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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
40extern unsigned long get_cmd_line_ptr(void);
41
42/* Used by PAGE_KERN* macros: */
43pteval_t __default_kernel_pte_mask __read_mostly = ~0;
44
45/* Used to track our page table allocation area. */
46struct 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 */
57static 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. */
77static struct alloc_pgt_data pgt_data;
78
79/* The top level page table entry pointer. */
80static unsigned long top_level_pgt;
81
82phys_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 */
88static struct x86_mapping_info mapping_info;
89
90/*
91 * Adds the specified range to the identity mappings.
92 */
93void kernel_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. */
110void initialize_identity_maps(void *rmode)
111{
112 unsigned long cmdline;
113 struct setup_data *sd;
114
115 /* Exclude the encryption mask from __PHYSICAL_MASK */
116 physical_mask &= ~sme_me_mask;
117
118 /* Init mapping_info with run-time function/buffer pointers. */
119 mapping_info.alloc_pgt_page = alloc_pgt_page;
120 mapping_info.context = &pgt_data;
121 mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
122 mapping_info.kernpg_flag = _KERNPG_TABLE;
123
124 /*
125 * It should be impossible for this not to already be true,
126 * but since calling this a second time would rewind the other
127 * counters, let's just make sure this is reset too.
128 */
129 pgt_data.pgt_buf_offset = 0;
130
131 /*
132 * If we came here via startup_32(), cr3 will be _pgtable already
133 * and we must append to the existing area instead of entirely
134 * overwriting it.
135 *
136 * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
137 * the top-level page table is allocated separately.
138 *
139 * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
140 * cases. On 4-level paging it's equal to 'top_level_pgt'.
141 */
142 top_level_pgt = read_cr3_pa();
143 if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
144 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
145 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
146 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
147 } else {
148 pgt_data.pgt_buf = _pgtable;
149 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
150 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
151 top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
152 }
153
154 /*
155 * New page-table is set up - map the kernel image, boot_params and the
156 * command line. The uncompressed kernel requires boot_params and the
157 * command line to be mapped in the identity mapping. Map them
158 * explicitly here in case the compressed kernel does not touch them,
159 * or does not touch all the pages covering them.
160 */
161 kernel_add_identity_map((unsigned long)_head, (unsigned long)_end);
162 boot_params = rmode;
163 kernel_add_identity_map((unsigned long)boot_params, (unsigned long)(boot_params + 1));
164 cmdline = get_cmd_line_ptr();
165 kernel_add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
166
167 /*
168 * Also map the setup_data entries passed via boot_params in case they
169 * need to be accessed by uncompressed kernel via the identity mapping.
170 */
171 sd = (struct setup_data *)boot_params->hdr.setup_data;
172 while (sd) {
173 unsigned long sd_addr = (unsigned long)sd;
174
175 kernel_add_identity_map(sd_addr, sd_addr + sizeof(*sd) + sd->len);
176 sd = (struct setup_data *)sd->next;
177 }
178
179 sev_prep_identity_maps(top_level_pgt);
180
181 /* Load the new page-table. */
182 write_cr3(top_level_pgt);
183
184 /*
185 * Now that the required page table mappings are established and a
186 * GHCB can be used, check for SNP guest/HV feature compatibility.
187 */
188 snp_check_features();
189}
190
191static pte_t *split_large_pmd(struct x86_mapping_info *info,
192 pmd_t *pmdp, unsigned long __address)
193{
194 unsigned long page_flags;
195 unsigned long address;
196 pte_t *pte;
197 pmd_t pmd;
198 int i;
199
200 pte = (pte_t *)info->alloc_pgt_page(info->context);
201 if (!pte)
202 return NULL;
203
204 address = __address & PMD_MASK;
205 /* No large page - clear PSE flag */
206 page_flags = info->page_flag & ~_PAGE_PSE;
207
208 /* Populate the PTEs */
209 for (i = 0; i < PTRS_PER_PMD; i++) {
210 set_pte(&pte[i], __pte(address | page_flags));
211 address += PAGE_SIZE;
212 }
213
214 /*
215 * Ideally we need to clear the large PMD first and do a TLB
216 * flush before we write the new PMD. But the 2M range of the
217 * PMD might contain the code we execute and/or the stack
218 * we are on, so we can't do that. But that should be safe here
219 * because we are going from large to small mappings and we are
220 * also the only user of the page-table, so there is no chance
221 * of a TLB multihit.
222 */
223 pmd = __pmd((unsigned long)pte | info->kernpg_flag);
224 set_pmd(pmdp, pmd);
225 /* Flush TLB to establish the new PMD */
226 write_cr3(top_level_pgt);
227
228 return pte + pte_index(__address);
229}
230
231static void clflush_page(unsigned long address)
232{
233 unsigned int flush_size;
234 char *cl, *start, *end;
235
236 /*
237 * Hardcode cl-size to 64 - CPUID can't be used here because that might
238 * cause another #VC exception and the GHCB is not ready to use yet.
239 */
240 flush_size = 64;
241 start = (char *)(address & PAGE_MASK);
242 end = start + PAGE_SIZE;
243
244 /*
245 * First make sure there are no pending writes on the cache-lines to
246 * flush.
247 */
248 asm volatile("mfence" : : : "memory");
249
250 for (cl = start; cl != end; cl += flush_size)
251 clflush(cl);
252}
253
254static int set_clr_page_flags(struct x86_mapping_info *info,
255 unsigned long address,
256 pteval_t set, pteval_t clr)
257{
258 pgd_t *pgdp = (pgd_t *)top_level_pgt;
259 p4d_t *p4dp;
260 pud_t *pudp;
261 pmd_t *pmdp;
262 pte_t *ptep, pte;
263
264 /*
265 * First make sure there is a PMD mapping for 'address'.
266 * It should already exist, but keep things generic.
267 *
268 * To map the page just read from it and fault it in if there is no
269 * mapping yet. kernel_add_identity_map() can't be called here because
270 * that would unconditionally map the address on PMD level, destroying
271 * any PTE-level mappings that might already exist. Use assembly here
272 * so the access won't be optimized away.
273 */
274 asm volatile("mov %[address], %%r9"
275 :: [address] "g" (*(unsigned long *)address)
276 : "r9", "memory");
277
278 /*
279 * The page is mapped at least with PMD size - so skip checks and walk
280 * directly to the PMD.
281 */
282 p4dp = p4d_offset(pgdp, address);
283 pudp = pud_offset(p4dp, address);
284 pmdp = pmd_offset(pudp, address);
285
286 if (pmd_large(*pmdp))
287 ptep = split_large_pmd(info, pmdp, address);
288 else
289 ptep = pte_offset_kernel(pmdp, address);
290
291 if (!ptep)
292 return -ENOMEM;
293
294 /*
295 * Changing encryption attributes of a page requires to flush it from
296 * the caches.
297 */
298 if ((set | clr) & _PAGE_ENC) {
299 clflush_page(address);
300
301 /*
302 * If the encryption attribute is being cleared, change the page state
303 * to shared in the RMP table.
304 */
305 if (clr)
306 snp_set_page_shared(__pa(address & PAGE_MASK));
307 }
308
309 /* Update PTE */
310 pte = *ptep;
311 pte = pte_set_flags(pte, set);
312 pte = pte_clear_flags(pte, clr);
313 set_pte(ptep, pte);
314
315 /*
316 * If the encryption attribute is being set, then change the page state to
317 * private in the RMP entry. The page state change must be done after the PTE
318 * is updated.
319 */
320 if (set & _PAGE_ENC)
321 snp_set_page_private(__pa(address & PAGE_MASK));
322
323 /* Flush TLB after changing encryption attribute */
324 write_cr3(top_level_pgt);
325
326 return 0;
327}
328
329int set_page_decrypted(unsigned long address)
330{
331 return set_clr_page_flags(&mapping_info, address, 0, _PAGE_ENC);
332}
333
334int set_page_encrypted(unsigned long address)
335{
336 return set_clr_page_flags(&mapping_info, address, _PAGE_ENC, 0);
337}
338
339int set_page_non_present(unsigned long address)
340{
341 return set_clr_page_flags(&mapping_info, address, 0, _PAGE_PRESENT);
342}
343
344static void do_pf_error(const char *msg, unsigned long error_code,
345 unsigned long address, unsigned long ip)
346{
347 error_putstr(msg);
348
349 error_putstr("\nError Code: ");
350 error_puthex(error_code);
351 error_putstr("\nCR2: 0x");
352 error_puthex(address);
353 error_putstr("\nRIP relative to _head: 0x");
354 error_puthex(ip - (unsigned long)_head);
355 error_putstr("\n");
356
357 error("Stopping.\n");
358}
359
360void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
361{
362 unsigned long address = native_read_cr2();
363 unsigned long end;
364 bool ghcb_fault;
365
366 ghcb_fault = sev_es_check_ghcb_fault(address);
367
368 address &= PMD_MASK;
369 end = address + PMD_SIZE;
370
371 /*
372 * Check for unexpected error codes. Unexpected are:
373 * - Faults on present pages
374 * - User faults
375 * - Reserved bits set
376 */
377 if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD))
378 do_pf_error("Unexpected page-fault:", error_code, address, regs->ip);
379 else if (ghcb_fault)
380 do_pf_error("Page-fault on GHCB page:", error_code, address, regs->ip);
381
382 /*
383 * Error code is sane - now identity map the 2M region around
384 * the faulting address.
385 */
386 kernel_add_identity_map(address, end);
387}