1 // SPDX-License-Identifier: GPL-2.0-only
3 * Copyright (C) 2020 ARM Ltd.
6 #include <linux/bitops.h>
8 #include <linux/kernel.h>
10 #include <linux/prctl.h>
11 #include <linux/sched.h>
12 #include <linux/sched/mm.h>
13 #include <linux/string.h>
14 #include <linux/swap.h>
15 #include <linux/swapops.h>
16 #include <linux/thread_info.h>
17 #include <linux/types.h>
18 #include <linux/uio.h>
20 #include <asm/barrier.h>
21 #include <asm/cpufeature.h>
23 #include <asm/ptrace.h>
24 #include <asm/sysreg.h>
26 static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);
28 #ifdef CONFIG_KASAN_HW_TAGS
29 /* Whether the MTE asynchronous mode is enabled. */
30 DEFINE_STATIC_KEY_FALSE(mte_async_mode);
31 EXPORT_SYMBOL_GPL(mte_async_mode);
34 static void mte_sync_page_tags(struct page *page, pte_t old_pte,
35 bool check_swap, bool pte_is_tagged)
37 if (check_swap && is_swap_pte(old_pte)) {
38 swp_entry_t entry = pte_to_swp_entry(old_pte);
40 if (!non_swap_entry(entry) && mte_restore_tags(entry, page))
47 page_kasan_tag_reset(page);
49 * We need smp_wmb() in between setting the flags and clearing the
50 * tags because if another thread reads page->flags and builds a
51 * tagged address out of it, there is an actual dependency to the
52 * memory access, but on the current thread we do not guarantee that
53 * the new page->flags are visible before the tags were updated.
56 mte_clear_page_tags(page_address(page));
59 void mte_sync_tags(pte_t old_pte, pte_t pte)
61 struct page *page = pte_page(pte);
62 long i, nr_pages = compound_nr(page);
63 bool check_swap = nr_pages == 1;
64 bool pte_is_tagged = pte_tagged(pte);
66 /* Early out if there's nothing to do */
67 if (!check_swap && !pte_is_tagged)
70 /* if PG_mte_tagged is set, tags have already been initialised */
71 for (i = 0; i < nr_pages; i++, page++) {
72 if (!test_and_set_bit(PG_mte_tagged, &page->flags))
73 mte_sync_page_tags(page, old_pte, check_swap,
78 int memcmp_pages(struct page *page1, struct page *page2)
83 addr1 = page_address(page1);
84 addr2 = page_address(page2);
85 ret = memcmp(addr1, addr2, PAGE_SIZE);
87 if (!system_supports_mte() || ret)
91 * If the page content is identical but at least one of the pages is
92 * tagged, return non-zero to avoid KSM merging. If only one of the
93 * pages is tagged, set_pte_at() may zero or change the tags of the
94 * other page via mte_sync_tags().
96 if (test_bit(PG_mte_tagged, &page1->flags) ||
97 test_bit(PG_mte_tagged, &page2->flags))
98 return addr1 != addr2;
103 static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
105 /* Enable MTE Sync Mode for EL1. */
106 sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
109 pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
112 #ifdef CONFIG_KASAN_HW_TAGS
113 void mte_enable_kernel_sync(void)
116 * Make sure we enter this function when no PE has set
117 * async mode previously.
119 WARN_ONCE(system_uses_mte_async_mode(),
120 "MTE async mode enabled system wide!");
122 __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
125 void mte_enable_kernel_async(void)
127 __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
130 * MTE async mode is set system wide by the first PE that
131 * executes this function.
133 * Note: If in future KASAN acquires a runtime switching
134 * mode in between sync and async, this strategy needs
137 if (!system_uses_mte_async_mode())
138 static_branch_enable(&mte_async_mode);
142 #ifdef CONFIG_KASAN_HW_TAGS
143 void mte_check_tfsr_el1(void)
145 u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
147 if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) {
149 * Note: isb() is not required after this direct write
150 * because there is no indirect read subsequent to it
151 * (per ARM DDI 0487F.c table D13-1).
153 write_sysreg_s(0, SYS_TFSR_EL1);
155 kasan_report_async();
160 static void mte_update_sctlr_user(struct task_struct *task)
163 * This must be called with preemption disabled and can only be called
164 * on the current or next task since the CPU must match where the thread
165 * is going to run. The caller is responsible for calling
166 * update_sctlr_el1() later in the same preemption disabled block.
168 unsigned long sctlr = task->thread.sctlr_user;
169 unsigned long mte_ctrl = task->thread.mte_ctrl;
170 unsigned long pref, resolved_mte_tcf;
172 pref = __this_cpu_read(mte_tcf_preferred);
173 resolved_mte_tcf = (mte_ctrl & pref) ? pref : mte_ctrl;
174 sctlr &= ~SCTLR_EL1_TCF0_MASK;
175 if (resolved_mte_tcf & MTE_CTRL_TCF_ASYNC)
176 sctlr |= SCTLR_EL1_TCF0_ASYNC;
177 else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC)
178 sctlr |= SCTLR_EL1_TCF0_SYNC;
179 task->thread.sctlr_user = sctlr;
182 void mte_thread_init_user(void)
184 if (!system_supports_mte())
187 /* clear any pending asynchronous tag fault */
189 write_sysreg_s(0, SYS_TFSRE0_EL1);
190 clear_thread_flag(TIF_MTE_ASYNC_FAULT);
191 /* disable tag checking and reset tag generation mask */
192 set_mte_ctrl(current, 0);
195 void mte_thread_switch(struct task_struct *next)
197 if (!system_supports_mte())
200 mte_update_sctlr_user(next);
203 * Check if an async tag exception occurred at EL1.
205 * Note: On the context switch path we rely on the dsb() present
206 * in __switch_to() to guarantee that the indirect writes to TFSR_EL1
207 * are synchronized before this point.
210 mte_check_tfsr_el1();
213 void mte_suspend_enter(void)
215 if (!system_supports_mte())
219 * The barriers are required to guarantee that the indirect writes
220 * to TFSR_EL1 are synchronized before we report the state.
225 /* Report SYS_TFSR_EL1 before suspend entry */
226 mte_check_tfsr_el1();
229 long set_mte_ctrl(struct task_struct *task, unsigned long arg)
231 u64 mte_ctrl = (~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
232 SYS_GCR_EL1_EXCL_MASK) << MTE_CTRL_GCR_USER_EXCL_SHIFT;
234 if (!system_supports_mte())
237 if (arg & PR_MTE_TCF_ASYNC)
238 mte_ctrl |= MTE_CTRL_TCF_ASYNC;
239 if (arg & PR_MTE_TCF_SYNC)
240 mte_ctrl |= MTE_CTRL_TCF_SYNC;
242 task->thread.mte_ctrl = mte_ctrl;
243 if (task == current) {
245 mte_update_sctlr_user(task);
246 update_sctlr_el1(task->thread.sctlr_user);
253 long get_mte_ctrl(struct task_struct *task)
256 u64 mte_ctrl = task->thread.mte_ctrl;
257 u64 incl = (~mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) &
258 SYS_GCR_EL1_EXCL_MASK;
260 if (!system_supports_mte())
263 ret = incl << PR_MTE_TAG_SHIFT;
264 if (mte_ctrl & MTE_CTRL_TCF_ASYNC)
265 ret |= PR_MTE_TCF_ASYNC;
266 if (mte_ctrl & MTE_CTRL_TCF_SYNC)
267 ret |= PR_MTE_TCF_SYNC;
273 * Access MTE tags in another process' address space as given in mm. Update
274 * the number of tags copied. Return 0 if any tags copied, error otherwise.
275 * Inspired by __access_remote_vm().
277 static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
278 struct iovec *kiov, unsigned int gup_flags)
280 struct vm_area_struct *vma;
281 void __user *buf = kiov->iov_base;
282 size_t len = kiov->iov_len;
284 int write = gup_flags & FOLL_WRITE;
286 if (!access_ok(buf, len))
289 if (mmap_read_lock_killable(mm))
293 unsigned long tags, offset;
295 struct page *page = NULL;
297 ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
303 * Only copy tags if the page has been mapped as PROT_MTE
304 * (PG_mte_tagged set). Otherwise the tags are not valid and
305 * not accessible to user. Moreover, an mprotect(PROT_MTE)
306 * would cause the existing tags to be cleared if the page
307 * was never mapped with PROT_MTE.
309 if (!(vma->vm_flags & VM_MTE)) {
314 WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags));
316 /* limit access to the end of the page */
317 offset = offset_in_page(addr);
318 tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE);
320 maddr = page_address(page);
322 tags = mte_copy_tags_from_user(maddr + offset, buf, tags);
323 set_page_dirty_lock(page);
325 tags = mte_copy_tags_to_user(buf, maddr + offset, tags);
329 /* error accessing the tracer's buffer */
335 addr += tags * MTE_GRANULE_SIZE;
337 mmap_read_unlock(mm);
339 /* return an error if no tags copied */
340 kiov->iov_len = buf - kiov->iov_base;
341 if (!kiov->iov_len) {
342 /* check for error accessing the tracee's address space */
353 * Copy MTE tags in another process' address space at 'addr' to/from tracer's
354 * iovec buffer. Return 0 on success. Inspired by ptrace_access_vm().
356 static int access_remote_tags(struct task_struct *tsk, unsigned long addr,
357 struct iovec *kiov, unsigned int gup_flags)
359 struct mm_struct *mm;
362 mm = get_task_mm(tsk);
366 if (!tsk->ptrace || (current != tsk->parent) ||
367 ((get_dumpable(mm) != SUID_DUMP_USER) &&
368 !ptracer_capable(tsk, mm->user_ns))) {
373 ret = __access_remote_tags(mm, addr, kiov, gup_flags);
379 int mte_ptrace_copy_tags(struct task_struct *child, long request,
380 unsigned long addr, unsigned long data)
384 struct iovec __user *uiov = (void __user *)data;
385 unsigned int gup_flags = FOLL_FORCE;
387 if (!system_supports_mte())
390 if (get_user(kiov.iov_base, &uiov->iov_base) ||
391 get_user(kiov.iov_len, &uiov->iov_len))
394 if (request == PTRACE_POKEMTETAGS)
395 gup_flags |= FOLL_WRITE;
397 /* align addr to the MTE tag granule */
398 addr &= MTE_GRANULE_MASK;
400 ret = access_remote_tags(child, addr, &kiov, gup_flags);
402 ret = put_user(kiov.iov_len, &uiov->iov_len);
407 static ssize_t mte_tcf_preferred_show(struct device *dev,
408 struct device_attribute *attr, char *buf)
410 switch (per_cpu(mte_tcf_preferred, dev->id)) {
411 case MTE_CTRL_TCF_ASYNC:
412 return sysfs_emit(buf, "async\n");
413 case MTE_CTRL_TCF_SYNC:
414 return sysfs_emit(buf, "sync\n");
416 return sysfs_emit(buf, "???\n");
420 static ssize_t mte_tcf_preferred_store(struct device *dev,
421 struct device_attribute *attr,
422 const char *buf, size_t count)
426 if (sysfs_streq(buf, "async"))
427 tcf = MTE_CTRL_TCF_ASYNC;
428 else if (sysfs_streq(buf, "sync"))
429 tcf = MTE_CTRL_TCF_SYNC;
434 per_cpu(mte_tcf_preferred, dev->id) = tcf;
439 static DEVICE_ATTR_RW(mte_tcf_preferred);
441 static int register_mte_tcf_preferred_sysctl(void)
445 if (!system_supports_mte())
448 for_each_possible_cpu(cpu) {
449 per_cpu(mte_tcf_preferred, cpu) = MTE_CTRL_TCF_ASYNC;
450 device_create_file(get_cpu_device(cpu),
451 &dev_attr_mte_tcf_preferred);
456 subsys_initcall(register_mte_tcf_preferred_sysctl);