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/cpu.h> 8 #include <linux/kernel.h> 9 #include <linux/mm.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> 19 20 #include <asm/barrier.h> 21 #include <asm/cpufeature.h> 22 #include <asm/mte.h> 23 #include <asm/ptrace.h> 24 #include <asm/sysreg.h> 25 26 static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred); 27 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); 32 #endif 33 34 static void mte_sync_page_tags(struct page *page, pte_t old_pte, 35 bool check_swap, bool pte_is_tagged) 36 { 37 if (check_swap && is_swap_pte(old_pte)) { 38 swp_entry_t entry = pte_to_swp_entry(old_pte); 39 40 if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) 41 return; 42 } 43 44 if (!pte_is_tagged) 45 return; 46 47 page_kasan_tag_reset(page); 48 /* 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. 54 */ 55 smp_wmb(); 56 mte_clear_page_tags(page_address(page)); 57 } 58 59 void mte_sync_tags(pte_t old_pte, pte_t pte) 60 { 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); 65 66 /* Early out if there's nothing to do */ 67 if (!check_swap && !pte_is_tagged) 68 return; 69 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, 74 pte_is_tagged); 75 } 76 } 77 78 int memcmp_pages(struct page *page1, struct page *page2) 79 { 80 char *addr1, *addr2; 81 int ret; 82 83 addr1 = page_address(page1); 84 addr2 = page_address(page2); 85 ret = memcmp(addr1, addr2, PAGE_SIZE); 86 87 if (!system_supports_mte() || ret) 88 return ret; 89 90 /* 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(). 95 */ 96 if (test_bit(PG_mte_tagged, &page1->flags) || 97 test_bit(PG_mte_tagged, &page2->flags)) 98 return addr1 != addr2; 99 100 return ret; 101 } 102 103 static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) 104 { 105 /* Enable MTE Sync Mode for EL1. */ 106 sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf); 107 isb(); 108 109 pr_info_once("MTE: enabled in %s mode at EL1\n", mode); 110 } 111 112 #ifdef CONFIG_KASAN_HW_TAGS 113 void mte_enable_kernel_sync(void) 114 { 115 /* 116 * Make sure we enter this function when no PE has set 117 * async mode previously. 118 */ 119 WARN_ONCE(system_uses_mte_async_mode(), 120 "MTE async mode enabled system wide!"); 121 122 __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC); 123 } 124 125 void mte_enable_kernel_async(void) 126 { 127 __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); 128 129 /* 130 * MTE async mode is set system wide by the first PE that 131 * executes this function. 132 * 133 * Note: If in future KASAN acquires a runtime switching 134 * mode in between sync and async, this strategy needs 135 * to be reviewed. 136 */ 137 if (!system_uses_mte_async_mode()) 138 static_branch_enable(&mte_async_mode); 139 } 140 #endif 141 142 #ifdef CONFIG_KASAN_HW_TAGS 143 void mte_check_tfsr_el1(void) 144 { 145 u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1); 146 147 if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) { 148 /* 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). 152 */ 153 write_sysreg_s(0, SYS_TFSR_EL1); 154 155 kasan_report_async(); 156 } 157 } 158 #endif 159 160 static void mte_update_sctlr_user(struct task_struct *task) 161 { 162 /* 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. 167 */ 168 unsigned long sctlr = task->thread.sctlr_user; 169 unsigned long mte_ctrl = task->thread.mte_ctrl; 170 unsigned long pref, resolved_mte_tcf; 171 172 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; 180 } 181 182 void mte_thread_init_user(void) 183 { 184 if (!system_supports_mte()) 185 return; 186 187 /* clear any pending asynchronous tag fault */ 188 dsb(ish); 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); 193 } 194 195 void mte_thread_switch(struct task_struct *next) 196 { 197 if (!system_supports_mte()) 198 return; 199 200 mte_update_sctlr_user(next); 201 202 /* 203 * Check if an async tag exception occurred at EL1. 204 * 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. 208 */ 209 isb(); 210 mte_check_tfsr_el1(); 211 } 212 213 void mte_suspend_enter(void) 214 { 215 if (!system_supports_mte()) 216 return; 217 218 /* 219 * The barriers are required to guarantee that the indirect writes 220 * to TFSR_EL1 are synchronized before we report the state. 221 */ 222 dsb(nsh); 223 isb(); 224 225 /* Report SYS_TFSR_EL1 before suspend entry */ 226 mte_check_tfsr_el1(); 227 } 228 229 long set_mte_ctrl(struct task_struct *task, unsigned long arg) 230 { 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; 233 234 if (!system_supports_mte()) 235 return 0; 236 237 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; 241 242 task->thread.mte_ctrl = mte_ctrl; 243 if (task == current) { 244 preempt_disable(); 245 mte_update_sctlr_user(task); 246 update_sctlr_el1(task->thread.sctlr_user); 247 preempt_enable(); 248 } 249 250 return 0; 251 } 252 253 long get_mte_ctrl(struct task_struct *task) 254 { 255 unsigned long ret; 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; 259 260 if (!system_supports_mte()) 261 return 0; 262 263 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; 268 269 return ret; 270 } 271 272 /* 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(). 276 */ 277 static int __access_remote_tags(struct mm_struct *mm, unsigned long addr, 278 struct iovec *kiov, unsigned int gup_flags) 279 { 280 struct vm_area_struct *vma; 281 void __user *buf = kiov->iov_base; 282 size_t len = kiov->iov_len; 283 int ret; 284 int write = gup_flags & FOLL_WRITE; 285 286 if (!access_ok(buf, len)) 287 return -EFAULT; 288 289 if (mmap_read_lock_killable(mm)) 290 return -EIO; 291 292 while (len) { 293 unsigned long tags, offset; 294 void *maddr; 295 struct page *page = NULL; 296 297 ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page, 298 &vma, NULL); 299 if (ret <= 0) 300 break; 301 302 /* 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. 308 */ 309 if (!(vma->vm_flags & VM_MTE)) { 310 ret = -EOPNOTSUPP; 311 put_page(page); 312 break; 313 } 314 WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags)); 315 316 /* limit access to the end of the page */ 317 offset = offset_in_page(addr); 318 tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE); 319 320 maddr = page_address(page); 321 if (write) { 322 tags = mte_copy_tags_from_user(maddr + offset, buf, tags); 323 set_page_dirty_lock(page); 324 } else { 325 tags = mte_copy_tags_to_user(buf, maddr + offset, tags); 326 } 327 put_page(page); 328 329 /* error accessing the tracer's buffer */ 330 if (!tags) 331 break; 332 333 len -= tags; 334 buf += tags; 335 addr += tags * MTE_GRANULE_SIZE; 336 } 337 mmap_read_unlock(mm); 338 339 /* 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 */ 343 if (ret <= 0) 344 return -EIO; 345 else 346 return -EFAULT; 347 } 348 349 return 0; 350 } 351 352 /* 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(). 355 */ 356 static int access_remote_tags(struct task_struct *tsk, unsigned long addr, 357 struct iovec *kiov, unsigned int gup_flags) 358 { 359 struct mm_struct *mm; 360 int ret; 361 362 mm = get_task_mm(tsk); 363 if (!mm) 364 return -EPERM; 365 366 if (!tsk->ptrace || (current != tsk->parent) || 367 ((get_dumpable(mm) != SUID_DUMP_USER) && 368 !ptracer_capable(tsk, mm->user_ns))) { 369 mmput(mm); 370 return -EPERM; 371 } 372 373 ret = __access_remote_tags(mm, addr, kiov, gup_flags); 374 mmput(mm); 375 376 return ret; 377 } 378 379 int mte_ptrace_copy_tags(struct task_struct *child, long request, 380 unsigned long addr, unsigned long data) 381 { 382 int ret; 383 struct iovec kiov; 384 struct iovec __user *uiov = (void __user *)data; 385 unsigned int gup_flags = FOLL_FORCE; 386 387 if (!system_supports_mte()) 388 return -EIO; 389 390 if (get_user(kiov.iov_base, &uiov->iov_base) || 391 get_user(kiov.iov_len, &uiov->iov_len)) 392 return -EFAULT; 393 394 if (request == PTRACE_POKEMTETAGS) 395 gup_flags |= FOLL_WRITE; 396 397 /* align addr to the MTE tag granule */ 398 addr &= MTE_GRANULE_MASK; 399 400 ret = access_remote_tags(child, addr, &kiov, gup_flags); 401 if (!ret) 402 ret = put_user(kiov.iov_len, &uiov->iov_len); 403 404 return ret; 405 } 406 407 static ssize_t mte_tcf_preferred_show(struct device *dev, 408 struct device_attribute *attr, char *buf) 409 { 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"); 415 default: 416 return sysfs_emit(buf, "???\n"); 417 } 418 } 419 420 static ssize_t mte_tcf_preferred_store(struct device *dev, 421 struct device_attribute *attr, 422 const char *buf, size_t count) 423 { 424 u64 tcf; 425 426 if (sysfs_streq(buf, "async")) 427 tcf = MTE_CTRL_TCF_ASYNC; 428 else if (sysfs_streq(buf, "sync")) 429 tcf = MTE_CTRL_TCF_SYNC; 430 else 431 return -EINVAL; 432 433 device_lock(dev); 434 per_cpu(mte_tcf_preferred, dev->id) = tcf; 435 device_unlock(dev); 436 437 return count; 438 } 439 static DEVICE_ATTR_RW(mte_tcf_preferred); 440 441 static int register_mte_tcf_preferred_sysctl(void) 442 { 443 unsigned int cpu; 444 445 if (!system_supports_mte()) 446 return 0; 447 448 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); 452 } 453 454 return 0; 455 } 456 subsys_initcall(register_mte_tcf_preferred_sysctl); 457