tracing/probes: Add string type check with BTF

Add a string type checking with BTF information if possible.
This will check whether the given BTF argument (and field) is
signed char array or pointer to signed char. If not, it reject
the 'string' type. If it is pointer to signed char, it adds
a dereference opration so that it can correctly fetch the
string data from memory.

 # echo 'f getname_flags%return retval->name:string' >> dynamic_events
 # echo 't sched_switch next->comm:string' >> dynamic_events

The above cases, 'struct filename::name' is 'char *' and
'struct task_struct::comm' is 'char []'. But in both case,
user can specify ':string' to fetch the string data.

Link: https://lore.kernel.org/all/169272159250.160970.1881112937198526188.stgit@devnote2/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 7345e1af4db235cefbc3b8c6e82a21f4e883d801..4dc74d73fc1df5af9ee297611865705d44259663 100644 (file)
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -310,6 +310,77 @@ static u32 btf_type_int(const struct btf_type *t)
        return *(u32 *)(t + 1);
 }
 
+static bool btf_type_is_char_ptr(struct btf *btf, const struct btf_type *type)
+{
+       const struct btf_type *real_type;
+       u32 intdata;
+       s32 tid;
+
+       real_type = btf_type_skip_modifiers(btf, type->type, &tid);
+       if (!real_type)
+               return false;
+
+       if (BTF_INFO_KIND(real_type->info) != BTF_KIND_INT)
+               return false;
+
+       intdata = btf_type_int(real_type);
+       return !(BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED)
+               && BTF_INT_BITS(intdata) == 8;
+}
+
+static bool btf_type_is_char_array(struct btf *btf, const struct btf_type *type)
+{
+       const struct btf_type *real_type;
+       const struct btf_array *array;
+       u32 intdata;
+       s32 tid;
+
+       if (BTF_INFO_KIND(type->info) != BTF_KIND_ARRAY)
+               return false;
+
+       array = (const struct btf_array *)(type + 1);
+
+       real_type = btf_type_skip_modifiers(btf, array->type, &tid);
+
+       intdata = btf_type_int(real_type);
+       return !(BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED)
+               && BTF_INT_BITS(intdata) == 8;
+}
+
+static int check_prepare_btf_string_fetch(char *typename,
+                               struct fetch_insn **pcode,
+                               struct traceprobe_parse_context *ctx)
+{
+       struct btf *btf = ctx->btf;
+
+       if (!btf || !ctx->last_type)
+               return 0;
+
+       /* char [] does not need any change. */
+       if (btf_type_is_char_array(btf, ctx->last_type))
+               return 0;
+
+       /* char * requires dereference the pointer. */
+       if (btf_type_is_char_ptr(btf, ctx->last_type)) {
+               struct fetch_insn *code = *pcode + 1;
+
+               if (code->op == FETCH_OP_END) {
+                       trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
+                       return -E2BIG;
+               }
+               if (typename[0] == 'u')
+                       code->op = FETCH_OP_UDEREF;
+               else
+                       code->op = FETCH_OP_DEREF;
+               code->offset = 0;
+               *pcode = code;
+               return 0;
+       }
+       /* Other types are not available for string */
+       trace_probe_log_err(ctx->offset, BAD_TYPE4STR);
+       return -EINVAL;
+}
+
 static const char *fetch_type_from_btf_type(struct btf *btf,
                                        const struct btf_type *type,
                                        struct traceprobe_parse_context *ctx)
@@ -675,6 +746,13 @@ static int parse_btf_bitfield(struct fetch_insn **pcode,
 #define find_fetch_type_from_btf_type(ctx)             \
        find_fetch_type(NULL, ctx->flags)
 
+static int check_prepare_btf_string_fetch(char *typename,
+                               struct fetch_insn **pcode,
+                               struct traceprobe_parse_context *ctx)
+{
+       return 0;
+}
+
 #endif
 
 #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
@@ -1117,8 +1195,15 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 
        /* Update storing type if BTF is available */
        if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
-           !t && ctx->last_type)
-               parg->type = find_fetch_type_from_btf_type(ctx);
+           ctx->last_type) {
+               if (!t) {
+                       parg->type = find_fetch_type_from_btf_type(ctx);
+               } else if (strstr(t, "string")) {
+                       ret = check_prepare_btf_string_fetch(t, &code, ctx);
+                       if (ret)
+                               goto fail;
+               }
+       }
 
        ret = -EINVAL;
        /* Store operation */

diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 9184c84833f8db38b8374cc48cf6e7d5af01d667..7f929482e8d43e97d9704b0c39c7d8841b98529b 100644 (file)
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -513,7 +513,8 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
        C(NOSUP_DAT_ARG,        "Non pointer structure/union argument is not supported."),\
        C(BAD_HYPHEN,           "Failed to parse single hyphen. Forgot '>'?"),  \
        C(NO_BTF_FIELD,         "This field is not found."),    \
-       C(BAD_BTF_TID,          "Failed to get BTF type info."),
+       C(BAD_BTF_TID,          "Failed to get BTF type info."),\
+       C(BAD_TYPE4STR,         "This type does not fit for string."),
 
 #undef C
 #define C(a, b)                TP_ERR_##a