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Message-ID: <20201117171904.2d455699@gandalf.local.home>
Date: Tue, 17 Nov 2020 17:19:04 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Kees Cook <keescook@...omium.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Matt Mullins <mmullins@...x.us>,
Ingo Molnar <mingo@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Dmitry Vyukov <dvyukov@...gle.com>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Andrii Nakryiko <andriin@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>,
netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] tracepoint: Do not fail unregistering a probe due to
memory allocation
On Tue, 17 Nov 2020 13:33:42 -0800
Kees Cook <keescook@...omium.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; \
} \
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