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tracing: Show real address for trace event arguments

To help debugging kernel, show real address for trace event arguments in tracefs/trace{,pipe} instead of hashed pointer value. Since ftrace human-readable format uses vsprintf(), all %p are translated to hash values instead of pointer address. However, when debugging the kernel, raw address value gives a hint when comparing with the memory mapping in the kernel. (Those are sometimes used with crash log, which is not hashed too) So converting %p with %px when calling trace_seq_printf(). Moreover, this is not improving the security because the tracefs can be used only by root user and the raw address values are readable from tracefs/percpu/cpu*/trace_pipe_raw file. Link: https://lkml.kernel.org/r/160277370703.29307.5134475491761971203.stgit@devnote2

Masami Hiramatsu committed 6 years ago

Commit efbbdaa1 parent 7d536755 files · +88 −3Browse files

Showing the changes to kernel/trace (3 of 5 files). Show all

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3 files
  1. kernel/trace/trace.c +70 −1
  2. kernel/trace/trace.h +2 −0
  3. kernel/trace/trace_output.c +11 −1
kernel/trace/trace.c+70−1
@@ -3530,6 +3530,62 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu, · 3529 unmodified lines
3530 return next;3530 return next;
3531}3531}
3532 3532
3533#define STATIC_FMT_BUF_SIZE 128
3534static char static_fmt_buf[STATIC_FMT_BUF_SIZE];
3535
3536static char *trace_iter_expand_format(struct trace_iterator *iter)
3537{
3538 char *tmp;
3539
3540 if (iter->fmt == static_fmt_buf)
3541 return NULL;
3542
3543 tmp = krealloc(iter->fmt, iter->fmt_size + STATIC_FMT_BUF_SIZE,
3544 GFP_KERNEL);
3545 if (tmp) {
3546 iter->fmt_size += STATIC_FMT_BUF_SIZE;
3547 iter->fmt = tmp;
3548 }
3549
3550 return tmp;
3551}
3552
3553const char *trace_event_format(struct trace_iterator *iter, const char *fmt)
3554{
3555 const char *p, *new_fmt;
3556 char *q;
3557
3558 if (WARN_ON_ONCE(!fmt))
3559 return fmt;
3560
3561 p = fmt;
3562 new_fmt = q = iter->fmt;
3563 while (*p) {
3564 if (unlikely(q - new_fmt + 3 > iter->fmt_size)) {
3565 if (!trace_iter_expand_format(iter))
3566 return fmt;
3567
3568 q += iter->fmt - new_fmt;
3569 new_fmt = iter->fmt;
3570 }
3571
3572 *q++ = *p++;
3573
3574 /* Replace %p with %px */
3575 if (p[-1] == '%') {
3576 if (p[0] == '%') {
3577 *q++ = *p++;
3578 } else if (p[0] == 'p' && !isalnum(p[1])) {
3579 *q++ = *p++;
3580 *q++ = 'x';
3581 }
3582 }
3583 }
3584 *q = '\0';
3585
3586 return new_fmt;
3587}
3588
3533#define STATIC_TEMP_BUF_SIZE 1283589#define STATIC_TEMP_BUF_SIZE 128
3534static char static_temp_buf[STATIC_TEMP_BUF_SIZE] __aligned(4);3590static char static_temp_buf[STATIC_TEMP_BUF_SIZE] __aligned(4);
3535 3591
@@ -4322,6 +4378,16 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) · 786 unmodified lines
4322 if (iter->temp)4378 if (iter->temp)
4323 iter->temp_size = 128;4379 iter->temp_size = 128;
4324 4380
4381 /*
4382 * trace_event_printf() may need to modify given format
4383 * string to replace %p with %px so that it shows real address
4384 * instead of hash value. However, that is only for the event
4385 * tracing, other tracer may not need. Defer the allocation
4386 * until it is needed.
4387 */
4388 iter->fmt = NULL;
4389 iter->fmt_size = 0;
4390
4325 /*4391 /*
4326 * We make a copy of the current tracer to avoid concurrent4392 * We make a copy of the current tracer to avoid concurrent
4327 * changes on it while we are reading.4393 * changes on it while we are reading.
@@ -4473,6 +4539,7 @@ static int tracing_release(struct inode *inode, struct file *file) · 145 unmodified lines
4473 4539
4474 mutex_destroy(&iter->mutex);4540 mutex_destroy(&iter->mutex);
4475 free_cpumask_var(iter->started);4541 free_cpumask_var(iter->started);
4542 kfree(iter->fmt);
4476 kfree(iter->temp);4543 kfree(iter->temp);
4477 kfree(iter->trace);4544 kfree(iter->trace);
4478 kfree(iter->buffer_iter);4545 kfree(iter->buffer_iter);
@@ -9331,9 +9398,11 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) · 4852 unmodified lines
9331 9398
9332 /* Simulate the iterator */9399 /* Simulate the iterator */
9333 trace_init_global_iter(&iter);9400 trace_init_global_iter(&iter);
9334 /* Can not use kmalloc for iter.temp */9401 /* Can not use kmalloc for iter.temp and iter.fmt */
9335 iter.temp = static_temp_buf;9402 iter.temp = static_temp_buf;
9336 iter.temp_size = STATIC_TEMP_BUF_SIZE;9403 iter.temp_size = STATIC_TEMP_BUF_SIZE;
9404 iter.fmt = static_fmt_buf;
9405 iter.fmt_size = STATIC_FMT_BUF_SIZE;
9337 9406
9338 for_each_tracing_cpu(cpu) {9407 for_each_tracing_cpu(cpu) {
9339 atomic_inc(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);9408 atomic_inc(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);
kernel/trace/trace.h+2−0
@@ -581,6 +581,8 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter, · 580 unmodified lines
581void trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,581void trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,
582 struct ring_buffer_event *event);582 struct ring_buffer_event *event);
583 583
584const char *trace_event_format(struct trace_iterator *iter, const char *fmt);
585
584int trace_empty(struct trace_iterator *iter);586int trace_empty(struct trace_iterator *iter);
585 587
586void *trace_find_next_entry_inc(struct trace_iterator *iter);588void *trace_find_next_entry_inc(struct trace_iterator *iter);
kernel/trace/trace_output.c+11−1
@@ -312,13 +312,23 @@ int trace_raw_output_prep(struct trace_iterator *iter, · 311 unmodified lines
312}312}
313EXPORT_SYMBOL(trace_raw_output_prep);313EXPORT_SYMBOL(trace_raw_output_prep);
314 314
315void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...)
316{
317 va_list ap;
318
319 va_start(ap, fmt);
320 trace_seq_vprintf(&iter->seq, trace_event_format(iter, fmt), ap);
321 va_end(ap);
322}
323EXPORT_SYMBOL(trace_event_printf);
324
315static int trace_output_raw(struct trace_iterator *iter, char *name,325static int trace_output_raw(struct trace_iterator *iter, char *name,
316 char *fmt, va_list ap)326 char *fmt, va_list ap)
317{327{
318 struct trace_seq *s = &iter->seq;328 struct trace_seq *s = &iter->seq;
319 329
320 trace_seq_printf(s, "%s: ", name);330 trace_seq_printf(s, "%s: ", name);
321 trace_seq_vprintf(s, fmt, ap);331 trace_seq_vprintf(s, trace_event_format(iter, fmt), ap);
322 332
323 return trace_handle_return(s);333 return trace_handle_return(s);
324}334}