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 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 } 103 104 struct 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 } 182 183 out: 184 return paging_config; 185 } 186 187 void 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