We need to extend the bpf_timer API, but the way forward relies on kfuncs.
So make bpf_timer known for kfuncs from the verifier PoV
Signed-off-by: Benjamin Tissoires <[email protected]>
---
changes in v4:
- enforce KF_ARG_PTR_TO_TIMER to be of type PTR_TO_MAP_VALUE
new in v3 (split from v2 02/10)
---
kernel/bpf/verifier.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 63749ad5ac6b..1483ebc0ee73 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10826,6 +10826,7 @@ enum {
KF_ARG_LIST_NODE_ID,
KF_ARG_RB_ROOT_ID,
KF_ARG_RB_NODE_ID,
+ KF_ARG_TIMER_ID,
};
BTF_ID_LIST(kf_arg_btf_ids)
@@ -10834,6 +10835,7 @@ BTF_ID(struct, bpf_list_head)
BTF_ID(struct, bpf_list_node)
BTF_ID(struct, bpf_rb_root)
BTF_ID(struct, bpf_rb_node)
+BTF_ID(struct, bpf_timer_kern)
static bool __is_kfunc_ptr_arg_type(const struct btf *btf,
const struct btf_param *arg, int type)
@@ -10877,6 +10879,12 @@ static bool is_kfunc_arg_rbtree_node(const struct btf *btf, const struct btf_par
return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RB_NODE_ID);
}
+static bool is_kfunc_arg_timer(const struct btf *btf, const struct btf_param *arg)
+{
+ bool ret = __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_TIMER_ID);
+ return ret;
+}
+
static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf,
const struct btf_param *arg)
{
@@ -10946,6 +10954,7 @@ enum kfunc_ptr_arg_type {
KF_ARG_PTR_TO_NULL,
KF_ARG_PTR_TO_CONST_STR,
KF_ARG_PTR_TO_MAP,
+ KF_ARG_PTR_TO_TIMER,
};
enum special_kfunc_type {
@@ -11102,6 +11111,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
if (is_kfunc_arg_map(meta->btf, &args[argno]))
return KF_ARG_PTR_TO_MAP;
+ if (is_kfunc_arg_timer(meta->btf, &args[argno]))
+ return KF_ARG_PTR_TO_TIMER;
+
if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
if (!btf_type_is_struct(ref_t)) {
verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
@@ -11735,6 +11747,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
case KF_ARG_PTR_TO_CALLBACK:
case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
case KF_ARG_PTR_TO_CONST_STR:
+ case KF_ARG_PTR_TO_TIMER:
/* Trusted by default */
break;
default:
@@ -12021,6 +12034,12 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
if (ret)
return ret;
break;
+ case KF_ARG_PTR_TO_TIMER:
+ if (reg->type != PTR_TO_MAP_VALUE) {
+ verbose(env, "arg#%d doesn't point to a map value\n", i);
+ return -EINVAL;
+ }
+ break;
}
}
--
2.44.0
On Mon, Mar 18, 2024 at 10:59 PM Eduard Zingerman <[email protected]> wrote:
>
> On Fri, 2024-03-15 at 15:29 +0100, Benjamin Tissoires wrote:
> [...]
>
> > @@ -12021,6 +12034,12 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> > if (ret)
> > return ret;
> > break;
> > + case KF_ARG_PTR_TO_TIMER:
> > + if (reg->type != PTR_TO_MAP_VALUE) {
> > + verbose(env, "arg#%d doesn't point to a map value\n", i);
> > + return -EINVAL;
> > + }
> > + break;
>
> I think that pointer offset has to be checked as well,
> otherwise the following program verifies w/o error:
I initially thought it would be harder than it actually was.
Fixed (with the new test below) in v5.
Cheers,
Benjamin
>
> --- 8< ----------------------------
>
> #include <linux/bpf.h>
> #include <time.h>
> #include <errno.h>
> #include <bpf/bpf_helpers.h>
> #include "bpf_tcp_helpers.h"
>
> extern int bpf_timer_set_sleepable_cb_impl(struct bpf_timer *timer,
> int (callback_fn)(void *map, int *key, struct bpf_timer *timer), void *aux__ign) __ksym;
>
> #define bpf_timer_set_sleepable_cb(timer, cb) \
> bpf_timer_set_sleepable_cb_impl(timer, cb, NULL)
>
> struct elem {
> struct bpf_timer t;
> };
>
> struct {
> __uint(type, BPF_MAP_TYPE_ARRAY);
> __uint(max_entries, 2);
> __type(key, int);
> __type(value, struct elem);
> } array SEC(".maps");
>
> static int cb_sleepable(void *map, int *key, struct bpf_timer *timer)
> {
> return 0;
> }
>
> SEC("fentry/bpf_fentry_test5")
> int BPF_PROG2(test_sleepable, int, a)
> {
> struct bpf_timer *arr_timer;
> int array_key = 1;
>
> arr_timer = bpf_map_lookup_elem(&array, &array_key);
> if (!arr_timer)
> return 0;
> bpf_timer_init(arr_timer, &array, CLOCK_MONOTONIC);
> bpf_timer_set_sleepable_cb((void *)arr_timer + 1, // <-- note incorrect offset
> cb_sleepable);
> bpf_timer_start(arr_timer, 0, 0);
> return 0;
> }
>
> char _license[] SEC("license") = "GPL";
>
> ---------------------------- >8 ---
>
On Fri, 2024-03-15 at 15:29 +0100, Benjamin Tissoires wrote:
[...]
> @@ -12021,6 +12034,12 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> if (ret)
> return ret;
> break;
> + case KF_ARG_PTR_TO_TIMER:
> + if (reg->type != PTR_TO_MAP_VALUE) {
> + verbose(env, "arg#%d doesn't point to a map value\n", i);
> + return -EINVAL;
> + }
> + break;
I think that pointer offset has to be checked as well,
otherwise the following program verifies w/o error:
--- 8< ----------------------------
#include <linux/bpf.h>
#include <time.h>
#include <errno.h>
#include <bpf/bpf_helpers.h>
#include "bpf_tcp_helpers.h"
extern int bpf_timer_set_sleepable_cb_impl(struct bpf_timer *timer,
int (callback_fn)(void *map, int *key, struct bpf_timer *timer), void *aux__ign) __ksym;
#define bpf_timer_set_sleepable_cb(timer, cb) \
bpf_timer_set_sleepable_cb_impl(timer, cb, NULL)
struct elem {
struct bpf_timer t;
};
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 2);
__type(key, int);
__type(value, struct elem);
} array SEC(".maps");
static int cb_sleepable(void *map, int *key, struct bpf_timer *timer)
{
return 0;
}
SEC("fentry/bpf_fentry_test5")
int BPF_PROG2(test_sleepable, int, a)
{
struct bpf_timer *arr_timer;
int array_key = 1;
arr_timer = bpf_map_lookup_elem(&array, &array_key);
if (!arr_timer)
return 0;
bpf_timer_init(arr_timer, &array, CLOCK_MONOTONIC);
bpf_timer_set_sleepable_cb((void *)arr_timer + 1, // <-- note incorrect offset
cb_sleepable);
bpf_timer_start(arr_timer, 0, 0);
return 0;
}
char _license[] SEC("license") = "GPL";
---------------------------- >8 ---