Messages in this thread | | | Date | Thu, 6 Aug 2009 10:21:45 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 3/3] tracing/filters: Support filtering for char * strings |
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On Thu, 6 Aug 2009, Li Zefan wrote:
> Usually, char * entries are dangerous in traces because the string > can be released whereas a pointer to it can still wait to be read from > the ring buffer. > > But sometimes we can assume it's safe, like in case of RO data > (eg: __file__ or __line__, used in bkl trace event). If these RO data > are in a module and so is the call to the trace event, then it's safe, > because the ring buffer will be flushed once this module get unloaded. > > To allow char * to be treated as a string: > > TRACE_EVENT(..., > > TP_STRUCT__entry( > __field_ext(const char *, name, FILTER_PTR_STRING) > ... > ) > > ... > ); > > Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> > --- > include/linux/ftrace_event.h | 1 + > kernel/trace/trace_events_filter.c | 26 +++++++++++++++++++++++--- > 2 files changed, 24 insertions(+), 3 deletions(-) > > diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h > index 14c388e..1a98a61 100644 > --- a/include/linux/ftrace_event.h > +++ b/include/linux/ftrace_event.h > @@ -141,6 +141,7 @@ extern int filter_current_check_discard(struct ftrace_event_call *call, > enum { > FILTER_STATIC_STRING = 1, > FILTER_DYN_STRING, > + FILTER_PTR_STRING, > FILTER_OTHER, > }; > > diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c > index 5e7f031..b16923e 100644 > --- a/kernel/trace/trace_events_filter.c > +++ b/kernel/trace/trace_events_filter.c > @@ -163,6 +163,20 @@ static int filter_pred_string(struct filter_pred *pred, void *event, > return match; > } > > +/* Filter predicate for char * pointers */ > +static int filter_pred_pchar(struct filter_pred *pred, void *event, > + int val1, int val2) > +{ > + char **addr = (char **)(event + pred->offset); > + int cmp, match; > + > + cmp = strncmp(*addr, pred->str_val, pred->str_len); > + > + match = (!cmp) ^ pred->not; > + > + return match; > +} > + > /* > * Filter predicate for dynamic sized arrays of characters. > * These are implemented through a list of strings at the end > @@ -489,7 +503,8 @@ int filter_assign_type(const char *type) > static bool is_string_field(struct ftrace_event_field *field) > { > return field->filter_type == FILTER_DYN_STRING || > - field->filter_type == FILTER_STATIC_STRING; > + field->filter_type == FILTER_STATIC_STRING || > + field->filter_type == FILTER_PTR_STRING; > } > > static int is_legal_op(struct ftrace_event_field *field, int op) > @@ -579,11 +594,16 @@ static int filter_add_pred(struct filter_parse_state *ps, > } > > if (is_string_field(field)) { > + pred->str_len = field->size; > + > if (field->filter_type == FILTER_STATIC_STRING) > fn = filter_pred_string; > - else > + else if (field->filter_type == FILTER_DYN_STRING) > fn = filter_pred_strloc; > - pred->str_len = field->size; > + else { > + fn = filter_pred_pchar; > + pred->str_len = strlen(pred->str_val); > + }
I'm a little dense here, where do we protect against someone making a tracepoint that points to unsafe data?
-- Steve
> } else { > if (field->is_signed) > ret = strict_strtoll(pred->str_val, 0, &val); > -- > 1.6.3 > >
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