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TOMOYO Linux Cross Reference
Linux/arch/x86/kernel/unwind_frame.c

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  1 #include <linux/sched.h>
  2 #include <linux/sched/task.h>
  3 #include <linux/sched/task_stack.h>
  4 #include <linux/interrupt.h>
  5 #include <asm/sections.h>
  6 #include <asm/ptrace.h>
  7 #include <asm/bitops.h>
  8 #include <asm/stacktrace.h>
  9 #include <asm/unwind.h>
 10 
 11 #define FRAME_HEADER_SIZE (sizeof(long) * 2)
 12 
 13 unsigned long unwind_get_return_address(struct unwind_state *state)
 14 {
 15         if (unwind_done(state))
 16                 return 0;
 17 
 18         return __kernel_text_address(state->ip) ? state->ip : 0;
 19 }
 20 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 21 
 22 unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
 23 {
 24         if (unwind_done(state))
 25                 return NULL;
 26 
 27         return state->regs ? &state->regs->ip : state->bp + 1;
 28 }
 29 
 30 static void unwind_dump(struct unwind_state *state)
 31 {
 32         static bool dumped_before = false;
 33         bool prev_zero, zero = false;
 34         unsigned long word, *sp;
 35         struct stack_info stack_info = {0};
 36         unsigned long visit_mask = 0;
 37 
 38         if (dumped_before)
 39                 return;
 40 
 41         dumped_before = true;
 42 
 43         printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n",
 44                         state->stack_info.type, state->stack_info.next_sp,
 45                         state->stack_mask, state->graph_idx);
 46 
 47         for (sp = PTR_ALIGN(state->orig_sp, sizeof(long)); sp;
 48              sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
 49                 if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
 50                         break;
 51 
 52                 for (; sp < stack_info.end; sp++) {
 53 
 54                         word = READ_ONCE_NOCHECK(*sp);
 55 
 56                         prev_zero = zero;
 57                         zero = word == 0;
 58 
 59                         if (zero) {
 60                                 if (!prev_zero)
 61                                         printk_deferred("%p: %0*x ...\n",
 62                                                         sp, BITS_PER_LONG/4, 0);
 63                                 continue;
 64                         }
 65 
 66                         printk_deferred("%p: %0*lx (%pB)\n",
 67                                         sp, BITS_PER_LONG/4, word, (void *)word);
 68                 }
 69         }
 70 }
 71 
 72 static size_t regs_size(struct pt_regs *regs)
 73 {
 74         /* x86_32 regs from kernel mode are two words shorter: */
 75         if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs))
 76                 return sizeof(*regs) - 2*sizeof(long);
 77 
 78         return sizeof(*regs);
 79 }
 80 
 81 static bool in_entry_code(unsigned long ip)
 82 {
 83         char *addr = (char *)ip;
 84 
 85         if (addr >= __entry_text_start && addr < __entry_text_end)
 86                 return true;
 87 
 88         if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
 89                 return true;
 90 
 91         return false;
 92 }
 93 
 94 static inline unsigned long *last_frame(struct unwind_state *state)
 95 {
 96         return (unsigned long *)task_pt_regs(state->task) - 2;
 97 }
 98 
 99 static bool is_last_frame(struct unwind_state *state)
100 {
101         return state->bp == last_frame(state);
102 }
103 
104 #ifdef CONFIG_X86_32
105 #define GCC_REALIGN_WORDS 3
106 #else
107 #define GCC_REALIGN_WORDS 1
108 #endif
109 
110 static inline unsigned long *last_aligned_frame(struct unwind_state *state)
111 {
112         return last_frame(state) - GCC_REALIGN_WORDS;
113 }
114 
115 static bool is_last_aligned_frame(struct unwind_state *state)
116 {
117         unsigned long *last_bp = last_frame(state);
118         unsigned long *aligned_bp = last_aligned_frame(state);
119 
120         /*
121          * GCC can occasionally decide to realign the stack pointer and change
122          * the offset of the stack frame in the prologue of a function called
123          * by head/entry code.  Examples:
124          *
125          * <start_secondary>:
126          *      push   %edi
127          *      lea    0x8(%esp),%edi
128          *      and    $0xfffffff8,%esp
129          *      pushl  -0x4(%edi)
130          *      push   %ebp
131          *      mov    %esp,%ebp
132          *
133          * <x86_64_start_kernel>:
134          *      lea    0x8(%rsp),%r10
135          *      and    $0xfffffffffffffff0,%rsp
136          *      pushq  -0x8(%r10)
137          *      push   %rbp
138          *      mov    %rsp,%rbp
139          *
140          * After aligning the stack, it pushes a duplicate copy of the return
141          * address before pushing the frame pointer.
142          */
143         return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
144 }
145 
146 static bool is_last_ftrace_frame(struct unwind_state *state)
147 {
148         unsigned long *last_bp = last_frame(state);
149         unsigned long *last_ftrace_bp = last_bp - 3;
150 
151         /*
152          * When unwinding from an ftrace handler of a function called by entry
153          * code, the stack layout of the last frame is:
154          *
155          *   bp
156          *   parent ret addr
157          *   bp
158          *   function ret addr
159          *   parent ret addr
160          *   pt_regs
161          *   -----------------
162          */
163         return (state->bp == last_ftrace_bp &&
164                 *state->bp == *(state->bp + 2) &&
165                 *(state->bp + 1) == *(state->bp + 4));
166 }
167 
168 static bool is_last_task_frame(struct unwind_state *state)
169 {
170         return is_last_frame(state) || is_last_aligned_frame(state) ||
171                is_last_ftrace_frame(state);
172 }
173 
174 /*
175  * This determines if the frame pointer actually contains an encoded pointer to
176  * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
177  */
178 #ifdef CONFIG_X86_64
179 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
180 {
181         unsigned long regs = (unsigned long)bp;
182 
183         if (!(regs & 0x1))
184                 return NULL;
185 
186         return (struct pt_regs *)(regs & ~0x1);
187 }
188 #else
189 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
190 {
191         unsigned long regs = (unsigned long)bp;
192 
193         if (regs & 0x80000000)
194                 return NULL;
195 
196         return (struct pt_regs *)(regs | 0x80000000);
197 }
198 #endif
199 
200 #ifdef CONFIG_X86_32
201 #define KERNEL_REGS_SIZE (sizeof(struct pt_regs) - 2*sizeof(long))
202 #else
203 #define KERNEL_REGS_SIZE (sizeof(struct pt_regs))
204 #endif
205 
206 static bool update_stack_state(struct unwind_state *state,
207                                unsigned long *next_bp)
208 {
209         struct stack_info *info = &state->stack_info;
210         enum stack_type prev_type = info->type;
211         struct pt_regs *regs;
212         unsigned long *frame, *prev_frame_end, *addr_p, addr;
213         size_t len;
214 
215         if (state->regs)
216                 prev_frame_end = (void *)state->regs + regs_size(state->regs);
217         else
218                 prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;
219 
220         /* Is the next frame pointer an encoded pointer to pt_regs? */
221         regs = decode_frame_pointer(next_bp);
222         if (regs) {
223                 frame = (unsigned long *)regs;
224                 len = KERNEL_REGS_SIZE;
225                 state->got_irq = true;
226         } else {
227                 frame = next_bp;
228                 len = FRAME_HEADER_SIZE;
229         }
230 
231         /*
232          * If the next bp isn't on the current stack, switch to the next one.
233          *
234          * We may have to traverse multiple stacks to deal with the possibility
235          * that info->next_sp could point to an empty stack and the next bp
236          * could be on a subsequent stack.
237          */
238         while (!on_stack(info, frame, len))
239                 if (get_stack_info(info->next_sp, state->task, info,
240                                    &state->stack_mask))
241                         return false;
242 
243         /* Make sure it only unwinds up and doesn't overlap the prev frame: */
244         if (state->orig_sp && state->stack_info.type == prev_type &&
245             frame < prev_frame_end)
246                 return false;
247 
248         /*
249          * On 32-bit with user mode regs, make sure the last two regs are safe
250          * to access:
251          */
252         if (IS_ENABLED(CONFIG_X86_32) && regs && user_mode(regs) &&
253             !on_stack(info, frame, len + 2*sizeof(long)))
254                 return false;
255 
256         /* Move state to the next frame: */
257         if (regs) {
258                 state->regs = regs;
259                 state->bp = NULL;
260         } else {
261                 state->bp = next_bp;
262                 state->regs = NULL;
263         }
264 
265         /* Save the return address: */
266         if (state->regs && user_mode(state->regs))
267                 state->ip = 0;
268         else {
269                 addr_p = unwind_get_return_address_ptr(state);
270                 addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
271                 state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
272                                                   addr, addr_p);
273         }
274 
275         /* Save the original stack pointer for unwind_dump(): */
276         if (!state->orig_sp)
277                 state->orig_sp = frame;
278 
279         return true;
280 }
281 
282 bool unwind_next_frame(struct unwind_state *state)
283 {
284         struct pt_regs *regs;
285         unsigned long *next_bp;
286 
287         if (unwind_done(state))
288                 return false;
289 
290         /* Have we reached the end? */
291         if (state->regs && user_mode(state->regs))
292                 goto the_end;
293 
294         if (is_last_task_frame(state)) {
295                 regs = task_pt_regs(state->task);
296 
297                 /*
298                  * kthreads (other than the boot CPU's idle thread) have some
299                  * partial regs at the end of their stack which were placed
300                  * there by copy_thread_tls().  But the regs don't have any
301                  * useful information, so we can skip them.
302                  *
303                  * This user_mode() check is slightly broader than a PF_KTHREAD
304                  * check because it also catches the awkward situation where a
305                  * newly forked kthread transitions into a user task by calling
306                  * do_execve(), which eventually clears PF_KTHREAD.
307                  */
308                 if (!user_mode(regs))
309                         goto the_end;
310 
311                 /*
312                  * We're almost at the end, but not quite: there's still the
313                  * syscall regs frame.  Entry code doesn't encode the regs
314                  * pointer for syscalls, so we have to set it manually.
315                  */
316                 state->regs = regs;
317                 state->bp = NULL;
318                 state->ip = 0;
319                 return true;
320         }
321 
322         /* Get the next frame pointer: */
323         if (state->regs)
324                 next_bp = (unsigned long *)state->regs->bp;
325         else
326                 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
327 
328         /* Move to the next frame if it's safe: */
329         if (!update_stack_state(state, next_bp))
330                 goto bad_address;
331 
332         return true;
333 
334 bad_address:
335         state->error = true;
336 
337         /*
338          * When unwinding a non-current task, the task might actually be
339          * running on another CPU, in which case it could be modifying its
340          * stack while we're reading it.  This is generally not a problem and
341          * can be ignored as long as the caller understands that unwinding
342          * another task will not always succeed.
343          */
344         if (state->task != current)
345                 goto the_end;
346 
347         /*
348          * Don't warn if the unwinder got lost due to an interrupt in entry
349          * code or in the C handler before the first frame pointer got set up:
350          */
351         if (state->got_irq && in_entry_code(state->ip))
352                 goto the_end;
353         if (state->regs &&
354             state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
355             state->regs->sp < (unsigned long)task_pt_regs(state->task))
356                 goto the_end;
357 
358         /*
359          * There are some known frame pointer issues on 32-bit.  Disable
360          * unwinder warnings on 32-bit until it gets objtool support.
361          */
362         if (IS_ENABLED(CONFIG_X86_32))
363                 goto the_end;
364 
365         if (state->regs) {
366                 printk_deferred_once(KERN_WARNING
367                         "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
368                         state->regs, state->task->comm,
369                         state->task->pid, next_bp);
370                 unwind_dump(state);
371         } else {
372                 printk_deferred_once(KERN_WARNING
373                         "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
374                         state->bp, state->task->comm,
375                         state->task->pid, next_bp);
376                 unwind_dump(state);
377         }
378 the_end:
379         state->stack_info.type = STACK_TYPE_UNKNOWN;
380         return false;
381 }
382 EXPORT_SYMBOL_GPL(unwind_next_frame);
383 
384 void __unwind_start(struct unwind_state *state, struct task_struct *task,
385                     struct pt_regs *regs, unsigned long *first_frame)
386 {
387         unsigned long *bp;
388 
389         memset(state, 0, sizeof(*state));
390         state->task = task;
391         state->got_irq = (regs);
392 
393         /* Don't even attempt to start from user mode regs: */
394         if (regs && user_mode(regs)) {
395                 state->stack_info.type = STACK_TYPE_UNKNOWN;
396                 return;
397         }
398 
399         bp = get_frame_pointer(task, regs);
400 
401         /* Initialize stack info and make sure the frame data is accessible: */
402         get_stack_info(bp, state->task, &state->stack_info,
403                        &state->stack_mask);
404         update_stack_state(state, bp);
405 
406         /*
407          * The caller can provide the address of the first frame directly
408          * (first_frame) or indirectly (regs->sp) to indicate which stack frame
409          * to start unwinding at.  Skip ahead until we reach it.
410          */
411         while (!unwind_done(state) &&
412                (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
413                         state->bp < first_frame))
414                 unwind_next_frame(state);
415 }
416 EXPORT_SYMBOL_GPL(__unwind_start);
417 

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