1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * This code is used on x86_64 to create page table identity mappings on 4 * demand by building up a new set of page tables (or appending to the 5 * existing ones), and then switching over to them when ready. 6 * 7 * Copyright (C) 2015-2016 Yinghai Lu 8 * Copyright (C) 2016 Kees Cook 9 */ 10 11 /* 12 * Since we're dealing with identity mappings, physical and virtual 13 * addresses are the same, so override these defines which are ultimately 14 * used by the headers in misc.h. 15 */ 16 #define __pa(x) ((unsigned long)(x)) 17 #define __va(x) ((void *)((unsigned long)(x))) 18 19 /* No PAGE_TABLE_ISOLATION support needed either: */ 20 #undef CONFIG_PAGE_TABLE_ISOLATION 21 22 #include "error.h" 23 #include "misc.h" 24 25 /* These actually do the work of building the kernel identity maps. */ 26 #include <linux/pgtable.h> 27 #include <asm/cmpxchg.h> 28 #include <asm/trap_pf.h> 29 #include <asm/trapnr.h> 30 #include <asm/init.h> 31 /* Use the static base for this part of the boot process */ 32 #undef __PAGE_OFFSET 33 #define __PAGE_OFFSET __PAGE_OFFSET_BASE 34 #include "../../mm/ident_map.c" 35 36 #define _SETUP 37 #include <asm/setup.h> /* For COMMAND_LINE_SIZE */ 38 #undef _SETUP 39 40 extern unsigned long get_cmd_line_ptr(void); 41 42 /* Used by PAGE_KERN* macros: */ 43 pteval_t __default_kernel_pte_mask __read_mostly = ~0; 44 45 /* Used to track our page table allocation area. */ 46 struct alloc_pgt_data { 47 unsigned char *pgt_buf; 48 unsigned long pgt_buf_size; 49 unsigned long pgt_buf_offset; 50 }; 51 52 /* 53 * Allocates space for a page table entry, using struct alloc_pgt_data 54 * above. Besides the local callers, this is used as the allocation 55 * callback in mapping_info below. 56 */ 57 static void *alloc_pgt_page(void *context) 58 { 59 struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context; 60 unsigned char *entry; 61 62 /* Validate there is space available for a new page. */ 63 if (pages->pgt_buf_offset >= pages->pgt_buf_size) { 64 debug_putstr("out of pgt_buf in " __FILE__ "!?\n"); 65 debug_putaddr(pages->pgt_buf_offset); 66 debug_putaddr(pages->pgt_buf_size); 67 return NULL; 68 } 69 70 entry = pages->pgt_buf + pages->pgt_buf_offset; 71 pages->pgt_buf_offset += PAGE_SIZE; 72 73 return entry; 74 } 75 76 /* Used to track our allocated page tables. */ 77 static struct alloc_pgt_data pgt_data; 78 79 /* The top level page table entry pointer. */ 80 static unsigned long top_level_pgt; 81 82 phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1; 83 84 /* 85 * Mapping information structure passed to kernel_ident_mapping_init(). 86 * Due to relocation, pointers must be assigned at run time not build time. 87 */ 88 static struct x86_mapping_info mapping_info; 89 90 /* 91 * Adds the specified range to the identity mappings. 92 */ 93 static void add_identity_map(unsigned long start, unsigned long end) 94 { 95 int ret; 96 97 /* Align boundary to 2M. */ 98 start = round_down(start, PMD_SIZE); 99 end = round_up(end, PMD_SIZE); 100 if (start >= end) 101 return; 102 103 /* Build the mapping. */ 104 ret = kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt, start, end); 105 if (ret) 106 error("Error: kernel_ident_mapping_init() failed\n"); 107 } 108 109 /* Locates and clears a region for a new top level page table. */ 110 void initialize_identity_maps(void *rmode) 111 { 112 unsigned long cmdline; 113 114 /* Exclude the encryption mask from __PHYSICAL_MASK */ 115 physical_mask &= ~sme_me_mask; 116 117 /* Init mapping_info with run-time function/buffer pointers. */ 118 mapping_info.alloc_pgt_page = alloc_pgt_page; 119 mapping_info.context = &pgt_data; 120 mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask; 121 mapping_info.kernpg_flag = _KERNPG_TABLE; 122 123 /* 124 * It should be impossible for this not to already be true, 125 * but since calling this a second time would rewind the other 126 * counters, let's just make sure this is reset too. 127 */ 128 pgt_data.pgt_buf_offset = 0; 129 130 /* 131 * If we came here via startup_32(), cr3 will be _pgtable already 132 * and we must append to the existing area instead of entirely 133 * overwriting it. 134 * 135 * With 5-level paging, we use '_pgtable' to allocate the p4d page table, 136 * the top-level page table is allocated separately. 137 * 138 * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level 139 * cases. On 4-level paging it's equal to 'top_level_pgt'. 140 */ 141 top_level_pgt = read_cr3_pa(); 142 if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) { 143 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE; 144 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE; 145 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size); 146 } else { 147 pgt_data.pgt_buf = _pgtable; 148 pgt_data.pgt_buf_size = BOOT_PGT_SIZE; 149 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size); 150 top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data); 151 } 152 153 /* 154 * New page-table is set up - map the kernel image, boot_params and the 155 * command line. The uncompressed kernel requires boot_params and the 156 * command line to be mapped in the identity mapping. Map them 157 * explicitly here in case the compressed kernel does not touch them, 158 * or does not touch all the pages covering them. 159 */ 160 add_identity_map((unsigned long)_head, (unsigned long)_end); 161 boot_params = rmode; 162 add_identity_map((unsigned long)boot_params, (unsigned long)(boot_params + 1)); 163 cmdline = get_cmd_line_ptr(); 164 add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE); 165 166 /* Load the new page-table. */ 167 sev_verify_cbit(top_level_pgt); 168 write_cr3(top_level_pgt); 169 } 170 171 static pte_t *split_large_pmd(struct x86_mapping_info *info, 172 pmd_t *pmdp, unsigned long __address) 173 { 174 unsigned long page_flags; 175 unsigned long address; 176 pte_t *pte; 177 pmd_t pmd; 178 int i; 179 180 pte = (pte_t *)info->alloc_pgt_page(info->context); 181 if (!pte) 182 return NULL; 183 184 address = __address & PMD_MASK; 185 /* No large page - clear PSE flag */ 186 page_flags = info->page_flag & ~_PAGE_PSE; 187 188 /* Populate the PTEs */ 189 for (i = 0; i < PTRS_PER_PMD; i++) { 190 set_pte(&pte[i], __pte(address | page_flags)); 191 address += PAGE_SIZE; 192 } 193 194 /* 195 * Ideally we need to clear the large PMD first and do a TLB 196 * flush before we write the new PMD. But the 2M range of the 197 * PMD might contain the code we execute and/or the stack 198 * we are on, so we can't do that. But that should be safe here 199 * because we are going from large to small mappings and we are 200 * also the only user of the page-table, so there is no chance 201 * of a TLB multihit. 202 */ 203 pmd = __pmd((unsigned long)pte | info->kernpg_flag); 204 set_pmd(pmdp, pmd); 205 /* Flush TLB to establish the new PMD */ 206 write_cr3(top_level_pgt); 207 208 return pte + pte_index(__address); 209 } 210 211 static void clflush_page(unsigned long address) 212 { 213 unsigned int flush_size; 214 char *cl, *start, *end; 215 216 /* 217 * Hardcode cl-size to 64 - CPUID can't be used here because that might 218 * cause another #VC exception and the GHCB is not ready to use yet. 219 */ 220 flush_size = 64; 221 start = (char *)(address & PAGE_MASK); 222 end = start + PAGE_SIZE; 223 224 /* 225 * First make sure there are no pending writes on the cache-lines to 226 * flush. 227 */ 228 asm volatile("mfence" : : : "memory"); 229 230 for (cl = start; cl != end; cl += flush_size) 231 clflush(cl); 232 } 233 234 static int set_clr_page_flags(struct x86_mapping_info *info, 235 unsigned long address, 236 pteval_t set, pteval_t clr) 237 { 238 pgd_t *pgdp = (pgd_t *)top_level_pgt; 239 p4d_t *p4dp; 240 pud_t *pudp; 241 pmd_t *pmdp; 242 pte_t *ptep, pte; 243 244 /* 245 * First make sure there is a PMD mapping for 'address'. 246 * It should already exist, but keep things generic. 247 * 248 * To map the page just read from it and fault it in if there is no 249 * mapping yet. add_identity_map() can't be called here because that 250 * would unconditionally map the address on PMD level, destroying any 251 * PTE-level mappings that might already exist. Use assembly here so 252 * the access won't be optimized away. 253 */ 254 asm volatile("mov %[address], %%r9" 255 :: [address] "g" (*(unsigned long *)address) 256 : "r9", "memory"); 257 258 /* 259 * The page is mapped at least with PMD size - so skip checks and walk 260 * directly to the PMD. 261 */ 262 p4dp = p4d_offset(pgdp, address); 263 pudp = pud_offset(p4dp, address); 264 pmdp = pmd_offset(pudp, address); 265 266 if (pmd_large(*pmdp)) 267 ptep = split_large_pmd(info, pmdp, address); 268 else 269 ptep = pte_offset_kernel(pmdp, address); 270 271 if (!ptep) 272 return -ENOMEM; 273 274 /* 275 * Changing encryption attributes of a page requires to flush it from 276 * the caches. 277 */ 278 if ((set | clr) & _PAGE_ENC) 279 clflush_page(address); 280 281 /* Update PTE */ 282 pte = *ptep; 283 pte = pte_set_flags(pte, set); 284 pte = pte_clear_flags(pte, clr); 285 set_pte(ptep, pte); 286 287 /* Flush TLB after changing encryption attribute */ 288 write_cr3(top_level_pgt); 289 290 return 0; 291 } 292 293 int set_page_decrypted(unsigned long address) 294 { 295 return set_clr_page_flags(&mapping_info, address, 0, _PAGE_ENC); 296 } 297 298 int set_page_encrypted(unsigned long address) 299 { 300 return set_clr_page_flags(&mapping_info, address, _PAGE_ENC, 0); 301 } 302 303 int set_page_non_present(unsigned long address) 304 { 305 return set_clr_page_flags(&mapping_info, address, 0, _PAGE_PRESENT); 306 } 307 308 static void do_pf_error(const char *msg, unsigned long error_code, 309 unsigned long address, unsigned long ip) 310 { 311 error_putstr(msg); 312 313 error_putstr("\nError Code: "); 314 error_puthex(error_code); 315 error_putstr("\nCR2: 0x"); 316 error_puthex(address); 317 error_putstr("\nRIP relative to _head: 0x"); 318 error_puthex(ip - (unsigned long)_head); 319 error_putstr("\n"); 320 321 error("Stopping.\n"); 322 } 323 324 void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code) 325 { 326 unsigned long address = native_read_cr2(); 327 unsigned long end; 328 bool ghcb_fault; 329 330 ghcb_fault = sev_es_check_ghcb_fault(address); 331 332 address &= PMD_MASK; 333 end = address + PMD_SIZE; 334 335 /* 336 * Check for unexpected error codes. Unexpected are: 337 * - Faults on present pages 338 * - User faults 339 * - Reserved bits set 340 */ 341 if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD)) 342 do_pf_error("Unexpected page-fault:", error_code, address, regs->ip); 343 else if (ghcb_fault) 344 do_pf_error("Page-fault on GHCB page:", error_code, address, regs->ip); 345 346 /* 347 * Error code is sane - now identity map the 2M region around 348 * the faulting address. 349 */ 350 add_identity_map(address, end); 351 } 352