1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
4  *
5  * Derived from MIPS:
6  * Copyright (C) 1995 - 2000 by Ralf Baechle
7  */
8 #include <linux/context_tracking.h>
9 #include <linux/signal.h>
10 #include <linux/sched.h>
11 #include <linux/interrupt.h>
12 #include <linux/kernel.h>
13 #include <linux/entry-common.h>
14 #include <linux/errno.h>
15 #include <linux/string.h>
16 #include <linux/types.h>
17 #include <linux/ptrace.h>
18 #include <linux/ratelimit.h>
19 #include <linux/mman.h>
20 #include <linux/mm.h>
21 #include <linux/smp.h>
22 #include <linux/kdebug.h>
23 #include <linux/perf_event.h>
24 #include <linux/uaccess.h>
25 #include <linux/kfence.h>
26 
27 #include <asm/branch.h>
28 #include <asm/exception.h>
29 #include <asm/mmu_context.h>
30 #include <asm/ptrace.h>
31 
32 int show_unhandled_signals = 1;
33 
no_context(struct pt_regs * regs,unsigned long write,unsigned long address)34 static void __kprobes no_context(struct pt_regs *regs,
35 			unsigned long write, unsigned long address)
36 {
37 	const int field = sizeof(unsigned long) * 2;
38 
39 	/* Are we prepared to handle this kernel fault?	 */
40 	if (fixup_exception(regs))
41 		return;
42 
43 	if (kfence_handle_page_fault(address, write, regs))
44 		return;
45 
46 	/*
47 	 * Oops. The kernel tried to access some bad page. We'll have to
48 	 * terminate things with extreme prejudice.
49 	 */
50 	bust_spinlocks(1);
51 
52 	pr_alert("CPU %d Unable to handle kernel paging request at "
53 	       "virtual address %0*lx, era == %0*lx, ra == %0*lx\n",
54 	       raw_smp_processor_id(), field, address, field, regs->csr_era,
55 	       field,  regs->regs[1]);
56 	die("Oops", regs);
57 }
58 
do_out_of_memory(struct pt_regs * regs,unsigned long write,unsigned long address)59 static void __kprobes do_out_of_memory(struct pt_regs *regs,
60 			unsigned long write, unsigned long address)
61 {
62 	/*
63 	 * We ran out of memory, call the OOM killer, and return the userspace
64 	 * (which will retry the fault, or kill us if we got oom-killed).
65 	 */
66 	if (!user_mode(regs)) {
67 		no_context(regs, write, address);
68 		return;
69 	}
70 	pagefault_out_of_memory();
71 }
72 
do_sigbus(struct pt_regs * regs,unsigned long write,unsigned long address,int si_code)73 static void __kprobes do_sigbus(struct pt_regs *regs,
74 		unsigned long write, unsigned long address, int si_code)
75 {
76 	/* Kernel mode? Handle exceptions or die */
77 	if (!user_mode(regs)) {
78 		no_context(regs, write, address);
79 		return;
80 	}
81 
82 	/*
83 	 * Send a sigbus, regardless of whether we were in kernel
84 	 * or user mode.
85 	 */
86 	current->thread.csr_badvaddr = address;
87 	current->thread.trap_nr = read_csr_excode();
88 	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
89 }
90 
do_sigsegv(struct pt_regs * regs,unsigned long write,unsigned long address,int si_code)91 static void __kprobes do_sigsegv(struct pt_regs *regs,
92 		unsigned long write, unsigned long address, int si_code)
93 {
94 	const int field = sizeof(unsigned long) * 2;
95 	static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
96 
97 	/* Kernel mode? Handle exceptions or die */
98 	if (!user_mode(regs)) {
99 		no_context(regs, write, address);
100 		return;
101 	}
102 
103 	/* User mode accesses just cause a SIGSEGV */
104 	current->thread.csr_badvaddr = address;
105 	if (!write)
106 		current->thread.error_code = 1;
107 	else
108 		current->thread.error_code = 2;
109 	current->thread.trap_nr = read_csr_excode();
110 
111 	if (show_unhandled_signals &&
112 	    unhandled_signal(current, SIGSEGV) && __ratelimit(&ratelimit_state)) {
113 		pr_info("do_page_fault(): sending SIGSEGV to %s for invalid %s %0*lx\n",
114 			current->comm,
115 			write ? "write access to" : "read access from",
116 			field, address);
117 		pr_info("era = %0*lx in", field,
118 			(unsigned long) regs->csr_era);
119 		print_vma_addr(KERN_CONT " ", regs->csr_era);
120 		pr_cont("\n");
121 		pr_info("ra  = %0*lx in", field,
122 			(unsigned long) regs->regs[1]);
123 		print_vma_addr(KERN_CONT " ", regs->regs[1]);
124 		pr_cont("\n");
125 	}
126 	force_sig_fault(SIGSEGV, si_code, (void __user *)address);
127 }
128 
129 /*
130  * This routine handles page faults.  It determines the address,
131  * and the problem, and then passes it off to one of the appropriate
132  * routines.
133  */
__do_page_fault(struct pt_regs * regs,unsigned long write,unsigned long address)134 static void __kprobes __do_page_fault(struct pt_regs *regs,
135 			unsigned long write, unsigned long address)
136 {
137 	int si_code = SEGV_MAPERR;
138 	unsigned int flags = FAULT_FLAG_DEFAULT;
139 	struct task_struct *tsk = current;
140 	struct mm_struct *mm = tsk->mm;
141 	struct vm_area_struct *vma = NULL;
142 	vm_fault_t fault;
143 
144 	if (kprobe_page_fault(regs, current->thread.trap_nr))
145 		return;
146 
147 	/*
148 	 * We fault-in kernel-space virtual memory on-demand. The
149 	 * 'reference' page table is init_mm.pgd.
150 	 *
151 	 * NOTE! We MUST NOT take any locks for this case. We may
152 	 * be in an interrupt or a critical region, and should
153 	 * only copy the information from the master page table,
154 	 * nothing more.
155 	 */
156 	if (address & __UA_LIMIT) {
157 		if (!user_mode(regs))
158 			no_context(regs, write, address);
159 		else
160 			do_sigsegv(regs, write, address, si_code);
161 		return;
162 	}
163 
164 	/*
165 	 * If we're in an interrupt or have no user
166 	 * context, we must not take the fault..
167 	 */
168 	if (faulthandler_disabled() || !mm) {
169 		do_sigsegv(regs, write, address, si_code);
170 		return;
171 	}
172 
173 	if (user_mode(regs))
174 		flags |= FAULT_FLAG_USER;
175 
176 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
177 retry:
178 	vma = lock_mm_and_find_vma(mm, address, regs);
179 	if (unlikely(!vma))
180 		goto bad_area_nosemaphore;
181 	goto good_area;
182 
183 /*
184  * Something tried to access memory that isn't in our memory map..
185  * Fix it, but check if it's kernel or user first..
186  */
187 bad_area:
188 	mmap_read_unlock(mm);
189 bad_area_nosemaphore:
190 	do_sigsegv(regs, write, address, si_code);
191 	return;
192 
193 /*
194  * Ok, we have a good vm_area for this memory access, so
195  * we can handle it..
196  */
197 good_area:
198 	si_code = SEGV_ACCERR;
199 
200 	if (write) {
201 		flags |= FAULT_FLAG_WRITE;
202 		if (!(vma->vm_flags & VM_WRITE))
203 			goto bad_area;
204 	} else {
205 		if (!(vma->vm_flags & VM_READ) && address != exception_era(regs))
206 			goto bad_area;
207 		if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs))
208 			goto bad_area;
209 	}
210 
211 	/*
212 	 * If for any reason at all we couldn't handle the fault,
213 	 * make sure we exit gracefully rather than endlessly redo
214 	 * the fault.
215 	 */
216 	fault = handle_mm_fault(vma, address, flags, regs);
217 
218 	if (fault_signal_pending(fault, regs)) {
219 		if (!user_mode(regs))
220 			no_context(regs, write, address);
221 		return;
222 	}
223 
224 	/* The fault is fully completed (including releasing mmap lock) */
225 	if (fault & VM_FAULT_COMPLETED)
226 		return;
227 
228 	if (unlikely(fault & VM_FAULT_RETRY)) {
229 		flags |= FAULT_FLAG_TRIED;
230 
231 		/*
232 		 * No need to mmap_read_unlock(mm) as we would
233 		 * have already released it in __lock_page_or_retry
234 		 * in mm/filemap.c.
235 		 */
236 		goto retry;
237 	}
238 	if (unlikely(fault & VM_FAULT_ERROR)) {
239 		mmap_read_unlock(mm);
240 		if (fault & VM_FAULT_OOM) {
241 			do_out_of_memory(regs, write, address);
242 			return;
243 		} else if (fault & VM_FAULT_SIGSEGV) {
244 			do_sigsegv(regs, write, address, si_code);
245 			return;
246 		} else if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
247 			do_sigbus(regs, write, address, si_code);
248 			return;
249 		}
250 		BUG();
251 	}
252 
253 	mmap_read_unlock(mm);
254 }
255 
do_page_fault(struct pt_regs * regs,unsigned long write,unsigned long address)256 asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
257 			unsigned long write, unsigned long address)
258 {
259 	irqentry_state_t state = irqentry_enter(regs);
260 
261 	/* Enable interrupt if enabled in parent context */
262 	if (likely(regs->csr_prmd & CSR_PRMD_PIE))
263 		local_irq_enable();
264 
265 	__do_page_fault(regs, write, address);
266 
267 	local_irq_disable();
268 
269 	irqentry_exit(regs, state);
270 }
271