1 // SPDX-License-Identifier: GPL-2.0-only
3 * Copyright (C) 2020 ARM Ltd.
6 #include <linux/bitops.h>
7 #include <linux/kernel.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>
19 #include <asm/barrier.h>
20 #include <asm/cpufeature.h>
22 #include <asm/ptrace.h>
23 #include <asm/sysreg.h>
25 u64 gcr_kernel_excl __ro_after_init;
27 static bool report_fault_once = true;
29 #ifdef CONFIG_KASAN_HW_TAGS
30 /* Whether the MTE asynchronous mode is enabled. */
31 DEFINE_STATIC_KEY_FALSE(mte_async_mode);
32 EXPORT_SYMBOL_GPL(mte_async_mode);
35 static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
37 pte_t old_pte = READ_ONCE(*ptep);
39 if (check_swap && is_swap_pte(old_pte)) {
40 swp_entry_t entry = pte_to_swp_entry(old_pte);
42 if (!non_swap_entry(entry) && mte_restore_tags(entry, page))
46 page_kasan_tag_reset(page);
48 * We need smp_wmb() in between setting the flags and clearing the
49 * tags because if another thread reads page->flags and builds a
50 * tagged address out of it, there is an actual dependency to the
51 * memory access, but on the current thread we do not guarantee that
52 * the new page->flags are visible before the tags were updated.
55 mte_clear_page_tags(page_address(page));
58 void mte_sync_tags(pte_t *ptep, pte_t pte)
60 struct page *page = pte_page(pte);
61 long i, nr_pages = compound_nr(page);
62 bool check_swap = nr_pages == 1;
64 /* if PG_mte_tagged is set, tags have already been initialised */
65 for (i = 0; i < nr_pages; i++, page++) {
66 if (!test_and_set_bit(PG_mte_tagged, &page->flags))
67 mte_sync_page_tags(page, ptep, check_swap);
71 int memcmp_pages(struct page *page1, struct page *page2)
76 addr1 = page_address(page1);
77 addr2 = page_address(page2);
78 ret = memcmp(addr1, addr2, PAGE_SIZE);
80 if (!system_supports_mte() || ret)
84 * If the page content is identical but at least one of the pages is
85 * tagged, return non-zero to avoid KSM merging. If only one of the
86 * pages is tagged, set_pte_at() may zero or change the tags of the
87 * other page via mte_sync_tags().
89 if (test_bit(PG_mte_tagged, &page1->flags) ||
90 test_bit(PG_mte_tagged, &page2->flags))
91 return addr1 != addr2;
96 void mte_init_tags(u64 max_tag)
98 static bool gcr_kernel_excl_initialized;
100 if (!gcr_kernel_excl_initialized) {
102 * The format of the tags in KASAN is 0xFF and in MTE is 0xF.
103 * This conversion extracts an MTE tag from a KASAN tag.
105 u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
108 gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
109 gcr_kernel_excl_initialized = true;
112 /* Enable the kernel exclude mask for random tags generation. */
113 write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
116 static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
118 /* Enable MTE Sync Mode for EL1. */
119 sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
122 pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
125 #ifdef CONFIG_KASAN_HW_TAGS
126 void mte_enable_kernel_sync(void)
129 * Make sure we enter this function when no PE has set
130 * async mode previously.
132 WARN_ONCE(system_uses_mte_async_mode(),
133 "MTE async mode enabled system wide!");
135 __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
138 void mte_enable_kernel_async(void)
140 __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
143 * MTE async mode is set system wide by the first PE that
144 * executes this function.
146 * Note: If in future KASAN acquires a runtime switching
147 * mode in between sync and async, this strategy needs
150 if (!system_uses_mte_async_mode())
151 static_branch_enable(&mte_async_mode);
155 void mte_set_report_once(bool state)
157 WRITE_ONCE(report_fault_once, state);
160 bool mte_report_once(void)
162 return READ_ONCE(report_fault_once);
165 static void update_sctlr_el1_tcf0(u64 tcf0)
167 /* ISB required for the kernel uaccess routines */
168 sysreg_clear_set(sctlr_el1, SCTLR_EL1_TCF0_MASK, tcf0);
172 static void set_sctlr_el1_tcf0(u64 tcf0)
175 * mte_thread_switch() checks current->thread.sctlr_tcf0 as an
176 * optimisation. Disable preemption so that it does not see
177 * the variable update before the SCTLR_EL1.TCF0 one.
180 current->thread.sctlr_tcf0 = tcf0;
181 update_sctlr_el1_tcf0(tcf0);
185 static void update_gcr_el1_excl(u64 excl)
189 * Note that the mask controlled by the user via prctl() is an
190 * include while GCR_EL1 accepts an exclude mask.
191 * No need for ISB since this only affects EL0 currently, implicit
194 sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, excl);
197 static void set_gcr_el1_excl(u64 excl)
199 current->thread.gcr_user_excl = excl;
202 * SYS_GCR_EL1 will be set to current->thread.gcr_user_excl value
203 * by mte_set_user_gcr() in kernel_exit,
207 void flush_mte_state(void)
209 if (!system_supports_mte())
212 /* clear any pending asynchronous tag fault */
214 write_sysreg_s(0, SYS_TFSRE0_EL1);
215 clear_thread_flag(TIF_MTE_ASYNC_FAULT);
216 /* disable tag checking */
217 set_sctlr_el1_tcf0(SCTLR_EL1_TCF0_NONE);
218 /* reset tag generation mask */
219 set_gcr_el1_excl(SYS_GCR_EL1_EXCL_MASK);
222 void mte_thread_switch(struct task_struct *next)
224 if (!system_supports_mte())
227 /* avoid expensive SCTLR_EL1 accesses if no change */
228 if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
229 update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
232 void mte_suspend_exit(void)
234 if (!system_supports_mte())
237 update_gcr_el1_excl(gcr_kernel_excl);
240 long set_mte_ctrl(struct task_struct *task, unsigned long arg)
243 u64 gcr_excl = ~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
244 SYS_GCR_EL1_EXCL_MASK;
246 if (!system_supports_mte())
249 switch (arg & PR_MTE_TCF_MASK) {
250 case PR_MTE_TCF_NONE:
251 tcf0 = SCTLR_EL1_TCF0_NONE;
253 case PR_MTE_TCF_SYNC:
254 tcf0 = SCTLR_EL1_TCF0_SYNC;
256 case PR_MTE_TCF_ASYNC:
257 tcf0 = SCTLR_EL1_TCF0_ASYNC;
263 if (task != current) {
264 task->thread.sctlr_tcf0 = tcf0;
265 task->thread.gcr_user_excl = gcr_excl;
267 set_sctlr_el1_tcf0(tcf0);
268 set_gcr_el1_excl(gcr_excl);
274 long get_mte_ctrl(struct task_struct *task)
277 u64 incl = ~task->thread.gcr_user_excl & SYS_GCR_EL1_EXCL_MASK;
279 if (!system_supports_mte())
282 ret = incl << PR_MTE_TAG_SHIFT;
284 switch (task->thread.sctlr_tcf0) {
285 case SCTLR_EL1_TCF0_NONE:
286 ret |= PR_MTE_TCF_NONE;
288 case SCTLR_EL1_TCF0_SYNC:
289 ret |= PR_MTE_TCF_SYNC;
291 case SCTLR_EL1_TCF0_ASYNC:
292 ret |= PR_MTE_TCF_ASYNC;
300 * Access MTE tags in another process' address space as given in mm. Update
301 * the number of tags copied. Return 0 if any tags copied, error otherwise.
302 * Inspired by __access_remote_vm().
304 static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
305 struct iovec *kiov, unsigned int gup_flags)
307 struct vm_area_struct *vma;
308 void __user *buf = kiov->iov_base;
309 size_t len = kiov->iov_len;
311 int write = gup_flags & FOLL_WRITE;
313 if (!access_ok(buf, len))
316 if (mmap_read_lock_killable(mm))
320 unsigned long tags, offset;
322 struct page *page = NULL;
324 ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
330 * Only copy tags if the page has been mapped as PROT_MTE
331 * (PG_mte_tagged set). Otherwise the tags are not valid and
332 * not accessible to user. Moreover, an mprotect(PROT_MTE)
333 * would cause the existing tags to be cleared if the page
334 * was never mapped with PROT_MTE.
336 if (!(vma->vm_flags & VM_MTE)) {
341 WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags));
343 /* limit access to the end of the page */
344 offset = offset_in_page(addr);
345 tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE);
347 maddr = page_address(page);
349 tags = mte_copy_tags_from_user(maddr + offset, buf, tags);
350 set_page_dirty_lock(page);
352 tags = mte_copy_tags_to_user(buf, maddr + offset, tags);
356 /* error accessing the tracer's buffer */
362 addr += tags * MTE_GRANULE_SIZE;
364 mmap_read_unlock(mm);
366 /* return an error if no tags copied */
367 kiov->iov_len = buf - kiov->iov_base;
368 if (!kiov->iov_len) {
369 /* check for error accessing the tracee's address space */
380 * Copy MTE tags in another process' address space at 'addr' to/from tracer's
381 * iovec buffer. Return 0 on success. Inspired by ptrace_access_vm().
383 static int access_remote_tags(struct task_struct *tsk, unsigned long addr,
384 struct iovec *kiov, unsigned int gup_flags)
386 struct mm_struct *mm;
389 mm = get_task_mm(tsk);
393 if (!tsk->ptrace || (current != tsk->parent) ||
394 ((get_dumpable(mm) != SUID_DUMP_USER) &&
395 !ptracer_capable(tsk, mm->user_ns))) {
400 ret = __access_remote_tags(mm, addr, kiov, gup_flags);
406 int mte_ptrace_copy_tags(struct task_struct *child, long request,
407 unsigned long addr, unsigned long data)
411 struct iovec __user *uiov = (void __user *)data;
412 unsigned int gup_flags = FOLL_FORCE;
414 if (!system_supports_mte())
417 if (get_user(kiov.iov_base, &uiov->iov_base) ||
418 get_user(kiov.iov_len, &uiov->iov_len))
421 if (request == PTRACE_POKEMTETAGS)
422 gup_flags |= FOLL_WRITE;
424 /* align addr to the MTE tag granule */
425 addr &= MTE_GRANULE_MASK;
427 ret = access_remote_tags(child, addr, &kiov, gup_flags);
429 ret = put_user(kiov.iov_len, &uiov->iov_len);