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

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu 2020-10-15 23:55:07 +09:00 committed by Steven Rostedt (VMware)
parent 7d5367539a
commit efbbdaa22b
5 changed files with 88 additions and 3 deletions

View File

@ -55,6 +55,8 @@ struct trace_event;
int trace_raw_output_prep(struct trace_iterator *iter,
struct trace_event *event);
extern __printf(2, 3)
void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...);
/*
* The trace entry - the most basic unit of tracing. This is what
@ -87,6 +89,8 @@ struct trace_iterator {
unsigned long iter_flags;
void *temp; /* temp holder */
unsigned int temp_size;
char *fmt; /* modified format holder */
unsigned int fmt_size;
/* trace_seq for __print_flags() and __print_symbolic() etc. */
struct trace_seq tmp_seq;

View File

@ -364,7 +364,7 @@ trace_raw_output_##call(struct trace_iterator *iter, int flags, \
if (ret != TRACE_TYPE_HANDLED) \
return ret; \
\
trace_seq_printf(s, print); \
trace_event_printf(iter, print); \
\
return trace_handle_return(s); \
} \

View File

@ -3530,6 +3530,62 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu,
return next;
}
#define STATIC_FMT_BUF_SIZE 128
static char static_fmt_buf[STATIC_FMT_BUF_SIZE];
static char *trace_iter_expand_format(struct trace_iterator *iter)
{
char *tmp;
if (iter->fmt == static_fmt_buf)
return NULL;
tmp = krealloc(iter->fmt, iter->fmt_size + STATIC_FMT_BUF_SIZE,
GFP_KERNEL);
if (tmp) {
iter->fmt_size += STATIC_FMT_BUF_SIZE;
iter->fmt = tmp;
}
return tmp;
}
const char *trace_event_format(struct trace_iterator *iter, const char *fmt)
{
const char *p, *new_fmt;
char *q;
if (WARN_ON_ONCE(!fmt))
return fmt;
p = fmt;
new_fmt = q = iter->fmt;
while (*p) {
if (unlikely(q - new_fmt + 3 > iter->fmt_size)) {
if (!trace_iter_expand_format(iter))
return fmt;
q += iter->fmt - new_fmt;
new_fmt = iter->fmt;
}
*q++ = *p++;
/* Replace %p with %px */
if (p[-1] == '%') {
if (p[0] == '%') {
*q++ = *p++;
} else if (p[0] == 'p' && !isalnum(p[1])) {
*q++ = *p++;
*q++ = 'x';
}
}
}
*q = '\0';
return new_fmt;
}
#define STATIC_TEMP_BUF_SIZE 128
static char static_temp_buf[STATIC_TEMP_BUF_SIZE] __aligned(4);
@ -4322,6 +4378,16 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
if (iter->temp)
iter->temp_size = 128;
/*
* trace_event_printf() may need to modify given format
* string to replace %p with %px so that it shows real address
* instead of hash value. However, that is only for the event
* tracing, other tracer may not need. Defer the allocation
* until it is needed.
*/
iter->fmt = NULL;
iter->fmt_size = 0;
/*
* We make a copy of the current tracer to avoid concurrent
* changes on it while we are reading.
@ -4473,6 +4539,7 @@ static int tracing_release(struct inode *inode, struct file *file)
mutex_destroy(&iter->mutex);
free_cpumask_var(iter->started);
kfree(iter->fmt);
kfree(iter->temp);
kfree(iter->trace);
kfree(iter->buffer_iter);
@ -9331,9 +9398,11 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
/* Simulate the iterator */
trace_init_global_iter(&iter);
/* Can not use kmalloc for iter.temp */
/* Can not use kmalloc for iter.temp and iter.fmt */
iter.temp = static_temp_buf;
iter.temp_size = STATIC_TEMP_BUF_SIZE;
iter.fmt = static_fmt_buf;
iter.fmt_size = STATIC_FMT_BUF_SIZE;
for_each_tracing_cpu(cpu) {
atomic_inc(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);

View File

@ -581,6 +581,8 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
void trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,
struct ring_buffer_event *event);
const char *trace_event_format(struct trace_iterator *iter, const char *fmt);
int trace_empty(struct trace_iterator *iter);
void *trace_find_next_entry_inc(struct trace_iterator *iter);

View File

@ -312,13 +312,23 @@ int trace_raw_output_prep(struct trace_iterator *iter,
}
EXPORT_SYMBOL(trace_raw_output_prep);
void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
trace_seq_vprintf(&iter->seq, trace_event_format(iter, fmt), ap);
va_end(ap);
}
EXPORT_SYMBOL(trace_event_printf);
static int trace_output_raw(struct trace_iterator *iter, char *name,
char *fmt, va_list ap)
{
struct trace_seq *s = &iter->seq;
trace_seq_printf(s, "%s: ", name);
trace_seq_vprintf(s, fmt, ap);
trace_seq_vprintf(s, trace_event_format(iter, fmt), ap);
return trace_handle_return(s);
}