[mirror_ubuntu-disco-kernel.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 address could depend on more configuration options to make the
 * highest amount of space for randomization available, but that's too hard
 * to keep straight and caused issues already.
 */
static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;

/* 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;

	/*
	 * These BUILD_BUG_ON checks ensure the memory layout is consistent
	 * with the vaddr_start/vaddr_end variables. These checks are very
	 * limited....
	 */
	BUILD_BUG_ON(vaddr_start >= vaddr_end);
	BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE);
	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	/*
1dddd251	37	* Virtual address start and end range for randomization.
0483e1fa	38	*
1dddd251 TG	39	* The end address could depend on more configuration options to make the
	40	* highest amount of space for randomization available, but that's too hard
	41	* to keep straight and caused issues already.
0483e1fa	42	*/
021182e5	43	static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
1dddd251	44	static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;
021182e5 TG	45
	46	/* Default values */
	47	unsigned long page_offset_base = __PAGE_OFFSET_BASE;
	48	EXPORT_SYMBOL(page_offset_base);
a95ae27c TG	49	unsigned long vmalloc_base = __VMALLOC_BASE;
a95ae27c TG	50	EXPORT_SYMBOL(vmalloc_base);
25dfe478 TG	51	unsigned long vmemmap_base = __VMEMMAP_BASE;
25dfe478 TG	52	EXPORT_SYMBOL(vmemmap_base);
0483e1fa TG	53
	54	/*
	55	* Memory regions randomized by KASLR (except modules that use a separate logic
	56	* earlier during boot). The list is ordered based on virtual addresses. This
	57	* order is kept after randomization.
	58	*/
	59	static __initdata struct kaslr_memory_region {
	60	unsigned long *base;
	61	unsigned long size_tb;
	62	} kaslr_regions[] = {
8624c1f6	63	{ &page_offset_base, 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT) /* Maximum */ },
a95ae27c	64	{ &vmalloc_base, VMALLOC_SIZE_TB },
25dfe478	65	{ &vmemmap_base, 1 },
0483e1fa TG	66	};
	67
	68	/* Get size in bytes used by the memory region */
	69	static inline unsigned long get_padding(struct kaslr_memory_region *region)
	70	{
	71	return (region->size_tb << TB_SHIFT);
	72	}
	73
	74	/*
	75	* Apply no randomization if KASLR was disabled at boot or if KASAN
	76	* is enabled. KASAN shadow mappings rely on regions being PGD aligned.
	77	*/
	78	static inline bool kaslr_memory_enabled(void)
	79	{
a5ff1b34	80	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
0483e1fa TG	81	}
	82
	83	/* Initialize base and padding for each memory region randomized with KASLR */
	84	void __init kernel_randomize_memory(void)
	85	{
	86	size_t i;
	87	unsigned long vaddr = vaddr_start;
021182e5	88	unsigned long rand, memory_tb;
0483e1fa TG	89	struct rnd_state rand_state;
	90	unsigned long remain_entropy;
	91
25dfe478	92	/*
1dddd251 TG	93	* These BUILD_BUG_ON checks ensure the memory layout is consistent
	94	* with the vaddr_start/vaddr_end variables. These checks are very
	95	* limited....
25dfe478 TG	96	*/
25dfe478 TG	97	BUILD_BUG_ON(vaddr_start >= vaddr_end);
1dddd251	98	BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE);
25dfe478 TG	99	BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
25dfe478 TG	100
0483e1fa TG	101	if (!kaslr_memory_enabled())
	102	return;
	103
90397a41 TG	104	/*
	105	* Update Physical memory mapping to available and
	106	* add padding if needed (especially for memory hotplug support).
	107	*/
021182e5	108	BUG_ON(kaslr_regions[0].base != &page_offset_base);
c7d2361f	109	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
90397a41	110	CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
021182e5 TG	111
	112	/* Adapt phyiscal memory region size based on available memory */
	113	if (memory_tb < kaslr_regions[0].size_tb)
	114	kaslr_regions[0].size_tb = memory_tb;
	115
0483e1fa TG	116	/* Calculate entropy available between regions */
	117	remain_entropy = vaddr_end - vaddr_start;
	118	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
	119	remain_entropy -= get_padding(&kaslr_regions[i]);
	120
	121	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
	122
	123	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
	124	unsigned long entropy;
	125
	126	/*
	127	* Select a random virtual address using the extra entropy
	128	* available.
	129	*/
	130	entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
	131	prandom_bytes_state(&rand_state, &rand, sizeof(rand));
8624c1f6 KS	132	if (IS_ENABLED(CONFIG_X86_5LEVEL))
	133	entropy = (rand % (entropy + 1)) & P4D_MASK;
	134	else
	135	entropy = (rand % (entropy + 1)) & PUD_MASK;
0483e1fa TG	136	vaddr += entropy;
	137	*kaslr_regions[i].base = vaddr;
	138
	139	/*
	140	* Jump the region and add a minimum padding based on
	141	* randomization alignment.
	142	*/
	143	vaddr += get_padding(&kaslr_regions[i]);
8624c1f6 KS	144	if (IS_ENABLED(CONFIG_X86_5LEVEL))
	145	vaddr = round_up(vaddr + 1, P4D_SIZE);
	146	else
	147	vaddr = round_up(vaddr + 1, PUD_SIZE);
0483e1fa TG	148	remain_entropy -= entropy;
	149	}
	150	}
	151
8624c1f6	152	static void __meminit init_trampoline_pud(void)
0483e1fa TG	153	{
	154	unsigned long paddr, paddr_next;
	155	pgd_t *pgd;
	156	pud_t pud_page, pud_page_tramp;
	157	int i;
	158
0483e1fa TG	159	pud_page_tramp = alloc_low_page();
	160
	161	paddr = 0;
	162	pgd = pgd_offset_k((unsigned long)__va(paddr));
	163	pud_page = (pud_t ) pgd_page_vaddr(pgd);
	164
	165	for (i = pud_index(paddr); i < PTRS_PER_PUD; i++, paddr = paddr_next) {
	166	pud_t pud, pud_tramp;
	167	unsigned long vaddr = (unsigned long)__va(paddr);
	168
	169	pud_tramp = pud_page_tramp + pud_index(paddr);
	170	pud = pud_page + pud_index(vaddr);
	171	paddr_next = (paddr & PUD_MASK) + PUD_SIZE;
	172
	173	pud_tramp = pud;
	174	}
	175
	176	set_pgd(&trampoline_pgd_entry,
	177	__pgd(_KERNPG_TABLE \| __pa(pud_page_tramp)));
	178	}
8624c1f6 KS	179
	180	static void __meminit init_trampoline_p4d(void)
	181	{
	182	unsigned long paddr, paddr_next;
	183	pgd_t *pgd;
	184	p4d_t p4d_page, p4d_page_tramp;
	185	int i;
	186
	187	p4d_page_tramp = alloc_low_page();
	188
	189	paddr = 0;
	190	pgd = pgd_offset_k((unsigned long)__va(paddr));
	191	p4d_page = (p4d_t ) pgd_page_vaddr(pgd);
	192
	193	for (i = p4d_index(paddr); i < PTRS_PER_P4D; i++, paddr = paddr_next) {
	194	p4d_t p4d, p4d_tramp;
	195	unsigned long vaddr = (unsigned long)__va(paddr);
	196
	197	p4d_tramp = p4d_page_tramp + p4d_index(paddr);
	198	p4d = p4d_page + p4d_index(vaddr);
	199	paddr_next = (paddr & P4D_MASK) + P4D_SIZE;
	200
	201	p4d_tramp = p4d;
	202	}
	203
	204	set_pgd(&trampoline_pgd_entry,
	205	__pgd(_KERNPG_TABLE \| __pa(p4d_page_tramp)));
	206	}
	207
	208	/*
	209	* Create PGD aligned trampoline table to allow real mode initialization
	210	* of additional CPUs. Consume only 1 low memory page.
	211	*/
	212	void __meminit init_trampoline(void)
	213	{
	214
	215	if (!kaslr_memory_enabled()) {
	216	init_trampoline_default();
	217	return;
	218	}
	219
	220	if (IS_ENABLED(CONFIG_X86_5LEVEL))
	221	init_trampoline_p4d();
	222	else
	223	init_trampoline_pud();
	224	}