1 // SPDX-License-Identifier: GPL-2.0 2 3 /* 4 * Stack trace utility functions etc. 5 * 6 * Copyright 2008 Christoph Hellwig, IBM Corp. 7 * Copyright 2018 SUSE Linux GmbH 8 * Copyright 2018 Nick Piggin, Michael Ellerman, IBM Corp. 9 */ 10 11 #include <linux/delay.h> 12 #include <linux/export.h> 13 #include <linux/kallsyms.h> 14 #include <linux/module.h> 15 #include <linux/nmi.h> 16 #include <linux/sched.h> 17 #include <linux/sched/debug.h> 18 #include <linux/sched/task_stack.h> 19 #include <linux/stacktrace.h> 20 #include <asm/ptrace.h> 21 #include <asm/processor.h> 22 #include <linux/ftrace.h> 23 #include <asm/kprobes.h> 24 25 #include <asm/paca.h> 26 27 void __no_sanitize_address arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie, 28 struct task_struct *task, struct pt_regs *regs) 29 { 30 unsigned long sp; 31 32 if (regs && !consume_entry(cookie, regs->nip)) 33 return; 34 35 if (regs) 36 sp = regs->gpr[1]; 37 else if (task == current) 38 sp = current_stack_frame(); 39 else 40 sp = task->thread.ksp; 41 42 for (;;) { 43 unsigned long *stack = (unsigned long *) sp; 44 unsigned long newsp, ip; 45 46 if (!validate_sp(sp, task, STACK_FRAME_OVERHEAD)) 47 return; 48 49 newsp = stack[0]; 50 ip = stack[STACK_FRAME_LR_SAVE]; 51 52 if (!consume_entry(cookie, ip)) 53 return; 54 55 sp = newsp; 56 } 57 } 58 59 /* 60 * This function returns an error if it detects any unreliable features of the 61 * stack. Otherwise it guarantees that the stack trace is reliable. 62 * 63 * If the task is not 'current', the caller *must* ensure the task is inactive. 64 */ 65 int __no_sanitize_address arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, 66 void *cookie, struct task_struct *task) 67 { 68 unsigned long sp; 69 unsigned long newsp; 70 unsigned long stack_page = (unsigned long)task_stack_page(task); 71 unsigned long stack_end; 72 int graph_idx = 0; 73 bool firstframe; 74 75 stack_end = stack_page + THREAD_SIZE; 76 if (!is_idle_task(task)) { 77 /* 78 * For user tasks, this is the SP value loaded on 79 * kernel entry, see "PACAKSAVE(r13)" in _switch() and 80 * system_call_common()/EXCEPTION_PROLOG_COMMON(). 81 * 82 * Likewise for non-swapper kernel threads, 83 * this also happens to be the top of the stack 84 * as setup by copy_thread(). 85 * 86 * Note that stack backlinks are not properly setup by 87 * copy_thread() and thus, a forked task() will have 88 * an unreliable stack trace until it's been 89 * _switch()'ed to for the first time. 90 */ 91 stack_end -= STACK_FRAME_OVERHEAD + sizeof(struct pt_regs); 92 } else { 93 /* 94 * idle tasks have a custom stack layout, 95 * c.f. cpu_idle_thread_init(). 96 */ 97 stack_end -= STACK_FRAME_OVERHEAD; 98 } 99 100 if (task == current) 101 sp = current_stack_frame(); 102 else 103 sp = task->thread.ksp; 104 105 if (sp < stack_page + sizeof(struct thread_struct) || 106 sp > stack_end - STACK_FRAME_MIN_SIZE) { 107 return -EINVAL; 108 } 109 110 for (firstframe = true; sp != stack_end; 111 firstframe = false, sp = newsp) { 112 unsigned long *stack = (unsigned long *) sp; 113 unsigned long ip; 114 115 /* sanity check: ABI requires SP to be aligned 16 bytes. */ 116 if (sp & 0xF) 117 return -EINVAL; 118 119 newsp = stack[0]; 120 /* Stack grows downwards; unwinder may only go up. */ 121 if (newsp <= sp) 122 return -EINVAL; 123 124 if (newsp != stack_end && 125 newsp > stack_end - STACK_FRAME_MIN_SIZE) { 126 return -EINVAL; /* invalid backlink, too far up. */ 127 } 128 129 /* 130 * We can only trust the bottom frame's backlink, the 131 * rest of the frame may be uninitialized, continue to 132 * the next. 133 */ 134 if (firstframe) 135 continue; 136 137 /* Mark stacktraces with exception frames as unreliable. */ 138 if (sp <= stack_end - STACK_INT_FRAME_SIZE && 139 stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) { 140 return -EINVAL; 141 } 142 143 /* Examine the saved LR: it must point into kernel code. */ 144 ip = stack[STACK_FRAME_LR_SAVE]; 145 if (!__kernel_text_address(ip)) 146 return -EINVAL; 147 148 /* 149 * FIXME: IMHO these tests do not belong in 150 * arch-dependent code, they are generic. 151 */ 152 ip = ftrace_graph_ret_addr(task, &graph_idx, ip, stack); 153 #ifdef CONFIG_KPROBES 154 /* 155 * Mark stacktraces with kretprobed functions on them 156 * as unreliable. 157 */ 158 if (ip == (unsigned long)__kretprobe_trampoline) 159 return -EINVAL; 160 #endif 161 162 if (!consume_entry(cookie, ip)) 163 return -EINVAL; 164 } 165 return 0; 166 } 167 168 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI) 169 static void handle_backtrace_ipi(struct pt_regs *regs) 170 { 171 nmi_cpu_backtrace(regs); 172 } 173 174 static void raise_backtrace_ipi(cpumask_t *mask) 175 { 176 struct paca_struct *p; 177 unsigned int cpu; 178 u64 delay_us; 179 180 for_each_cpu(cpu, mask) { 181 if (cpu == smp_processor_id()) { 182 handle_backtrace_ipi(NULL); 183 continue; 184 } 185 186 delay_us = 5 * USEC_PER_SEC; 187 188 if (smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, delay_us)) { 189 // Now wait up to 5s for the other CPU to do its backtrace 190 while (cpumask_test_cpu(cpu, mask) && delay_us) { 191 udelay(1); 192 delay_us--; 193 } 194 195 // Other CPU cleared itself from the mask 196 if (delay_us) 197 continue; 198 } 199 200 p = paca_ptrs[cpu]; 201 202 cpumask_clear_cpu(cpu, mask); 203 204 pr_warn("CPU %d didn't respond to backtrace IPI, inspecting paca.\n", cpu); 205 if (!virt_addr_valid(p)) { 206 pr_warn("paca pointer appears corrupt? (%px)\n", p); 207 continue; 208 } 209 210 pr_warn("irq_soft_mask: 0x%02x in_mce: %d in_nmi: %d", 211 p->irq_soft_mask, p->in_mce, p->in_nmi); 212 213 if (virt_addr_valid(p->__current)) 214 pr_cont(" current: %d (%s)\n", p->__current->pid, 215 p->__current->comm); 216 else 217 pr_cont(" current pointer corrupt? (%px)\n", p->__current); 218 219 pr_warn("Back trace of paca->saved_r1 (0x%016llx) (possibly stale):\n", p->saved_r1); 220 show_stack(p->__current, (unsigned long *)p->saved_r1, KERN_WARNING); 221 } 222 } 223 224 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self) 225 { 226 nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi); 227 } 228 #endif /* defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI) */ 229