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 p4d_t *p4d; 32 pud_t *pud; 33 pmd_t *pmd; 34 pte_t *pte; 35 int err = -EFAULT; 36 unsigned int flags = FAULT_FLAG_DEFAULT; 37 38 *code_out = SEGV_MAPERR; 39 40 /* 41 * If the fault was with pagefaults disabled, don't take the fault, just 42 * fail. 43 */ 44 if (faulthandler_disabled()) 45 goto out_nosemaphore; 46 47 if (is_user) 48 flags |= FAULT_FLAG_USER; 49 retry: 50 down_read(&mm->mmap_sem); 51 vma = find_vma(mm, address); 52 if (!vma) 53 goto out; 54 else if (vma->vm_start <= address) 55 goto good_area; 56 else if (!(vma->vm_flags & VM_GROWSDOWN)) 57 goto out; 58 else if (is_user && !ARCH_IS_STACKGROW(address)) 59 goto out; 60 else if (expand_stack(vma, address)) 61 goto out; 62 63 good_area: 64 *code_out = SEGV_ACCERR; 65 if (is_write) { 66 if (!(vma->vm_flags & VM_WRITE)) 67 goto out; 68 flags |= FAULT_FLAG_WRITE; 69 } else { 70 /* Don't require VM_READ|VM_EXEC for write faults! */ 71 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 72 goto out; 73 } 74 75 do { 76 vm_fault_t fault; 77 78 fault = handle_mm_fault(vma, address, flags); 79 80 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) 81 goto out_nosemaphore; 82 83 if (unlikely(fault & VM_FAULT_ERROR)) { 84 if (fault & VM_FAULT_OOM) { 85 goto out_of_memory; 86 } else if (fault & VM_FAULT_SIGSEGV) { 87 goto out; 88 } else if (fault & VM_FAULT_SIGBUS) { 89 err = -EACCES; 90 goto out; 91 } 92 BUG(); 93 } 94 if (flags & FAULT_FLAG_ALLOW_RETRY) { 95 if (fault & VM_FAULT_MAJOR) 96 current->maj_flt++; 97 else 98 current->min_flt++; 99 if (fault & VM_FAULT_RETRY) { 100 flags |= FAULT_FLAG_TRIED; 101 102 goto retry; 103 } 104 } 105 106 pgd = pgd_offset(mm, address); 107 p4d = p4d_offset(pgd, address); 108 pud = pud_offset(p4d, address); 109 pmd = pmd_offset(pud, address); 110 pte = pte_offset_kernel(pmd, address); 111 } while (!pte_present(*pte)); 112 err = 0; 113 /* 114 * The below warning was added in place of 115 * pte_mkyoung(); if (is_write) pte_mkdirty(); 116 * If it's triggered, we'd see normally a hang here (a clean pte is 117 * marked read-only to emulate the dirty bit). 118 * However, the generic code can mark a PTE writable but clean on a 119 * concurrent read fault, triggering this harmlessly. So comment it out. 120 */ 121 #if 0 122 WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte))); 123 #endif 124 flush_tlb_page(vma, address); 125 out: 126 up_read(&mm->mmap_sem); 127 out_nosemaphore: 128 return err; 129 130 out_of_memory: 131 /* 132 * We ran out of memory, call the OOM killer, and return the userspace 133 * (which will retry the fault, or kill us if we got oom-killed). 134 */ 135 up_read(&mm->mmap_sem); 136 if (!is_user) 137 goto out_nosemaphore; 138 pagefault_out_of_memory(); 139 return 0; 140 } 141 EXPORT_SYMBOL(handle_page_fault); 142 143 static void show_segv_info(struct uml_pt_regs *regs) 144 { 145 struct task_struct *tsk = current; 146 struct faultinfo *fi = UPT_FAULTINFO(regs); 147 148 if (!unhandled_signal(tsk, SIGSEGV)) 149 return; 150 151 if (!printk_ratelimit()) 152 return; 153 154 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x", 155 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, 156 tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi), 157 (void *)UPT_IP(regs), (void *)UPT_SP(regs), 158 fi->error_code); 159 160 print_vma_addr(KERN_CONT " in ", UPT_IP(regs)); 161 printk(KERN_CONT "\n"); 162 } 163 164 static void bad_segv(struct faultinfo fi, unsigned long ip) 165 { 166 current->thread.arch.faultinfo = fi; 167 force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi)); 168 } 169 170 void fatal_sigsegv(void) 171 { 172 force_sigsegv(SIGSEGV); 173 do_signal(¤t->thread.regs); 174 /* 175 * This is to tell gcc that we're not returning - do_signal 176 * can, in general, return, but in this case, it's not, since 177 * we just got a fatal SIGSEGV queued. 178 */ 179 os_dump_core(); 180 } 181 182 /** 183 * segv_handler() - the SIGSEGV handler 184 * @sig: the signal number 185 * @unused_si: the signal info struct; unused in this handler 186 * @regs: the ptrace register information 187 * 188 * The handler first extracts the faultinfo from the UML ptrace regs struct. 189 * If the userfault did not happen in an UML userspace process, bad_segv is called. 190 * Otherwise the signal did happen in a cloned userspace process, handle it. 191 */ 192 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) 193 { 194 struct faultinfo * fi = UPT_FAULTINFO(regs); 195 196 if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) { 197 show_segv_info(regs); 198 bad_segv(*fi, UPT_IP(regs)); 199 return; 200 } 201 segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs); 202 } 203 204 /* 205 * We give a *copy* of the faultinfo in the regs to segv. 206 * This must be done, since nesting SEGVs could overwrite 207 * the info in the regs. A pointer to the info then would 208 * give us bad data! 209 */ 210 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user, 211 struct uml_pt_regs *regs) 212 { 213 jmp_buf *catcher; 214 int si_code; 215 int err; 216 int is_write = FAULT_WRITE(fi); 217 unsigned long address = FAULT_ADDRESS(fi); 218 219 if (!is_user && regs) 220 current->thread.segv_regs = container_of(regs, struct pt_regs, regs); 221 222 if (!is_user && (address >= start_vm) && (address < end_vm)) { 223 flush_tlb_kernel_vm(); 224 goto out; 225 } 226 else if (current->mm == NULL) { 227 show_regs(container_of(regs, struct pt_regs, regs)); 228 panic("Segfault with no mm"); 229 } 230 else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) { 231 show_regs(container_of(regs, struct pt_regs, regs)); 232 panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx", 233 address, ip); 234 } 235 236 if (SEGV_IS_FIXABLE(&fi)) 237 err = handle_page_fault(address, ip, is_write, is_user, 238 &si_code); 239 else { 240 err = -EFAULT; 241 /* 242 * A thread accessed NULL, we get a fault, but CR2 is invalid. 243 * This code is used in __do_copy_from_user() of TT mode. 244 * XXX tt mode is gone, so maybe this isn't needed any more 245 */ 246 address = 0; 247 } 248 249 catcher = current->thread.fault_catcher; 250 if (!err) 251 goto out; 252 else if (catcher != NULL) { 253 current->thread.fault_addr = (void *) address; 254 UML_LONGJMP(catcher, 1); 255 } 256 else if (current->thread.fault_addr != NULL) 257 panic("fault_addr set but no fault catcher"); 258 else if (!is_user && arch_fixup(ip, regs)) 259 goto out; 260 261 if (!is_user) { 262 show_regs(container_of(regs, struct pt_regs, regs)); 263 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx", 264 address, ip); 265 } 266 267 show_segv_info(regs); 268 269 if (err == -EACCES) { 270 current->thread.arch.faultinfo = fi; 271 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 272 } else { 273 BUG_ON(err != -EFAULT); 274 current->thread.arch.faultinfo = fi; 275 force_sig_fault(SIGSEGV, si_code, (void __user *) address); 276 } 277 278 out: 279 if (regs) 280 current->thread.segv_regs = NULL; 281 282 return 0; 283 } 284 285 void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs) 286 { 287 int code, err; 288 if (!UPT_IS_USER(regs)) { 289 if (sig == SIGBUS) 290 printk(KERN_ERR "Bus error - the host /dev/shm or /tmp " 291 "mount likely just ran out of space\n"); 292 panic("Kernel mode signal %d", sig); 293 } 294 295 arch_examine_signal(sig, regs); 296 297 /* Is the signal layout for the signal known? 298 * Signal data must be scrubbed to prevent information leaks. 299 */ 300 code = si->si_code; 301 err = si->si_errno; 302 if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) { 303 struct faultinfo *fi = UPT_FAULTINFO(regs); 304 current->thread.arch.faultinfo = *fi; 305 force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi)); 306 } else { 307 printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n", 308 sig, code, err); 309 force_sig(sig); 310 } 311 } 312 313 void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs) 314 { 315 if (current->thread.fault_catcher != NULL) 316 UML_LONGJMP(current->thread.fault_catcher, 1); 317 else 318 relay_signal(sig, si, regs); 319 } 320 321 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) 322 { 323 do_IRQ(WINCH_IRQ, regs); 324 } 325 326 void trap_init(void) 327 { 328 } 329