1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com) 4 */ 5 6 #include <linux/mm.h> 7 #include <linux/sched/signal.h> 8 #include <linux/hardirq.h> 9 #include <linux/module.h> 10 #include <linux/uaccess.h> 11 #include <linux/sched/debug.h> 12 #include <asm/current.h> 13 #include <asm/pgtable.h> 14 #include <asm/tlbflush.h> 15 #include <arch.h> 16 #include <as-layout.h> 17 #include <kern_util.h> 18 #include <os.h> 19 #include <skas.h> 20 21 /* 22 * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by 23 * segv(). 24 */ 25 int handle_page_fault(unsigned long address, unsigned long ip, 26 int is_write, int is_user, int *code_out) 27 { 28 struct mm_struct *mm = current->mm; 29 struct vm_area_struct *vma; 30 pgd_t *pgd; 31 pud_t *pud; 32 pmd_t *pmd; 33 pte_t *pte; 34 int err = -EFAULT; 35 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 36 37 *code_out = SEGV_MAPERR; 38 39 /* 40 * If the fault was with pagefaults disabled, don't take the fault, just 41 * fail. 42 */ 43 if (faulthandler_disabled()) 44 goto out_nosemaphore; 45 46 if (is_user) 47 flags |= FAULT_FLAG_USER; 48 retry: 49 down_read(&mm->mmap_sem); 50 vma = find_vma(mm, address); 51 if (!vma) 52 goto out; 53 else if (vma->vm_start <= address) 54 goto good_area; 55 else if (!(vma->vm_flags & VM_GROWSDOWN)) 56 goto out; 57 else if (is_user && !ARCH_IS_STACKGROW(address)) 58 goto out; 59 else if (expand_stack(vma, address)) 60 goto out; 61 62 good_area: 63 *code_out = SEGV_ACCERR; 64 if (is_write) { 65 if (!(vma->vm_flags & VM_WRITE)) 66 goto out; 67 flags |= FAULT_FLAG_WRITE; 68 } else { 69 /* Don't require VM_READ|VM_EXEC for write faults! */ 70 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 71 goto out; 72 } 73 74 do { 75 vm_fault_t fault; 76 77 fault = handle_mm_fault(vma, address, flags); 78 79 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) 80 goto out_nosemaphore; 81 82 if (unlikely(fault & VM_FAULT_ERROR)) { 83 if (fault & VM_FAULT_OOM) { 84 goto out_of_memory; 85 } else if (fault & VM_FAULT_SIGSEGV) { 86 goto out; 87 } else if (fault & VM_FAULT_SIGBUS) { 88 err = -EACCES; 89 goto out; 90 } 91 BUG(); 92 } 93 if (flags & FAULT_FLAG_ALLOW_RETRY) { 94 if (fault & VM_FAULT_MAJOR) 95 current->maj_flt++; 96 else 97 current->min_flt++; 98 if (fault & VM_FAULT_RETRY) { 99 flags &= ~FAULT_FLAG_ALLOW_RETRY; 100 flags |= FAULT_FLAG_TRIED; 101 102 goto retry; 103 } 104 } 105 106 pgd = pgd_offset(mm, address); 107 pud = pud_offset(pgd, address); 108 pmd = pmd_offset(pud, address); 109 pte = pte_offset_kernel(pmd, address); 110 } while (!pte_present(*pte)); 111 err = 0; 112 /* 113 * The below warning was added in place of 114 * pte_mkyoung(); if (is_write) pte_mkdirty(); 115 * If it's triggered, we'd see normally a hang here (a clean pte is 116 * marked read-only to emulate the dirty bit). 117 * However, the generic code can mark a PTE writable but clean on a 118 * concurrent read fault, triggering this harmlessly. So comment it out. 119 */ 120 #if 0 121 WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte))); 122 #endif 123 flush_tlb_page(vma, address); 124 out: 125 up_read(&mm->mmap_sem); 126 out_nosemaphore: 127 return err; 128 129 out_of_memory: 130 /* 131 * We ran out of memory, call the OOM killer, and return the userspace 132 * (which will retry the fault, or kill us if we got oom-killed). 133 */ 134 up_read(&mm->mmap_sem); 135 if (!is_user) 136 goto out_nosemaphore; 137 pagefault_out_of_memory(); 138 return 0; 139 } 140 EXPORT_SYMBOL(handle_page_fault); 141 142 static void show_segv_info(struct uml_pt_regs *regs) 143 { 144 struct task_struct *tsk = current; 145 struct faultinfo *fi = UPT_FAULTINFO(regs); 146 147 if (!unhandled_signal(tsk, SIGSEGV)) 148 return; 149 150 if (!printk_ratelimit()) 151 return; 152 153 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x", 154 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, 155 tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi), 156 (void *)UPT_IP(regs), (void *)UPT_SP(regs), 157 fi->error_code); 158 159 print_vma_addr(KERN_CONT " in ", UPT_IP(regs)); 160 printk(KERN_CONT "\n"); 161 } 162 163 static void bad_segv(struct faultinfo fi, unsigned long ip) 164 { 165 current->thread.arch.faultinfo = fi; 166 force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi)); 167 } 168 169 void fatal_sigsegv(void) 170 { 171 force_sigsegv(SIGSEGV); 172 do_signal(¤t->thread.regs); 173 /* 174 * This is to tell gcc that we're not returning - do_signal 175 * can, in general, return, but in this case, it's not, since 176 * we just got a fatal SIGSEGV queued. 177 */ 178 os_dump_core(); 179 } 180 181 /** 182 * segv_handler() - the SIGSEGV handler 183 * @sig: the signal number 184 * @unused_si: the signal info struct; unused in this handler 185 * @regs: the ptrace register information 186 * 187 * The handler first extracts the faultinfo from the UML ptrace regs struct. 188 * If the userfault did not happen in an UML userspace process, bad_segv is called. 189 * Otherwise the signal did happen in a cloned userspace process, handle it. 190 */ 191 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) 192 { 193 struct faultinfo * fi = UPT_FAULTINFO(regs); 194 195 if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) { 196 show_segv_info(regs); 197 bad_segv(*fi, UPT_IP(regs)); 198 return; 199 } 200 segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs); 201 } 202 203 /* 204 * We give a *copy* of the faultinfo in the regs to segv. 205 * This must be done, since nesting SEGVs could overwrite 206 * the info in the regs. A pointer to the info then would 207 * give us bad data! 208 */ 209 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user, 210 struct uml_pt_regs *regs) 211 { 212 jmp_buf *catcher; 213 int si_code; 214 int err; 215 int is_write = FAULT_WRITE(fi); 216 unsigned long address = FAULT_ADDRESS(fi); 217 218 if (!is_user && regs) 219 current->thread.segv_regs = container_of(regs, struct pt_regs, regs); 220 221 if (!is_user && (address >= start_vm) && (address < end_vm)) { 222 flush_tlb_kernel_vm(); 223 goto out; 224 } 225 else if (current->mm == NULL) { 226 show_regs(container_of(regs, struct pt_regs, regs)); 227 panic("Segfault with no mm"); 228 } 229 else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) { 230 show_regs(container_of(regs, struct pt_regs, regs)); 231 panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx", 232 address, ip); 233 } 234 235 if (SEGV_IS_FIXABLE(&fi)) 236 err = handle_page_fault(address, ip, is_write, is_user, 237 &si_code); 238 else { 239 err = -EFAULT; 240 /* 241 * A thread accessed NULL, we get a fault, but CR2 is invalid. 242 * This code is used in __do_copy_from_user() of TT mode. 243 * XXX tt mode is gone, so maybe this isn't needed any more 244 */ 245 address = 0; 246 } 247 248 catcher = current->thread.fault_catcher; 249 if (!err) 250 goto out; 251 else if (catcher != NULL) { 252 current->thread.fault_addr = (void *) address; 253 UML_LONGJMP(catcher, 1); 254 } 255 else if (current->thread.fault_addr != NULL) 256 panic("fault_addr set but no fault catcher"); 257 else if (!is_user && arch_fixup(ip, regs)) 258 goto out; 259 260 if (!is_user) { 261 show_regs(container_of(regs, struct pt_regs, regs)); 262 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx", 263 address, ip); 264 } 265 266 show_segv_info(regs); 267 268 if (err == -EACCES) { 269 current->thread.arch.faultinfo = fi; 270 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 271 } else { 272 BUG_ON(err != -EFAULT); 273 current->thread.arch.faultinfo = fi; 274 force_sig_fault(SIGSEGV, si_code, (void __user *) address); 275 } 276 277 out: 278 if (regs) 279 current->thread.segv_regs = NULL; 280 281 return 0; 282 } 283 284 void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs) 285 { 286 int code, err; 287 if (!UPT_IS_USER(regs)) { 288 if (sig == SIGBUS) 289 printk(KERN_ERR "Bus error - the host /dev/shm or /tmp " 290 "mount likely just ran out of space\n"); 291 panic("Kernel mode signal %d", sig); 292 } 293 294 arch_examine_signal(sig, regs); 295 296 /* Is the signal layout for the signal known? 297 * Signal data must be scrubbed to prevent information leaks. 298 */ 299 code = si->si_code; 300 err = si->si_errno; 301 if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) { 302 struct faultinfo *fi = UPT_FAULTINFO(regs); 303 current->thread.arch.faultinfo = *fi; 304 force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi)); 305 } else { 306 printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n", 307 sig, code, err); 308 force_sig(sig); 309 } 310 } 311 312 void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs) 313 { 314 if (current->thread.fault_catcher != NULL) 315 UML_LONGJMP(current->thread.fault_catcher, 1); 316 else 317 relay_signal(sig, si, regs); 318 } 319 320 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) 321 { 322 do_IRQ(WINCH_IRQ, regs); 323 } 324 325 void trap_init(void) 326 { 327 } 328