xref: /linux/arch/arm64/kernel/vdso.c (revision 9025cebf12d1763de36d5e09e2b0a1e4f9b13b28) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * VDSO implementations.
4  *
5  * Copyright (C) 2012 ARM Limited
6  *
7  * Author: Will Deacon <will.deacon@arm.com>
8  */
9 
10 #include <linux/cache.h>
11 #include <linux/clocksource.h>
12 #include <linux/elf.h>
13 #include <linux/err.h>
14 #include <linux/errno.h>
15 #include <linux/gfp.h>
16 #include <linux/kernel.h>
17 #include <linux/mm.h>
18 #include <linux/sched.h>
19 #include <linux/signal.h>
20 #include <linux/slab.h>
21 #include <linux/time_namespace.h>
22 #include <linux/timekeeper_internal.h>
23 #include <linux/vmalloc.h>
24 #include <vdso/datapage.h>
25 #include <vdso/helpers.h>
26 #include <vdso/vsyscall.h>
27 
28 #include <asm/cacheflush.h>
29 #include <asm/signal32.h>
30 #include <asm/vdso.h>
31 
32 enum vdso_abi {
33 	VDSO_ABI_AA64,
34 	VDSO_ABI_AA32,
35 };
36 
37 enum vvar_pages {
38 	VVAR_DATA_PAGE_OFFSET,
39 	VVAR_TIMENS_PAGE_OFFSET,
40 	VVAR_NR_PAGES,
41 };
42 
43 struct vdso_abi_info {
44 	const char *name;
45 	const char *vdso_code_start;
46 	const char *vdso_code_end;
47 	unsigned long vdso_pages;
48 	/* Data Mapping */
49 	struct vm_special_mapping *dm;
50 	/* Code Mapping */
51 	struct vm_special_mapping *cm;
52 };
53 
54 static struct vdso_abi_info vdso_info[] __ro_after_init = {
55 	[VDSO_ABI_AA64] = {
56 		.name = "vdso",
57 		.vdso_code_start = vdso_start,
58 		.vdso_code_end = vdso_end,
59 	},
60 #ifdef CONFIG_COMPAT_VDSO
61 	[VDSO_ABI_AA32] = {
62 		.name = "vdso32",
63 		.vdso_code_start = vdso32_start,
64 		.vdso_code_end = vdso32_end,
65 	},
66 #endif /* CONFIG_COMPAT_VDSO */
67 };
68 
69 /*
70  * The vDSO data page.
71  */
72 static union {
73 	struct vdso_data	data[CS_BASES];
74 	u8			page[PAGE_SIZE];
75 } vdso_data_store __page_aligned_data;
76 struct vdso_data *vdso_data = vdso_data_store.data;
77 
78 static int vdso_mremap(const struct vm_special_mapping *sm,
79 		struct vm_area_struct *new_vma)
80 {
81 	current->mm->context.vdso = (void *)new_vma->vm_start;
82 
83 	return 0;
84 }
85 
86 static int __init __vdso_init(enum vdso_abi abi)
87 {
88 	int i;
89 	struct page **vdso_pagelist;
90 	unsigned long pfn;
91 
92 	if (memcmp(vdso_info[abi].vdso_code_start, "\177ELF", 4)) {
93 		pr_err("vDSO is not a valid ELF object!\n");
94 		return -EINVAL;
95 	}
96 
97 	vdso_info[abi].vdso_pages = (
98 			vdso_info[abi].vdso_code_end -
99 			vdso_info[abi].vdso_code_start) >>
100 			PAGE_SHIFT;
101 
102 	vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages,
103 				sizeof(struct page *),
104 				GFP_KERNEL);
105 	if (vdso_pagelist == NULL)
106 		return -ENOMEM;
107 
108 	/* Grab the vDSO code pages. */
109 	pfn = sym_to_pfn(vdso_info[abi].vdso_code_start);
110 
111 	for (i = 0; i < vdso_info[abi].vdso_pages; i++)
112 		vdso_pagelist[i] = pfn_to_page(pfn + i);
113 
114 	vdso_info[abi].cm->pages = vdso_pagelist;
115 
116 	return 0;
117 }
118 
119 #ifdef CONFIG_TIME_NS
120 struct vdso_data *arch_get_vdso_data(void *vvar_page)
121 {
122 	return (struct vdso_data *)(vvar_page);
123 }
124 
125 /*
126  * The vvar mapping contains data for a specific time namespace, so when a task
127  * changes namespace we must unmap its vvar data for the old namespace.
128  * Subsequent faults will map in data for the new namespace.
129  *
130  * For more details see timens_setup_vdso_data().
131  */
132 int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
133 {
134 	struct mm_struct *mm = task->mm;
135 	struct vm_area_struct *vma;
136 
137 	mmap_read_lock(mm);
138 
139 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
140 		unsigned long size = vma->vm_end - vma->vm_start;
141 
142 		if (vma_is_special_mapping(vma, vdso_info[VDSO_ABI_AA64].dm))
143 			zap_page_range(vma, vma->vm_start, size);
144 #ifdef CONFIG_COMPAT_VDSO
145 		if (vma_is_special_mapping(vma, vdso_info[VDSO_ABI_AA32].dm))
146 			zap_page_range(vma, vma->vm_start, size);
147 #endif
148 	}
149 
150 	mmap_read_unlock(mm);
151 	return 0;
152 }
153 
154 static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
155 {
156 	if (likely(vma->vm_mm == current->mm))
157 		return current->nsproxy->time_ns->vvar_page;
158 
159 	/*
160 	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
161 	 * through interfaces like /proc/$pid/mem or
162 	 * process_vm_{readv,writev}() as long as there's no .access()
163 	 * in special_mapping_vmops.
164 	 * For more details check_vma_flags() and __access_remote_vm()
165 	 */
166 	WARN(1, "vvar_page accessed remotely");
167 
168 	return NULL;
169 }
170 #else
171 static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
172 {
173 	return NULL;
174 }
175 #endif
176 
177 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
178 			     struct vm_area_struct *vma, struct vm_fault *vmf)
179 {
180 	struct page *timens_page = find_timens_vvar_page(vma);
181 	unsigned long pfn;
182 
183 	switch (vmf->pgoff) {
184 	case VVAR_DATA_PAGE_OFFSET:
185 		if (timens_page)
186 			pfn = page_to_pfn(timens_page);
187 		else
188 			pfn = sym_to_pfn(vdso_data);
189 		break;
190 #ifdef CONFIG_TIME_NS
191 	case VVAR_TIMENS_PAGE_OFFSET:
192 		/*
193 		 * If a task belongs to a time namespace then a namespace
194 		 * specific VVAR is mapped with the VVAR_DATA_PAGE_OFFSET and
195 		 * the real VVAR page is mapped with the VVAR_TIMENS_PAGE_OFFSET
196 		 * offset.
197 		 * See also the comment near timens_setup_vdso_data().
198 		 */
199 		if (!timens_page)
200 			return VM_FAULT_SIGBUS;
201 		pfn = sym_to_pfn(vdso_data);
202 		break;
203 #endif /* CONFIG_TIME_NS */
204 	default:
205 		return VM_FAULT_SIGBUS;
206 	}
207 
208 	return vmf_insert_pfn(vma, vmf->address, pfn);
209 }
210 
211 static int __setup_additional_pages(enum vdso_abi abi,
212 				    struct mm_struct *mm,
213 				    struct linux_binprm *bprm,
214 				    int uses_interp)
215 {
216 	unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
217 	unsigned long gp_flags = 0;
218 	void *ret;
219 
220 	BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);
221 
222 	vdso_text_len = vdso_info[abi].vdso_pages << PAGE_SHIFT;
223 	/* Be sure to map the data page */
224 	vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE;
225 
226 	vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
227 	if (IS_ERR_VALUE(vdso_base)) {
228 		ret = ERR_PTR(vdso_base);
229 		goto up_fail;
230 	}
231 
232 	ret = _install_special_mapping(mm, vdso_base, VVAR_NR_PAGES * PAGE_SIZE,
233 				       VM_READ|VM_MAYREAD|VM_PFNMAP,
234 				       vdso_info[abi].dm);
235 	if (IS_ERR(ret))
236 		goto up_fail;
237 
238 	if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && system_supports_bti())
239 		gp_flags = VM_ARM64_BTI;
240 
241 	vdso_base += VVAR_NR_PAGES * PAGE_SIZE;
242 	mm->context.vdso = (void *)vdso_base;
243 	ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
244 				       VM_READ|VM_EXEC|gp_flags|
245 				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
246 				       vdso_info[abi].cm);
247 	if (IS_ERR(ret))
248 		goto up_fail;
249 
250 	return 0;
251 
252 up_fail:
253 	mm->context.vdso = NULL;
254 	return PTR_ERR(ret);
255 }
256 
257 #ifdef CONFIG_COMPAT
258 /*
259  * Create and map the vectors page for AArch32 tasks.
260  */
261 enum aarch32_map {
262 	AA32_MAP_VECTORS, /* kuser helpers */
263 	AA32_MAP_SIGPAGE,
264 	AA32_MAP_VVAR,
265 	AA32_MAP_VDSO,
266 };
267 
268 static struct page *aarch32_vectors_page __ro_after_init;
269 static struct page *aarch32_sig_page __ro_after_init;
270 
271 static int aarch32_sigpage_mremap(const struct vm_special_mapping *sm,
272 				  struct vm_area_struct *new_vma)
273 {
274 	current->mm->context.sigpage = (void *)new_vma->vm_start;
275 
276 	return 0;
277 }
278 
279 static struct vm_special_mapping aarch32_vdso_maps[] = {
280 	[AA32_MAP_VECTORS] = {
281 		.name	= "[vectors]", /* ABI */
282 		.pages	= &aarch32_vectors_page,
283 	},
284 	[AA32_MAP_SIGPAGE] = {
285 		.name	= "[sigpage]", /* ABI */
286 		.pages	= &aarch32_sig_page,
287 		.mremap	= aarch32_sigpage_mremap,
288 	},
289 	[AA32_MAP_VVAR] = {
290 		.name = "[vvar]",
291 		.fault = vvar_fault,
292 	},
293 	[AA32_MAP_VDSO] = {
294 		.name = "[vdso]",
295 		.mremap = vdso_mremap,
296 	},
297 };
298 
299 static int aarch32_alloc_kuser_vdso_page(void)
300 {
301 	extern char __kuser_helper_start[], __kuser_helper_end[];
302 	int kuser_sz = __kuser_helper_end - __kuser_helper_start;
303 	unsigned long vdso_page;
304 
305 	if (!IS_ENABLED(CONFIG_KUSER_HELPERS))
306 		return 0;
307 
308 	vdso_page = get_zeroed_page(GFP_KERNEL);
309 	if (!vdso_page)
310 		return -ENOMEM;
311 
312 	memcpy((void *)(vdso_page + 0x1000 - kuser_sz), __kuser_helper_start,
313 	       kuser_sz);
314 	aarch32_vectors_page = virt_to_page(vdso_page);
315 	return 0;
316 }
317 
318 #define COMPAT_SIGPAGE_POISON_WORD	0xe7fddef1
319 static int aarch32_alloc_sigpage(void)
320 {
321 	extern char __aarch32_sigret_code_start[], __aarch32_sigret_code_end[];
322 	int sigret_sz = __aarch32_sigret_code_end - __aarch32_sigret_code_start;
323 	__le32 poison = cpu_to_le32(COMPAT_SIGPAGE_POISON_WORD);
324 	void *sigpage;
325 
326 	sigpage = (void *)__get_free_page(GFP_KERNEL);
327 	if (!sigpage)
328 		return -ENOMEM;
329 
330 	memset32(sigpage, (__force u32)poison, PAGE_SIZE / sizeof(poison));
331 	memcpy(sigpage, __aarch32_sigret_code_start, sigret_sz);
332 	aarch32_sig_page = virt_to_page(sigpage);
333 	return 0;
334 }
335 
336 static int __init __aarch32_alloc_vdso_pages(void)
337 {
338 
339 	if (!IS_ENABLED(CONFIG_COMPAT_VDSO))
340 		return 0;
341 
342 	vdso_info[VDSO_ABI_AA32].dm = &aarch32_vdso_maps[AA32_MAP_VVAR];
343 	vdso_info[VDSO_ABI_AA32].cm = &aarch32_vdso_maps[AA32_MAP_VDSO];
344 
345 	return __vdso_init(VDSO_ABI_AA32);
346 }
347 
348 static int __init aarch32_alloc_vdso_pages(void)
349 {
350 	int ret;
351 
352 	ret = __aarch32_alloc_vdso_pages();
353 	if (ret)
354 		return ret;
355 
356 	ret = aarch32_alloc_sigpage();
357 	if (ret)
358 		return ret;
359 
360 	return aarch32_alloc_kuser_vdso_page();
361 }
362 arch_initcall(aarch32_alloc_vdso_pages);
363 
364 static int aarch32_kuser_helpers_setup(struct mm_struct *mm)
365 {
366 	void *ret;
367 
368 	if (!IS_ENABLED(CONFIG_KUSER_HELPERS))
369 		return 0;
370 
371 	/*
372 	 * Avoid VM_MAYWRITE for compatibility with arch/arm/, where it's
373 	 * not safe to CoW the page containing the CPU exception vectors.
374 	 */
375 	ret = _install_special_mapping(mm, AARCH32_VECTORS_BASE, PAGE_SIZE,
376 				       VM_READ | VM_EXEC |
377 				       VM_MAYREAD | VM_MAYEXEC,
378 				       &aarch32_vdso_maps[AA32_MAP_VECTORS]);
379 
380 	return PTR_ERR_OR_ZERO(ret);
381 }
382 
383 static int aarch32_sigreturn_setup(struct mm_struct *mm)
384 {
385 	unsigned long addr;
386 	void *ret;
387 
388 	addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
389 	if (IS_ERR_VALUE(addr)) {
390 		ret = ERR_PTR(addr);
391 		goto out;
392 	}
393 
394 	/*
395 	 * VM_MAYWRITE is required to allow gdb to Copy-on-Write and
396 	 * set breakpoints.
397 	 */
398 	ret = _install_special_mapping(mm, addr, PAGE_SIZE,
399 				       VM_READ | VM_EXEC | VM_MAYREAD |
400 				       VM_MAYWRITE | VM_MAYEXEC,
401 				       &aarch32_vdso_maps[AA32_MAP_SIGPAGE]);
402 	if (IS_ERR(ret))
403 		goto out;
404 
405 	mm->context.sigpage = (void *)addr;
406 
407 out:
408 	return PTR_ERR_OR_ZERO(ret);
409 }
410 
411 int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
412 {
413 	struct mm_struct *mm = current->mm;
414 	int ret;
415 
416 	if (mmap_write_lock_killable(mm))
417 		return -EINTR;
418 
419 	ret = aarch32_kuser_helpers_setup(mm);
420 	if (ret)
421 		goto out;
422 
423 	if (IS_ENABLED(CONFIG_COMPAT_VDSO)) {
424 		ret = __setup_additional_pages(VDSO_ABI_AA32, mm, bprm,
425 					       uses_interp);
426 		if (ret)
427 			goto out;
428 	}
429 
430 	ret = aarch32_sigreturn_setup(mm);
431 out:
432 	mmap_write_unlock(mm);
433 	return ret;
434 }
435 #endif /* CONFIG_COMPAT */
436 
437 enum aarch64_map {
438 	AA64_MAP_VVAR,
439 	AA64_MAP_VDSO,
440 };
441 
442 static struct vm_special_mapping aarch64_vdso_maps[] __ro_after_init = {
443 	[AA64_MAP_VVAR] = {
444 		.name	= "[vvar]",
445 		.fault = vvar_fault,
446 	},
447 	[AA64_MAP_VDSO] = {
448 		.name	= "[vdso]",
449 		.mremap = vdso_mremap,
450 	},
451 };
452 
453 static int __init vdso_init(void)
454 {
455 	vdso_info[VDSO_ABI_AA64].dm = &aarch64_vdso_maps[AA64_MAP_VVAR];
456 	vdso_info[VDSO_ABI_AA64].cm = &aarch64_vdso_maps[AA64_MAP_VDSO];
457 
458 	return __vdso_init(VDSO_ABI_AA64);
459 }
460 arch_initcall(vdso_init);
461 
462 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
463 {
464 	struct mm_struct *mm = current->mm;
465 	int ret;
466 
467 	if (mmap_write_lock_killable(mm))
468 		return -EINTR;
469 
470 	ret = __setup_additional_pages(VDSO_ABI_AA64, mm, bprm, uses_interp);
471 	mmap_write_unlock(mm);
472 
473 	return ret;
474 }
475