From 87a342f5db69d53ea70493bb1ec69c9047677038 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Fri, 7 Aug 2009 10:33:43 +0800 Subject: [PATCH] tracing/filters: Support filtering for char * strings 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) ... ) ... ); The filtering will not dereference "char *" unless the developer explicitly sets FILTER_PTR_STR in __field_ext. Signed-off-by: Li Zefan LKML-Reference: <4A7B9287.90205@cn.fujitsu.com> Signed-off-by: Steven Rostedt --- 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 0440bea8f6bb..ace2da9e0a0d 100644 --- a/include/linux/ftrace_event.h +++ b/include/linux/ftrace_event.h @@ -144,6 +144,7 @@ enum { FILTER_OTHER = 0, FILTER_STATIC_STRING, FILTER_DYN_STRING, + FILTER_PTR_STRING, }; extern int trace_define_field(struct ftrace_event_call *call, diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c index 8a8e576733fc..9f03082c81d8 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); + } } else { if (field->is_signed) ret = strict_strtoll(pred->str_val, 0, &val); -- GitLab