1 // SPDX-License-Identifier: GPL-2.0
2 #include "misc.h"
3 #include <asm/e820/types.h>
4 #include <asm/processor.h>
5 #include "pgtable.h"
6 #include "../string.h"
7 #include "efi.h"
8 
9 #define BIOS_START_MIN		0x20000U	/* 128K, less than this is insane */
10 #define BIOS_START_MAX		0x9f000U	/* 640K, absolute maximum */
11 
12 #ifdef CONFIG_X86_5LEVEL
13 /* __pgtable_l5_enabled needs to be in .data to avoid being cleared along with .bss */
14 unsigned int __section(".data") __pgtable_l5_enabled;
15 unsigned int __section(".data") pgdir_shift = 39;
16 unsigned int __section(".data") ptrs_per_p4d = 1;
17 #endif
18 
19 struct paging_config {
20 	unsigned long trampoline_start;
21 	unsigned long l5_required;
22 };
23 
24 /* Buffer to preserve trampoline memory */
25 static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
26 
27 /*
28  * Trampoline address will be printed by extract_kernel() for debugging
29  * purposes.
30  *
31  * Avoid putting the pointer into .bss as it will be cleared between
32  * paging_prepare() and extract_kernel().
33  */
34 unsigned long *trampoline_32bit __section(".data");
35 
36 extern struct boot_params *boot_params;
37 int cmdline_find_option_bool(const char *option);
38 
find_trampoline_placement(void)39 static unsigned long find_trampoline_placement(void)
40 {
41 	unsigned long bios_start = 0, ebda_start = 0;
42 	struct boot_e820_entry *entry;
43 	char *signature;
44 	int i;
45 
46 	/*
47 	 * Find a suitable spot for the trampoline.
48 	 * This code is based on reserve_bios_regions().
49 	 */
50 
51 	/*
52 	 * EFI systems may not provide legacy ROM. The memory may not be mapped
53 	 * at all.
54 	 *
55 	 * Only look for values in the legacy ROM for non-EFI system.
56 	 */
57 	signature = (char *)&boot_params->efi_info.efi_loader_signature;
58 	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
59 	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4)) {
60 		ebda_start = *(unsigned short *)0x40e << 4;
61 		bios_start = *(unsigned short *)0x413 << 10;
62 	}
63 
64 	if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
65 		bios_start = BIOS_START_MAX;
66 
67 	if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)
68 		bios_start = ebda_start;
69 
70 	bios_start = round_down(bios_start, PAGE_SIZE);
71 
72 	/* Find the first usable memory region under bios_start. */
73 	for (i = boot_params->e820_entries - 1; i >= 0; i--) {
74 		unsigned long new = bios_start;
75 
76 		entry = &boot_params->e820_table[i];
77 
78 		/* Skip all entries above bios_start. */
79 		if (bios_start <= entry->addr)
80 			continue;
81 
82 		/* Skip non-RAM entries. */
83 		if (entry->type != E820_TYPE_RAM)
84 			continue;
85 
86 		/* Adjust bios_start to the end of the entry if needed. */
87 		if (bios_start > entry->addr + entry->size)
88 			new = entry->addr + entry->size;
89 
90 		/* Keep bios_start page-aligned. */
91 		new = round_down(new, PAGE_SIZE);
92 
93 		/* Skip the entry if it's too small. */
94 		if (new - TRAMPOLINE_32BIT_SIZE < entry->addr)
95 			continue;
96 
97 		/* Protect against underflow. */
98 		if (new - TRAMPOLINE_32BIT_SIZE > bios_start)
99 			break;
100 
101 		bios_start = new;
102 		break;
103 	}
104 
105 	/* Place the trampoline just below the end of low memory */
106 	return bios_start - TRAMPOLINE_32BIT_SIZE;
107 }
108 
paging_prepare(void * rmode)109 struct paging_config paging_prepare(void *rmode)
110 {
111 	struct paging_config paging_config = {};
112 
113 	/* Initialize boot_params. Required for cmdline_find_option_bool(). */
114 	boot_params = rmode;
115 
116 	/*
117 	 * Check if LA57 is desired and supported.
118 	 *
119 	 * There are several parts to the check:
120 	 *   - if the kernel supports 5-level paging: CONFIG_X86_5LEVEL=y
121 	 *   - if user asked to disable 5-level paging: no5lvl in cmdline
122 	 *   - if the machine supports 5-level paging:
123 	 *     + CPUID leaf 7 is supported
124 	 *     + the leaf has the feature bit set
125 	 *
126 	 * That's substitute for boot_cpu_has() in early boot code.
127 	 */
128 	if (IS_ENABLED(CONFIG_X86_5LEVEL) &&
129 			!cmdline_find_option_bool("no5lvl") &&
130 			native_cpuid_eax(0) >= 7 &&
131 			(native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) {
132 		paging_config.l5_required = 1;
133 	}
134 
135 	paging_config.trampoline_start = find_trampoline_placement();
136 
137 	trampoline_32bit = (unsigned long *)paging_config.trampoline_start;
138 
139 	/* Preserve trampoline memory */
140 	memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
141 
142 	/* Clear trampoline memory first */
143 	memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
144 
145 	/* Copy trampoline code in place */
146 	memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
147 			&trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);
148 
149 	/*
150 	 * The code below prepares page table in trampoline memory.
151 	 *
152 	 * The new page table will be used by trampoline code for switching
153 	 * from 4- to 5-level paging or vice versa.
154 	 *
155 	 * If switching is not required, the page table is unused: trampoline
156 	 * code wouldn't touch CR3.
157 	 */
158 
159 	/*
160 	 * We are not going to use the page table in trampoline memory if we
161 	 * are already in the desired paging mode.
162 	 */
163 	if (paging_config.l5_required == !!(native_read_cr4() & X86_CR4_LA57))
164 		goto out;
165 
166 	if (paging_config.l5_required) {
167 		/*
168 		 * For 4- to 5-level paging transition, set up current CR3 as
169 		 * the first and the only entry in a new top-level page table.
170 		 */
171 		trampoline_32bit[TRAMPOLINE_32BIT_PGTABLE_OFFSET] = __native_read_cr3() | _PAGE_TABLE_NOENC;
172 	} else {
173 		unsigned long src;
174 
175 		/*
176 		 * For 5- to 4-level paging transition, copy page table pointed
177 		 * by first entry in the current top-level page table as our
178 		 * new top-level page table.
179 		 *
180 		 * We cannot just point to the page table from trampoline as it
181 		 * may be above 4G.
182 		 */
183 		src = *(unsigned long *)__native_read_cr3() & PAGE_MASK;
184 		memcpy(trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long),
185 		       (void *)src, PAGE_SIZE);
186 	}
187 
188 out:
189 	return paging_config;
190 }
191 
cleanup_trampoline(void * pgtable)192 void cleanup_trampoline(void *pgtable)
193 {
194 	void *trampoline_pgtable;
195 
196 	trampoline_pgtable = trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);
197 
198 	/*
199 	 * Move the top level page table out of trampoline memory,
200 	 * if it's there.
201 	 */
202 	if ((void *)__native_read_cr3() == trampoline_pgtable) {
203 		memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
204 		native_write_cr3((unsigned long)pgtable);
205 	}
206 
207 	/* Restore trampoline memory */
208 	memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
209 
210 	/* Initialize variables for 5-level paging */
211 #ifdef CONFIG_X86_5LEVEL
212 	if (__read_cr4() & X86_CR4_LA57) {
213 		__pgtable_l5_enabled = 1;
214 		pgdir_shift = 48;
215 		ptrs_per_p4d = 512;
216 	}
217 #endif
218 }
219