allow real mode initialization
	224	* of additional CPUs. Consume only 1 low memory page.
	225	*/
	226	void __meminit init_trampoline(void)
	227	{
	228
	229	if (!kaslr_memory_enabled()) {
	230	init_trampoline_default();
	231	return;
	232	}
	233
	234	if (IS_ENABLED(CONFIG_X86_5LEVEL))
	235	init_trampoline_p4d();
	236	else
	237	init_trampoline_pud();
	238	}