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 /* No PAGE_TABLE_ISOLATION support needed either: */
12 #undef CONFIG_PAGE_TABLE_ISOLATION
13 
14 #include "error.h"
15 #include "misc.h"
16 
17 /* These actually do the work of building the kernel identity maps. */
18 #include <linux/pgtable.h>
19 #include <asm/cmpxchg.h>
20 #include <asm/trap_pf.h>
21 #include <asm/trapnr.h>
22 #include <asm/init.h>
23 /* Use the static base for this part of the boot process */
24 #undef __PAGE_OFFSET
25 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
26 #include "../../mm/ident_map.c"
27 
28 #define _SETUP
29 #include <asm/setup.h>	/* For COMMAND_LINE_SIZE */
30 #undef _SETUP
31 
32 extern unsigned long get_cmd_line_ptr(void);
33 
34 /* Used by PAGE_KERN* macros: */
35 pteval_t __default_kernel_pte_mask __read_mostly = ~0;
36 
37 /* Used to track our page table allocation area. */
38 struct alloc_pgt_data {
39 	unsigned char *pgt_buf;
40 	unsigned long pgt_buf_size;
41 	unsigned long pgt_buf_offset;
42 };
43 
44 /*
45  * Allocates space for a page table entry, using struct alloc_pgt_data
46  * above. Besides the local callers, this is used as the allocation
47  * callback in mapping_info below.
48  */
49 static void *alloc_pgt_page(void *context)
50 {
51 	struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
52 	unsigned char *entry;
53 
54 	/* Validate there is space available for a new page. */
55 	if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
56 		debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
57 		debug_putaddr(pages->pgt_buf_offset);
58 		debug_putaddr(pages->pgt_buf_size);
59 		return NULL;
60 	}
61 
62 	/* Consumed more tables than expected? */
63 	if (pages->pgt_buf_offset == BOOT_PGT_SIZE_WARN) {
64 		debug_putstr("pgt_buf running low in " __FILE__ "\n");
65 		debug_putstr("Need to raise BOOT_PGT_SIZE?\n");
66 		debug_putaddr(pages->pgt_buf_offset);
67 		debug_putaddr(pages->pgt_buf_size);
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 void 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. */
110 void 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 
191 static 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 
231 static 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 
254 static 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 
329 int set_page_decrypted(unsigned long address)
330 {
331 	return set_clr_page_flags(&mapping_info, address, 0, _PAGE_ENC);
332 }
333 
334 int set_page_encrypted(unsigned long address)
335 {
336 	return set_clr_page_flags(&mapping_info, address, _PAGE_ENC, 0);
337 }
338 
339 int set_page_non_present(unsigned long address)
340 {
341 	return set_clr_page_flags(&mapping_info, address, 0, _PAGE_PRESENT);
342 }
343 
344 static 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 
360 void 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 }
388