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