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