xref: /openbmc/linux/arch/um/kernel/trap.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
1 /*
2  * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
3  * Licensed under the GPL
4  */
5 
6 #include "linux/kernel.h"
7 #include "asm/errno.h"
8 #include "linux/sched.h"
9 #include "linux/mm.h"
10 #include "linux/spinlock.h"
11 #include "linux/init.h"
12 #include "linux/ptrace.h"
13 #include "asm/semaphore.h"
14 #include "asm/pgtable.h"
15 #include "asm/pgalloc.h"
16 #include "asm/tlbflush.h"
17 #include "asm/a.out.h"
18 #include "asm/current.h"
19 #include "asm/irq.h"
20 #include "sysdep/sigcontext.h"
21 #include "kern_util.h"
22 #include "as-layout.h"
23 #include "arch.h"
24 #include "kern.h"
25 #include "chan_kern.h"
26 #include "mconsole_kern.h"
27 #include "mem.h"
28 #include "mem_kern.h"
29 #include "sysdep/sigcontext.h"
30 #include "sysdep/ptrace.h"
31 #include "os.h"
32 #ifdef CONFIG_MODE_SKAS
33 #include "skas.h"
34 #endif
35 #include "os.h"
36 
37 /* Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by segv(). */
38 int handle_page_fault(unsigned long address, unsigned long ip,
39 		      int is_write, int is_user, int *code_out)
40 {
41 	struct mm_struct *mm = current->mm;
42 	struct vm_area_struct *vma;
43 	pgd_t *pgd;
44 	pud_t *pud;
45 	pmd_t *pmd;
46 	pte_t *pte;
47 	int err = -EFAULT;
48 
49 	*code_out = SEGV_MAPERR;
50 
51 	/* If the fault was during atomic operation, don't take the fault, just
52 	 * fail. */
53 	if (in_atomic())
54 		goto out_nosemaphore;
55 
56 	down_read(&mm->mmap_sem);
57 	vma = find_vma(mm, address);
58 	if(!vma)
59 		goto out;
60 	else if(vma->vm_start <= address)
61 		goto good_area;
62 	else if(!(vma->vm_flags & VM_GROWSDOWN))
63 		goto out;
64 	else if(is_user && !ARCH_IS_STACKGROW(address))
65 		goto out;
66 	else if(expand_stack(vma, address))
67 		goto out;
68 
69 good_area:
70 	*code_out = SEGV_ACCERR;
71 	if(is_write && !(vma->vm_flags & VM_WRITE))
72 		goto out;
73 
74 	/* Don't require VM_READ|VM_EXEC for write faults! */
75 	if(!is_write && !(vma->vm_flags & (VM_READ | VM_EXEC)))
76 		goto out;
77 
78 	do {
79 survive:
80 		switch (handle_mm_fault(mm, vma, address, is_write)){
81 		case VM_FAULT_MINOR:
82 			current->min_flt++;
83 			break;
84 		case VM_FAULT_MAJOR:
85 			current->maj_flt++;
86 			break;
87 		case VM_FAULT_SIGBUS:
88 			err = -EACCES;
89 			goto out;
90 		case VM_FAULT_OOM:
91 			err = -ENOMEM;
92 			goto out_of_memory;
93 		default:
94 			BUG();
95 		}
96 		pgd = pgd_offset(mm, address);
97 		pud = pud_offset(pgd, address);
98 		pmd = pmd_offset(pud, address);
99 		pte = pte_offset_kernel(pmd, address);
100 	} while(!pte_present(*pte));
101 	err = 0;
102 	/* The below warning was added in place of
103 	 *	pte_mkyoung(); if (is_write) pte_mkdirty();
104 	 * If it's triggered, we'd see normally a hang here (a clean pte is
105 	 * marked read-only to emulate the dirty bit).
106 	 * However, the generic code can mark a PTE writable but clean on a
107 	 * concurrent read fault, triggering this harmlessly. So comment it out.
108 	 */
109 #if 0
110 	WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
111 #endif
112 	flush_tlb_page(vma, address);
113 out:
114 	up_read(&mm->mmap_sem);
115 out_nosemaphore:
116 	return(err);
117 
118 /*
119  * We ran out of memory, or some other thing happened to us that made
120  * us unable to handle the page fault gracefully.
121  */
122 out_of_memory:
123 	if (is_init(current)) {
124 		up_read(&mm->mmap_sem);
125 		yield();
126 		down_read(&mm->mmap_sem);
127 		goto survive;
128 	}
129 	goto out;
130 }
131 
132 static void bad_segv(struct faultinfo fi, unsigned long ip)
133 {
134 	struct siginfo si;
135 
136 	si.si_signo = SIGSEGV;
137 	si.si_code = SEGV_ACCERR;
138 	si.si_addr = (void __user *) FAULT_ADDRESS(fi);
139 	current->thread.arch.faultinfo = fi;
140 	force_sig_info(SIGSEGV, &si, current);
141 }
142 
143 static void segv_handler(int sig, union uml_pt_regs *regs)
144 {
145 	struct faultinfo * fi = UPT_FAULTINFO(regs);
146 
147 	if(UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)){
148 		bad_segv(*fi, UPT_IP(regs));
149 		return;
150 	}
151 	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
152 }
153 
154 /*
155  * We give a *copy* of the faultinfo in the regs to segv.
156  * This must be done, since nesting SEGVs could overwrite
157  * the info in the regs. A pointer to the info then would
158  * give us bad data!
159  */
160 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
161 		   union uml_pt_regs *regs)
162 {
163 	struct siginfo si;
164 	void *catcher;
165 	int err;
166 	int is_write = FAULT_WRITE(fi);
167 	unsigned long address = FAULT_ADDRESS(fi);
168 
169 	if(!is_user && (address >= start_vm) && (address < end_vm)){
170 		flush_tlb_kernel_vm();
171 		return 0;
172 	}
173 	else if(current->mm == NULL) {
174 		show_regs(container_of(regs, struct pt_regs, regs));
175   		panic("Segfault with no mm");
176 	}
177 
178 	if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
179 		err = handle_page_fault(address, ip, is_write, is_user, &si.si_code);
180 	else {
181 		err = -EFAULT;
182 		/* A thread accessed NULL, we get a fault, but CR2 is invalid.
183 		 * This code is used in __do_copy_from_user() of TT mode. */
184 		address = 0;
185 	}
186 
187 	catcher = current->thread.fault_catcher;
188 	if(!err)
189 		return 0;
190 	else if(catcher != NULL){
191 		current->thread.fault_addr = (void *) address;
192 		do_longjmp(catcher, 1);
193 	}
194 	else if(current->thread.fault_addr != NULL)
195 		panic("fault_addr set but no fault catcher");
196 	else if(!is_user && arch_fixup(ip, regs))
197 		return 0;
198 
199 	if(!is_user) {
200 		show_regs(container_of(regs, struct pt_regs, regs));
201 		panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
202 		      address, ip);
203 	}
204 
205 	if (err == -EACCES) {
206 		si.si_signo = SIGBUS;
207 		si.si_errno = 0;
208 		si.si_code = BUS_ADRERR;
209 		si.si_addr = (void __user *)address;
210 		current->thread.arch.faultinfo = fi;
211 		force_sig_info(SIGBUS, &si, current);
212 	} else if (err == -ENOMEM) {
213 		printk("VM: killing process %s\n", current->comm);
214 		do_exit(SIGKILL);
215 	} else {
216 		BUG_ON(err != -EFAULT);
217 		si.si_signo = SIGSEGV;
218 		si.si_addr = (void __user *) address;
219 		current->thread.arch.faultinfo = fi;
220 		force_sig_info(SIGSEGV, &si, current);
221 	}
222 	return 0;
223 }
224 
225 void relay_signal(int sig, union uml_pt_regs *regs)
226 {
227 	if(arch_handle_signal(sig, regs))
228 		return;
229 
230 	if(!UPT_IS_USER(regs)){
231 		if(sig == SIGBUS)
232 			printk("Bus error - the host /dev/shm or /tmp mount "
233 			       "likely just ran out of space\n");
234 		panic("Kernel mode signal %d", sig);
235 	}
236 
237 	current->thread.arch.faultinfo = *UPT_FAULTINFO(regs);
238 	force_sig(sig, current);
239 }
240 
241 static void bus_handler(int sig, union uml_pt_regs *regs)
242 {
243 	if(current->thread.fault_catcher != NULL)
244 		do_longjmp(current->thread.fault_catcher, 1);
245 	else relay_signal(sig, regs);
246 }
247 
248 static void winch(int sig, union uml_pt_regs *regs)
249 {
250 	do_IRQ(WINCH_IRQ, regs);
251 }
252 
253 const struct kern_handlers handlinfo_kern = {
254 	.relay_signal = relay_signal,
255 	.winch = winch,
256 	.bus_handler = bus_handler,
257 	.page_fault = segv_handler,
258 	.sigio_handler = sigio_handler,
259 	.timer_handler = timer_handler
260 };
261 
262 void trap_init(void)
263 {
264 }
265