arch/powerpc/kernel/stacktrace.c

   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/export.h>
  12 #include <linux/kallsyms.h>
  13 #include <linux/module.h>
  14 #include <linux/nmi.h>
  15 #include <linux/sched.h>
  16 #include <linux/sched/debug.h>
  17 #include <linux/sched/task_stack.h>
  18 #include <linux/stacktrace.h>
  19 #include <asm/ptrace.h>
  20 #include <asm/processor.h>
  21 #include <linux/ftrace.h>
  22 #include <asm/kprobes.h>
  23
  24 #include <asm/paca.h>
  25
  26 /*
  27  * Save stack-backtrace addresses into a stack_trace buffer.
  28  */
  29 static void save_context_stack(struct stack_trace *trace, unsigned long sp,
  30                         struct task_struct *tsk, int savesched)
  31 {
  32         for (;;) {
  33                 unsigned long *stack = (unsigned long *) sp;
  34                 unsigned long newsp, ip;
  35
  36                 if (!validate_sp(sp, tsk, STACK_FRAME_OVERHEAD))
  37                         return;
  38
  39                 newsp = stack[0];
  40                 ip = stack[STACK_FRAME_LR_SAVE];
  41
  42                 if (savesched || !in_sched_functions(ip)) {
  43                         if (!trace->skip)
  44                                 trace->entries[trace->nr_entries++] = ip;
  45                         else
  46                                 trace->skip--;
  47                 }
  48
  49                 if (trace->nr_entries >= trace->max_entries)
  50                         return;
  51
  52                 sp = newsp;
  53         }
  54 }
  55
  56 void save_stack_trace(struct stack_trace *trace)
  57 {
  58         unsigned long sp;
  59
  60         sp = current_stack_pointer();
  61
  62         save_context_stack(trace, sp, current, 1);
  63 }
  64 EXPORT_SYMBOL_GPL(save_stack_trace);
  65
  66 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
  67 {
  68         unsigned long sp;
  69
  70         if (!try_get_task_stack(tsk))
  71                 return;
  72
  73         if (tsk == current)
  74                 sp = current_stack_pointer();
  75         else
  76                 sp = tsk->thread.ksp;
  77
  78         save_context_stack(trace, sp, tsk, 0);
  79
  80         put_task_stack(tsk);
  81 }
  82 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
  83
  84 void
  85 save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
  86 {
  87         save_context_stack(trace, regs->gpr[1], current, 0);
  88 }
  89 EXPORT_SYMBOL_GPL(save_stack_trace_regs);
  90
  91 #ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
  92 /*
  93  * This function returns an error if it detects any unreliable features of the
  94  * stack.  Otherwise it guarantees that the stack trace is reliable.
  95  *
  96  * If the task is not 'current', the caller *must* ensure the task is inactive.
  97  */
  98 static int __save_stack_trace_tsk_reliable(struct task_struct *tsk,
  99                                            struct stack_trace *trace)
 100 {
 101         unsigned long sp;
 102         unsigned long newsp;
 103         unsigned long stack_page = (unsigned long)task_stack_page(tsk);
 104         unsigned long stack_end;
 105         int graph_idx = 0;
 106         bool firstframe;
 107
 108         stack_end = stack_page + THREAD_SIZE;
 109         if (!is_idle_task(tsk)) {
 110                 /*
 111                  * For user tasks, this is the SP value loaded on
 112                  * kernel entry, see "PACAKSAVE(r13)" in _switch() and
 113                  * system_call_common()/EXCEPTION_PROLOG_COMMON().
 114                  *
 115                  * Likewise for non-swapper kernel threads,
 116                  * this also happens to be the top of the stack
 117                  * as setup by copy_thread().
 118                  *
 119                  * Note that stack backlinks are not properly setup by
 120                  * copy_thread() and thus, a forked task() will have
 121                  * an unreliable stack trace until it's been
 122                  * _switch()'ed to for the first time.
 123                  */
 124                 stack_end -= STACK_FRAME_OVERHEAD + sizeof(struct pt_regs);
 125         } else {
 126                 /*
 127                  * idle tasks have a custom stack layout,
 128                  * c.f. cpu_idle_thread_init().
 129                  */
 130                 stack_end -= STACK_FRAME_OVERHEAD;
 131         }
 132
 133         if (tsk == current)
 134                 sp = current_stack_pointer();
 135         else
 136                 sp = tsk->thread.ksp;
 137
 138         if (sp < stack_page + sizeof(struct thread_struct) ||
 139             sp > stack_end - STACK_FRAME_MIN_SIZE) {
 140                 return -EINVAL;
 141         }
 142
 143         for (firstframe = true; sp != stack_end;
 144              firstframe = false, sp = newsp) {
 145                 unsigned long *stack = (unsigned long *) sp;
 146                 unsigned long ip;
 147
 148                 /* sanity check: ABI requires SP to be aligned 16 bytes. */
 149                 if (sp & 0xF)
 150                         return -EINVAL;
 151
 152                 newsp = stack[0];
 153                 /* Stack grows downwards; unwinder may only go up. */
 154                 if (newsp <= sp)
 155                         return -EINVAL;
 156
 157                 if (newsp != stack_end &&
 158                     newsp > stack_end - STACK_FRAME_MIN_SIZE) {
 159                         return -EINVAL; /* invalid backlink, too far up. */
 160                 }
 161
 162                 /*
 163                  * We can only trust the bottom frame's backlink, the
 164                  * rest of the frame may be uninitialized, continue to
 165                  * the next.
 166                  */
 167                 if (firstframe)
 168                         continue;
 169
 170                 /* Mark stacktraces with exception frames as unreliable. */
 171                 if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
 172                     stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
 173                         return -EINVAL;
 174                 }
 175
 176                 /* Examine the saved LR: it must point into kernel code. */
 177                 ip = stack[STACK_FRAME_LR_SAVE];
 178                 if (!__kernel_text_address(ip))
 179                         return -EINVAL;
 180
 181                 /*
 182                  * FIXME: IMHO these tests do not belong in
 183                  * arch-dependent code, they are generic.
 184                  */
 185                 ip = ftrace_graph_ret_addr(tsk, &graph_idx, ip, NULL);
 186 #ifdef CONFIG_KPROBES
 187                 /*
 188                  * Mark stacktraces with kretprobed functions on them
 189                  * as unreliable.
 190                  */
 191                 if (ip == (unsigned long)kretprobe_trampoline)
 192                         return -EINVAL;
 193 #endif
 194
 195                 if (trace->nr_entries >= trace->max_entries)
 196                         return -E2BIG;
 197                 if (!trace->skip)
 198                         trace->entries[trace->nr_entries++] = ip;
 199                 else
 200                         trace->skip--;
 201         }
 202         return 0;
 203 }
 204
 205 int save_stack_trace_tsk_reliable(struct task_struct *tsk,
 206                                   struct stack_trace *trace)
 207 {
 208         int ret;
 209
 210         /*
 211          * If the task doesn't have a stack (e.g., a zombie), the stack is
 212          * "reliably" empty.
 213          */
 214         if (!try_get_task_stack(tsk))
 215                 return 0;
 216
 217         ret = __save_stack_trace_tsk_reliable(tsk, trace);
 218
 219         put_task_stack(tsk);
 220
 221         return ret;
 222 }
 223 #endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
 224
 225 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI)
 226 static void handle_backtrace_ipi(struct pt_regs *regs)
 227 {
 228         nmi_cpu_backtrace(regs);
 229 }
 230
 231 static void raise_backtrace_ipi(cpumask_t *mask)
 232 {
 233         unsigned int cpu;
 234
 235         for_each_cpu(cpu, mask) {
 236                 if (cpu == smp_processor_id())
 237                         handle_backtrace_ipi(NULL);
 238                 else
 239                         smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, 5 * USEC_PER_SEC);
 240         }
 241
 242         for_each_cpu(cpu, mask) {
 243                 struct paca_struct *p = paca_ptrs[cpu];
 244
 245                 cpumask_clear_cpu(cpu, mask);
 246
 247                 pr_warn("CPU %d didn't respond to backtrace IPI, inspecting paca.\n", cpu);
 248                 if (!virt_addr_valid(p)) {
 249                         pr_warn("paca pointer appears corrupt? (%px)\n", p);
 250                         continue;
 251                 }
 252
 253                 pr_warn("irq_soft_mask: 0x%02x in_mce: %d in_nmi: %d",
 254                         p->irq_soft_mask, p->in_mce, p->in_nmi);
 255
 256                 if (virt_addr_valid(p->__current))
 257                         pr_cont(" current: %d (%s)\n", p->__current->pid,
 258                                 p->__current->comm);
 259                 else
 260                         pr_cont(" current pointer corrupt? (%px)\n", p->__current);
 261
 262                 pr_warn("Back trace of paca->saved_r1 (0x%016llx) (possibly stale):\n", p->saved_r1);
 263                 show_stack(p->__current, (unsigned long *)p->saved_r1);
 264         }
 265 }
 266
 267 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
 268 {
 269         nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
 270 }
 271 #endif /* defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI) */