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 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 static pte_t *split_large_pmd(struct x86_mapping_info *info,
186 			      pmd_t *pmdp, unsigned long __address)
187 {
188 	unsigned long page_flags;
189 	unsigned long address;
190 	pte_t *pte;
191 	pmd_t pmd;
192 	int i;
193 
194 	pte = (pte_t *)info->alloc_pgt_page(info->context);
195 	if (!pte)
196 		return NULL;
197 
198 	address     = __address & PMD_MASK;
199 	/* No large page - clear PSE flag */
200 	page_flags  = info->page_flag & ~_PAGE_PSE;
201 
202 	/* Populate the PTEs */
203 	for (i = 0; i < PTRS_PER_PMD; i++) {
204 		set_pte(&pte[i], __pte(address | page_flags));
205 		address += PAGE_SIZE;
206 	}
207 
208 	/*
209 	 * Ideally we need to clear the large PMD first and do a TLB
210 	 * flush before we write the new PMD. But the 2M range of the
211 	 * PMD might contain the code we execute and/or the stack
212 	 * we are on, so we can't do that. But that should be safe here
213 	 * because we are going from large to small mappings and we are
214 	 * also the only user of the page-table, so there is no chance
215 	 * of a TLB multihit.
216 	 */
217 	pmd = __pmd((unsigned long)pte | info->kernpg_flag);
218 	set_pmd(pmdp, pmd);
219 	/* Flush TLB to establish the new PMD */
220 	write_cr3(top_level_pgt);
221 
222 	return pte + pte_index(__address);
223 }
224 
225 static void clflush_page(unsigned long address)
226 {
227 	unsigned int flush_size;
228 	char *cl, *start, *end;
229 
230 	/*
231 	 * Hardcode cl-size to 64 - CPUID can't be used here because that might
232 	 * cause another #VC exception and the GHCB is not ready to use yet.
233 	 */
234 	flush_size = 64;
235 	start      = (char *)(address & PAGE_MASK);
236 	end        = start + PAGE_SIZE;
237 
238 	/*
239 	 * First make sure there are no pending writes on the cache-lines to
240 	 * flush.
241 	 */
242 	asm volatile("mfence" : : : "memory");
243 
244 	for (cl = start; cl != end; cl += flush_size)
245 		clflush(cl);
246 }
247 
248 static int set_clr_page_flags(struct x86_mapping_info *info,
249 			      unsigned long address,
250 			      pteval_t set, pteval_t clr)
251 {
252 	pgd_t *pgdp = (pgd_t *)top_level_pgt;
253 	p4d_t *p4dp;
254 	pud_t *pudp;
255 	pmd_t *pmdp;
256 	pte_t *ptep, pte;
257 
258 	/*
259 	 * First make sure there is a PMD mapping for 'address'.
260 	 * It should already exist, but keep things generic.
261 	 *
262 	 * To map the page just read from it and fault it in if there is no
263 	 * mapping yet. kernel_add_identity_map() can't be called here because
264 	 * that would unconditionally map the address on PMD level, destroying
265 	 * any PTE-level mappings that might already exist. Use assembly here
266 	 * so the access won't be optimized away.
267 	 */
268 	asm volatile("mov %[address], %%r9"
269 		     :: [address] "g" (*(unsigned long *)address)
270 		     : "r9", "memory");
271 
272 	/*
273 	 * The page is mapped at least with PMD size - so skip checks and walk
274 	 * directly to the PMD.
275 	 */
276 	p4dp = p4d_offset(pgdp, address);
277 	pudp = pud_offset(p4dp, address);
278 	pmdp = pmd_offset(pudp, address);
279 
280 	if (pmd_large(*pmdp))
281 		ptep = split_large_pmd(info, pmdp, address);
282 	else
283 		ptep = pte_offset_kernel(pmdp, address);
284 
285 	if (!ptep)
286 		return -ENOMEM;
287 
288 	/*
289 	 * Changing encryption attributes of a page requires to flush it from
290 	 * the caches.
291 	 */
292 	if ((set | clr) & _PAGE_ENC) {
293 		clflush_page(address);
294 
295 		/*
296 		 * If the encryption attribute is being cleared, change the page state
297 		 * to shared in the RMP table.
298 		 */
299 		if (clr)
300 			snp_set_page_shared(__pa(address & PAGE_MASK));
301 	}
302 
303 	/* Update PTE */
304 	pte = *ptep;
305 	pte = pte_set_flags(pte, set);
306 	pte = pte_clear_flags(pte, clr);
307 	set_pte(ptep, pte);
308 
309 	/*
310 	 * If the encryption attribute is being set, then change the page state to
311 	 * private in the RMP entry. The page state change must be done after the PTE
312 	 * is updated.
313 	 */
314 	if (set & _PAGE_ENC)
315 		snp_set_page_private(__pa(address & PAGE_MASK));
316 
317 	/* Flush TLB after changing encryption attribute */
318 	write_cr3(top_level_pgt);
319 
320 	return 0;
321 }
322 
323 int set_page_decrypted(unsigned long address)
324 {
325 	return set_clr_page_flags(&mapping_info, address, 0, _PAGE_ENC);
326 }
327 
328 int set_page_encrypted(unsigned long address)
329 {
330 	return set_clr_page_flags(&mapping_info, address, _PAGE_ENC, 0);
331 }
332 
333 int set_page_non_present(unsigned long address)
334 {
335 	return set_clr_page_flags(&mapping_info, address, 0, _PAGE_PRESENT);
336 }
337 
338 static void do_pf_error(const char *msg, unsigned long error_code,
339 			unsigned long address, unsigned long ip)
340 {
341 	error_putstr(msg);
342 
343 	error_putstr("\nError Code: ");
344 	error_puthex(error_code);
345 	error_putstr("\nCR2: 0x");
346 	error_puthex(address);
347 	error_putstr("\nRIP relative to _head: 0x");
348 	error_puthex(ip - (unsigned long)_head);
349 	error_putstr("\n");
350 
351 	error("Stopping.\n");
352 }
353 
354 void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
355 {
356 	unsigned long address = native_read_cr2();
357 	unsigned long end;
358 	bool ghcb_fault;
359 
360 	ghcb_fault = sev_es_check_ghcb_fault(address);
361 
362 	address   &= PMD_MASK;
363 	end        = address + PMD_SIZE;
364 
365 	/*
366 	 * Check for unexpected error codes. Unexpected are:
367 	 *	- Faults on present pages
368 	 *	- User faults
369 	 *	- Reserved bits set
370 	 */
371 	if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD))
372 		do_pf_error("Unexpected page-fault:", error_code, address, regs->ip);
373 	else if (ghcb_fault)
374 		do_pf_error("Page-fault on GHCB page:", error_code, address, regs->ip);
375 
376 	/*
377 	 * Error code is sane - now identity map the 2M region around
378 	 * the faulting address.
379 	 */
380 	kernel_add_identity_map(address, end);
381 }
382