Re: [PATCH] tracepoint: Do not fail unregistering a probe due to memory allocation

Steven Rostedt
2020-11-17T22:19:29Z

On Tue, 17 Nov 2020 13:33:42 -0800
Kees Cook <keescook@chromium.org> wrote:

> As I think got discussed in the thread, what you had here wouldn't work
> in a CFI build if the function prototype of the call site and the
> function don't match. (Though I can't tell if .func() is ever called?)
>
> i.e. .func's prototype must match tp_stub_func()'s.
>

Hmm, I wonder how you handle tracepoints? This is called here:

include/linux/tracepoint.h:

#define DEFINE_TRACE_FN(_name, _reg, _unreg, proto, args) \
static const char __tpstrtab_##_name[] \
__section("__tracepoints_strings") = #_name; \
extern struct static_call_key STATIC_CALL_KEY(tp_func_##_name); \
int __traceiter_##_name(void *__data, proto); \
struct tracepoint __tracepoint_##_name __used \
__section("__tracepoints") = { \
.name = __tpstrtab_##_name, \
.key = STATIC_KEY_INIT_FALSE, \
.static_call_key = &STATIC_CALL_KEY(tp_func_##_name), \
.static_call_tramp = STATIC_CALL_TRAMP_ADDR(tp_func_##_name), \
.iterator = &__traceiter_##_name, \
.regfunc = _reg, \
.unregfunc = _unreg, \
.funcs = NULL }; \
__TRACEPOINT_ENTRY(_name); \
int __traceiter_##_name(void *__data, proto) \
{ \
struct tracepoint_func *it_func_ptr; \
void *it_func; \
\
it_func_ptr = \
rcu_dereference_raw((&__tracepoint_##_name)->funcs); \
do { \
it_func = (it_func_ptr)->func; \
__data = (it_func_ptr)->data; \

((void(*)(void *, proto))(it_func))(__data, args); \

^^^^ called above ^^^^

Where args is unique for every tracepoint, but func is simply a void
pointer.

-- Steve

} while ((++it_func_ptr)->func); \
return 0; \
} \