xref: /openbmc/linux/arch/arm64/kernel/mte.c (revision 0b26ca68) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2020 ARM Ltd.
4  */
5 
6 #include <linux/bitops.h>
7 #include <linux/kernel.h>
8 #include <linux/mm.h>
9 #include <linux/prctl.h>
10 #include <linux/sched.h>
11 #include <linux/sched/mm.h>
12 #include <linux/string.h>
13 #include <linux/swap.h>
14 #include <linux/swapops.h>
15 #include <linux/thread_info.h>
16 #include <linux/types.h>
17 #include <linux/uio.h>
18 
19 #include <asm/barrier.h>
20 #include <asm/cpufeature.h>
21 #include <asm/mte.h>
22 #include <asm/mte-kasan.h>
23 #include <asm/ptrace.h>
24 #include <asm/sysreg.h>
25 
26 u64 gcr_kernel_excl __ro_after_init;
27 
28 static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
29 {
30 	pte_t old_pte = READ_ONCE(*ptep);
31 
32 	if (check_swap && is_swap_pte(old_pte)) {
33 		swp_entry_t entry = pte_to_swp_entry(old_pte);
34 
35 		if (!non_swap_entry(entry) && mte_restore_tags(entry, page))
36 			return;
37 	}
38 
39 	page_kasan_tag_reset(page);
40 	/*
41 	 * We need smp_wmb() in between setting the flags and clearing the
42 	 * tags because if another thread reads page->flags and builds a
43 	 * tagged address out of it, there is an actual dependency to the
44 	 * memory access, but on the current thread we do not guarantee that
45 	 * the new page->flags are visible before the tags were updated.
46 	 */
47 	smp_wmb();
48 	mte_clear_page_tags(page_address(page));
49 }
50 
51 void mte_sync_tags(pte_t *ptep, pte_t pte)
52 {
53 	struct page *page = pte_page(pte);
54 	long i, nr_pages = compound_nr(page);
55 	bool check_swap = nr_pages == 1;
56 
57 	/* if PG_mte_tagged is set, tags have already been initialised */
58 	for (i = 0; i < nr_pages; i++, page++) {
59 		if (!test_and_set_bit(PG_mte_tagged, &page->flags))
60 			mte_sync_page_tags(page, ptep, check_swap);
61 	}
62 }
63 
64 int memcmp_pages(struct page *page1, struct page *page2)
65 {
66 	char *addr1, *addr2;
67 	int ret;
68 
69 	addr1 = page_address(page1);
70 	addr2 = page_address(page2);
71 	ret = memcmp(addr1, addr2, PAGE_SIZE);
72 
73 	if (!system_supports_mte() || ret)
74 		return ret;
75 
76 	/*
77 	 * If the page content is identical but at least one of the pages is
78 	 * tagged, return non-zero to avoid KSM merging. If only one of the
79 	 * pages is tagged, set_pte_at() may zero or change the tags of the
80 	 * other page via mte_sync_tags().
81 	 */
82 	if (test_bit(PG_mte_tagged, &page1->flags) ||
83 	    test_bit(PG_mte_tagged, &page2->flags))
84 		return addr1 != addr2;
85 
86 	return ret;
87 }
88 
89 u8 mte_get_mem_tag(void *addr)
90 {
91 	if (!system_supports_mte())
92 		return 0xFF;
93 
94 	asm(__MTE_PREAMBLE "ldg %0, [%0]"
95 	    : "+r" (addr));
96 
97 	return mte_get_ptr_tag(addr);
98 }
99 
100 u8 mte_get_random_tag(void)
101 {
102 	void *addr;
103 
104 	if (!system_supports_mte())
105 		return 0xFF;
106 
107 	asm(__MTE_PREAMBLE "irg %0, %0"
108 	    : "+r" (addr));
109 
110 	return mte_get_ptr_tag(addr);
111 }
112 
113 void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
114 {
115 	void *ptr = addr;
116 
117 	if ((!system_supports_mte()) || (size == 0))
118 		return addr;
119 
120 	/* Make sure that size is MTE granule aligned. */
121 	WARN_ON(size & (MTE_GRANULE_SIZE - 1));
122 
123 	/* Make sure that the address is MTE granule aligned. */
124 	WARN_ON((u64)addr & (MTE_GRANULE_SIZE - 1));
125 
126 	tag = 0xF0 | tag;
127 	ptr = (void *)__tag_set(ptr, tag);
128 
129 	mte_assign_mem_tag_range(ptr, size);
130 
131 	return ptr;
132 }
133 
134 void mte_init_tags(u64 max_tag)
135 {
136 	static bool gcr_kernel_excl_initialized;
137 
138 	if (!gcr_kernel_excl_initialized) {
139 		/*
140 		 * The format of the tags in KASAN is 0xFF and in MTE is 0xF.
141 		 * This conversion extracts an MTE tag from a KASAN tag.
142 		 */
143 		u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
144 					     max_tag), 0);
145 
146 		gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
147 		gcr_kernel_excl_initialized = true;
148 	}
149 
150 	/* Enable the kernel exclude mask for random tags generation. */
151 	write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
152 }
153 
154 void mte_enable_kernel(void)
155 {
156 	/* Enable MTE Sync Mode for EL1. */
157 	sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
158 	isb();
159 }
160 
161 static void update_sctlr_el1_tcf0(u64 tcf0)
162 {
163 	/* ISB required for the kernel uaccess routines */
164 	sysreg_clear_set(sctlr_el1, SCTLR_EL1_TCF0_MASK, tcf0);
165 	isb();
166 }
167 
168 static void set_sctlr_el1_tcf0(u64 tcf0)
169 {
170 	/*
171 	 * mte_thread_switch() checks current->thread.sctlr_tcf0 as an
172 	 * optimisation. Disable preemption so that it does not see
173 	 * the variable update before the SCTLR_EL1.TCF0 one.
174 	 */
175 	preempt_disable();
176 	current->thread.sctlr_tcf0 = tcf0;
177 	update_sctlr_el1_tcf0(tcf0);
178 	preempt_enable();
179 }
180 
181 static void update_gcr_el1_excl(u64 excl)
182 {
183 
184 	/*
185 	 * Note that the mask controlled by the user via prctl() is an
186 	 * include while GCR_EL1 accepts an exclude mask.
187 	 * No need for ISB since this only affects EL0 currently, implicit
188 	 * with ERET.
189 	 */
190 	sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, excl);
191 }
192 
193 static void set_gcr_el1_excl(u64 excl)
194 {
195 	current->thread.gcr_user_excl = excl;
196 
197 	/*
198 	 * SYS_GCR_EL1 will be set to current->thread.gcr_user_excl value
199 	 * by mte_set_user_gcr() in kernel_exit,
200 	 */
201 }
202 
203 void flush_mte_state(void)
204 {
205 	if (!system_supports_mte())
206 		return;
207 
208 	/* clear any pending asynchronous tag fault */
209 	dsb(ish);
210 	write_sysreg_s(0, SYS_TFSRE0_EL1);
211 	clear_thread_flag(TIF_MTE_ASYNC_FAULT);
212 	/* disable tag checking */
213 	set_sctlr_el1_tcf0(SCTLR_EL1_TCF0_NONE);
214 	/* reset tag generation mask */
215 	set_gcr_el1_excl(SYS_GCR_EL1_EXCL_MASK);
216 }
217 
218 void mte_thread_switch(struct task_struct *next)
219 {
220 	if (!system_supports_mte())
221 		return;
222 
223 	/* avoid expensive SCTLR_EL1 accesses if no change */
224 	if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
225 		update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
226 }
227 
228 void mte_suspend_exit(void)
229 {
230 	if (!system_supports_mte())
231 		return;
232 
233 	update_gcr_el1_excl(gcr_kernel_excl);
234 }
235 
236 long set_mte_ctrl(struct task_struct *task, unsigned long arg)
237 {
238 	u64 tcf0;
239 	u64 gcr_excl = ~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
240 		       SYS_GCR_EL1_EXCL_MASK;
241 
242 	if (!system_supports_mte())
243 		return 0;
244 
245 	switch (arg & PR_MTE_TCF_MASK) {
246 	case PR_MTE_TCF_NONE:
247 		tcf0 = SCTLR_EL1_TCF0_NONE;
248 		break;
249 	case PR_MTE_TCF_SYNC:
250 		tcf0 = SCTLR_EL1_TCF0_SYNC;
251 		break;
252 	case PR_MTE_TCF_ASYNC:
253 		tcf0 = SCTLR_EL1_TCF0_ASYNC;
254 		break;
255 	default:
256 		return -EINVAL;
257 	}
258 
259 	if (task != current) {
260 		task->thread.sctlr_tcf0 = tcf0;
261 		task->thread.gcr_user_excl = gcr_excl;
262 	} else {
263 		set_sctlr_el1_tcf0(tcf0);
264 		set_gcr_el1_excl(gcr_excl);
265 	}
266 
267 	return 0;
268 }
269 
270 long get_mte_ctrl(struct task_struct *task)
271 {
272 	unsigned long ret;
273 	u64 incl = ~task->thread.gcr_user_excl & SYS_GCR_EL1_EXCL_MASK;
274 
275 	if (!system_supports_mte())
276 		return 0;
277 
278 	ret = incl << PR_MTE_TAG_SHIFT;
279 
280 	switch (task->thread.sctlr_tcf0) {
281 	case SCTLR_EL1_TCF0_NONE:
282 		ret |= PR_MTE_TCF_NONE;
283 		break;
284 	case SCTLR_EL1_TCF0_SYNC:
285 		ret |= PR_MTE_TCF_SYNC;
286 		break;
287 	case SCTLR_EL1_TCF0_ASYNC:
288 		ret |= PR_MTE_TCF_ASYNC;
289 		break;
290 	}
291 
292 	return ret;
293 }
294 
295 /*
296  * Access MTE tags in another process' address space as given in mm. Update
297  * the number of tags copied. Return 0 if any tags copied, error otherwise.
298  * Inspired by __access_remote_vm().
299  */
300 static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
301 				struct iovec *kiov, unsigned int gup_flags)
302 {
303 	struct vm_area_struct *vma;
304 	void __user *buf = kiov->iov_base;
305 	size_t len = kiov->iov_len;
306 	int ret;
307 	int write = gup_flags & FOLL_WRITE;
308 
309 	if (!access_ok(buf, len))
310 		return -EFAULT;
311 
312 	if (mmap_read_lock_killable(mm))
313 		return -EIO;
314 
315 	while (len) {
316 		unsigned long tags, offset;
317 		void *maddr;
318 		struct page *page = NULL;
319 
320 		ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
321 					    &vma, NULL);
322 		if (ret <= 0)
323 			break;
324 
325 		/*
326 		 * Only copy tags if the page has been mapped as PROT_MTE
327 		 * (PG_mte_tagged set). Otherwise the tags are not valid and
328 		 * not accessible to user. Moreover, an mprotect(PROT_MTE)
329 		 * would cause the existing tags to be cleared if the page
330 		 * was never mapped with PROT_MTE.
331 		 */
332 		if (!test_bit(PG_mte_tagged, &page->flags)) {
333 			ret = -EOPNOTSUPP;
334 			put_page(page);
335 			break;
336 		}
337 
338 		/* limit access to the end of the page */
339 		offset = offset_in_page(addr);
340 		tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE);
341 
342 		maddr = page_address(page);
343 		if (write) {
344 			tags = mte_copy_tags_from_user(maddr + offset, buf, tags);
345 			set_page_dirty_lock(page);
346 		} else {
347 			tags = mte_copy_tags_to_user(buf, maddr + offset, tags);
348 		}
349 		put_page(page);
350 
351 		/* error accessing the tracer's buffer */
352 		if (!tags)
353 			break;
354 
355 		len -= tags;
356 		buf += tags;
357 		addr += tags * MTE_GRANULE_SIZE;
358 	}
359 	mmap_read_unlock(mm);
360 
361 	/* return an error if no tags copied */
362 	kiov->iov_len = buf - kiov->iov_base;
363 	if (!kiov->iov_len) {
364 		/* check for error accessing the tracee's address space */
365 		if (ret <= 0)
366 			return -EIO;
367 		else
368 			return -EFAULT;
369 	}
370 
371 	return 0;
372 }
373 
374 /*
375  * Copy MTE tags in another process' address space at 'addr' to/from tracer's
376  * iovec buffer. Return 0 on success. Inspired by ptrace_access_vm().
377  */
378 static int access_remote_tags(struct task_struct *tsk, unsigned long addr,
379 			      struct iovec *kiov, unsigned int gup_flags)
380 {
381 	struct mm_struct *mm;
382 	int ret;
383 
384 	mm = get_task_mm(tsk);
385 	if (!mm)
386 		return -EPERM;
387 
388 	if (!tsk->ptrace || (current != tsk->parent) ||
389 	    ((get_dumpable(mm) != SUID_DUMP_USER) &&
390 	     !ptracer_capable(tsk, mm->user_ns))) {
391 		mmput(mm);
392 		return -EPERM;
393 	}
394 
395 	ret = __access_remote_tags(mm, addr, kiov, gup_flags);
396 	mmput(mm);
397 
398 	return ret;
399 }
400 
401 int mte_ptrace_copy_tags(struct task_struct *child, long request,
402 			 unsigned long addr, unsigned long data)
403 {
404 	int ret;
405 	struct iovec kiov;
406 	struct iovec __user *uiov = (void __user *)data;
407 	unsigned int gup_flags = FOLL_FORCE;
408 
409 	if (!system_supports_mte())
410 		return -EIO;
411 
412 	if (get_user(kiov.iov_base, &uiov->iov_base) ||
413 	    get_user(kiov.iov_len, &uiov->iov_len))
414 		return -EFAULT;
415 
416 	if (request == PTRACE_POKEMTETAGS)
417 		gup_flags |= FOLL_WRITE;
418 
419 	/* align addr to the MTE tag granule */
420 	addr &= MTE_GRANULE_MASK;
421 
422 	ret = access_remote_tags(child, addr, &kiov, gup_flags);
423 	if (!ret)
424 		ret = put_user(kiov.iov_len, &uiov->iov_len);
425 
426 	return ret;
427 }
428