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Date: Thu, 23 Mar 2023 08:53:21 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-kernel@...r.kernel.org, mhiramat@...nel.org,
"Jose E. Marchesi" <jose.marchesi@...cle.com>,
Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] tracepoint: Fix CFI failures with tp_stub_func
On Thu, 23 Mar 2023 11:40:12 +0000
Mark Rutland <mark.rutland@....com> wrote:
> When CLANG_CFI is in use, using tracing will occasionally result in
> CFI failures, e.g.
>
> | CFI failure at syscall_trace_enter+0x66c/0x7d0 (target: tp_stub_func+0x0/0x2c; expected type: 0x4877830c)
> | Internal error: Oops - CFI: 00000000f200823a [#1] PREEMPT SMP
> | CPU: 2 PID: 118 Comm: klogd Not tainted 6.3.0-rc3-00002-gc242ea6f2f98 #2
> | Hardware name: linux,dummy-virt (DT)
> | pstate: 30400005 (nzCV daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> | pc : syscall_trace_enter+0x66c/0x7d0
> | lr : syscall_trace_enter+0x5e8/0x7d0
> | sp : ffff800015ce7d80
> | x29: ffff800015ce7d80 x28: ffff000017538000 x27: 0000000000000003
> | x26: ffff8000084c9454 x25: ffff00001182bd10 x24: dfff800000000000
> | x23: 1fffe00002ea7001 x22: ffff00001182bd10 x21: ffff000017538008
> | x20: ffff000017538000 x19: ffff800015ce7eb0 x18: 0000000000000000
> | x17: 000000004877830c x16: 00000000a540670c x15: 0000000000000000
> | x14: 0000000000000000 x13: 0000000000000000 x12: ff80800008039d8c
> | x11: ff80800008039dd0 x10: 0000000000000000 x9 : 0000000000000000
> | x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
> | x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
> | x2 : 00000000000000ce x1 : ffff800015ce7eb0 x0 : ffff800013d55000
> | Call trace:
> | syscall_trace_enter+0x66c/0x7d0
> | el0_svc_common+0x1dc/0x268
> | do_el0_svc+0x70/0x1a4
> | el0_svc+0x58/0x14c
> | el0t_64_sync_handler+0x84/0xf0
> | el0t_64_sync+0x190/0x194
> | Code: 72906191 72a90ef1 6b11021f 54000040 (d4304740)
> | ---[ end trace 0000000000000000 ]---
>
> This happens because the function prototype of tp_sub_func doesn't match
> the prototype of the tracepoint function. As each tracepoint may have a
> distinct prototype, it's not possible to share a common stub function.
I hate C!
>
> Avoid this by creating a stub function for each tracepoint with the
> correct prototype, and using these rather than tp_stub_func.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org
> ---
> include/linux/tracepoint-defs.h | 1 +
> include/linux/tracepoint.h | 5 +++++
> kernel/tracepoint.c | 31 ++++++++++++++-----------------
> 3 files changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index e7c2276be33eb..a306ac7255220 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -35,6 +35,7 @@ struct tracepoint {
> struct static_call_key *static_call_key;
> void *static_call_tramp;
> void *iterator;
> + void *stub;
> int (*regfunc)(void);
> void (*unregfunc)(void);
> struct tracepoint_func __rcu *funcs;
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 6811e43c1b5c2..1640926441910 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -303,6 +303,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> __section("__tracepoints_strings") = #_name; \
> extern struct static_call_key STATIC_CALL_KEY(tp_func_##_name); \
> int __traceiter_##_name(void *__data, proto); \
> + void __tracestub_##_name(void *, proto); \
> struct tracepoint __tracepoint_##_name __used \
> __section("__tracepoints") = { \
> .name = __tpstrtab_##_name, \
> @@ -310,6 +311,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> .static_call_key = &STATIC_CALL_KEY(tp_func_##_name), \
> .static_call_tramp = STATIC_CALL_TRAMP_ADDR(tp_func_##_name), \
> .iterator = &__traceiter_##_name, \
> + .stub = &__tracestub_##_name, \
> .regfunc = _reg, \
> .unregfunc = _unreg, \
> .funcs = NULL }; \
> @@ -330,6 +332,9 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> } \
> return 0; \
> } \
> + void __tracestub_##_name(void *__data, proto) \
> + { \
> + } \
I purposely did not do this because this adds over a thousand stub
functions! It adds one for *every* tracepoint (and that is a superset of
trace events).
Is there some other way we could do this?
C really really needs a way to make a generic void do_nothing(...) function!
I added some compiler folks to the Cc to hear our grievances.
-- Steve
> DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
>
> #define DEFINE_TRACE(name, proto, args) \
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 8d1507dd07246..d9186629a0095 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -98,12 +98,6 @@ struct tp_probes {
> struct tracepoint_func probes[];
> };
>
> -/* Called in removal of a func but failed to allocate a new tp_funcs */
> -static void tp_stub_func(void)
> -{
> - return;
> -}
> -
> static inline void *allocate_probes(int count)
> {
> struct tp_probes *p = kmalloc(struct_size(p, probes, count),
> @@ -177,13 +171,15 @@ static void debug_print_probes(struct tracepoint_func *funcs)
> }
>
> static struct tracepoint_func *
> -func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
> +func_add(struct tracepoint *tp, struct tracepoint_func **funcs,
> + struct tracepoint_func *tp_func,
> int prio)
> {
> struct tracepoint_func *old, *new;
> int iter_probes; /* Iterate over old probe array. */
> int nr_probes = 0; /* Counter for probes */
> int pos = -1; /* Insertion position into new array */
> + void *stub_func = tp->stub;
>
> if (WARN_ON(!tp_func->func))
> return ERR_PTR(-EINVAL);
> @@ -193,7 +189,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
> if (old) {
> /* (N -> N+1), (N != 0, 1) probes */
> for (iter_probes = 0; old[iter_probes].func; iter_probes++) {
> - if (old[iter_probes].func == tp_stub_func)
> + if (old[iter_probes].func == stub_func)
> continue; /* Skip stub functions. */
> if (old[iter_probes].func == tp_func->func &&
> old[iter_probes].data == tp_func->data)
> @@ -208,7 +204,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
> if (old) {
> nr_probes = 0;
> for (iter_probes = 0; old[iter_probes].func; iter_probes++) {
> - if (old[iter_probes].func == tp_stub_func)
> + if (old[iter_probes].func == stub_func)
> continue;
> /* Insert before probes of lower priority */
> if (pos < 0 && old[iter_probes].prio < prio)
> @@ -229,11 +225,12 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
> return old;
> }
>
> -static void *func_remove(struct tracepoint_func **funcs,
> - struct tracepoint_func *tp_func)
> +static void *func_remove(struct tracepoint *tp, struct tracepoint_func **funcs,
> + struct tracepoint_func *tp_func)
> {
> int nr_probes = 0, nr_del = 0, i;
> struct tracepoint_func *old, *new;
> + void *stub_func = tp->stub;
>
> old = *funcs;
>
> @@ -246,7 +243,7 @@ static void *func_remove(struct tracepoint_func **funcs,
> for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> if ((old[nr_probes].func == tp_func->func &&
> old[nr_probes].data == tp_func->data) ||
> - old[nr_probes].func == tp_stub_func)
> + old[nr_probes].func == stub_func)
> nr_del++;
> }
> }
> @@ -269,7 +266,7 @@ static void *func_remove(struct tracepoint_func **funcs,
> for (i = 0; old[i].func; i++) {
> if ((old[i].func != tp_func->func ||
> old[i].data != tp_func->data) &&
> - old[i].func != tp_stub_func)
> + old[i].func != stub_func)
> new[j++] = old[i];
> }
> new[nr_probes - nr_del].func = NULL;
> @@ -277,12 +274,12 @@ static void *func_remove(struct tracepoint_func **funcs,
> } else {
> /*
> * Failed to allocate, replace the old function
> - * with calls to tp_stub_func.
> + * with calls to stub_func.
> */
> for (i = 0; old[i].func; i++) {
> if (old[i].func == tp_func->func &&
> old[i].data == tp_func->data)
> - WRITE_ONCE(old[i].func, tp_stub_func);
> + WRITE_ONCE(old[i].func, stub_func);
> }
> *funcs = old;
> }
> @@ -335,7 +332,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
>
> tp_funcs = rcu_dereference_protected(tp->funcs,
> lockdep_is_held(&tracepoints_mutex));
> - old = func_add(&tp_funcs, func, prio);
> + old = func_add(tp, &tp_funcs, func, prio);
> if (IS_ERR(old)) {
> WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
> return PTR_ERR(old);
> @@ -400,7 +397,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
>
> tp_funcs = rcu_dereference_protected(tp->funcs,
> lockdep_is_held(&tracepoints_mutex));
> - old = func_remove(&tp_funcs, func);
> + old = func_remove(tp, &tp_funcs, func);
> if (WARN_ON_ONCE(IS_ERR(old)))
> return PTR_ERR(old);
>
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