From: Joanne Koong <joannekoong@fb.com>
Date: Mon, 29 Nov 2021 19:06:19 -0800
Subject: bpf: Add bpf_loop helper
Patch-mainline: v5.17-rc1
Git-commit: e6f2dd0f80674e9d5960337b3e9c2a242441b326
References: jsc#PED-1368
This patch adds the kernel-side and API changes for a new helper
function, bpf_loop:
long bpf_loop(u32 nr_loops, void *callback_fn, void *callback_ctx,
u64 flags);
where long (*callback_fn)(u32 index, void *ctx);
bpf_loop invokes the "callback_fn" **nr_loops** times or until the
callback_fn returns 1. The callback_fn can only return 0 or 1, and
this is enforced by the verifier. The callback_fn index is zero-indexed.
A few things to please note:
~ The "u64 flags" parameter is currently unused but is included in
case a future use case for it arises.
~ In the kernel-side implementation of bpf_loop (kernel/bpf/bpf_iter.c),
bpf_callback_t is used as the callback function cast.
~ A program can have nested bpf_loop calls but the program must
still adhere to the verifier constraint of its stack depth (the stack depth
cannot exceed MAX_BPF_STACK))
~ Recursive callback_fns do not pass the verifier, due to the call stack
for these being too deep.
~ The next patch will include the tests and benchmark
Signed-off-by: Joanne Koong <joannekoong@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211130030622.4131246-2-joannekoong@fb.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
include/linux/bpf.h | 1
include/uapi/linux/bpf.h | 25 +++++++++++
kernel/bpf/bpf_iter.c | 35 ++++++++++++++++
kernel/bpf/helpers.c | 2
kernel/bpf/verifier.c | 88 +++++++++++++++++++++++++----------------
tools/include/uapi/linux/bpf.h | 25 +++++++++++
6 files changed, 142 insertions(+), 34 deletions(-)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2155,6 +2155,7 @@ extern const struct bpf_func_proto bpf_s
extern const struct bpf_func_proto bpf_sk_getsockopt_proto;
extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
extern const struct bpf_func_proto bpf_find_vma_proto;
+extern const struct bpf_func_proto bpf_loop_proto;
const struct bpf_func_proto *tracing_prog_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4957,6 +4957,30 @@ union bpf_attr {
* **-ENOENT** if *task->mm* is NULL, or no vma contains *addr*.
* **-EBUSY** if failed to try lock mmap_lock.
* **-EINVAL** for invalid **flags**.
+ *
+ * long bpf_loop(u32 nr_loops, void *callback_fn, void *callback_ctx, u64 flags)
+ * Description
+ * For **nr_loops**, call **callback_fn** function
+ * with **callback_ctx** as the context parameter.
+ * The **callback_fn** should be a static function and
+ * the **callback_ctx** should be a pointer to the stack.
+ * The **flags** is used to control certain aspects of the helper.
+ * Currently, the **flags** must be 0. Currently, nr_loops is
+ * limited to 1 << 23 (~8 million) loops.
+ *
+ * long (\*callback_fn)(u32 index, void \*ctx);
+ *
+ * where **index** is the current index in the loop. The index
+ * is zero-indexed.
+ *
+ * If **callback_fn** returns 0, the helper will continue to the next
+ * loop. If return value is 1, the helper will skip the rest of
+ * the loops and return. Other return values are not used now,
+ * and will be rejected by the verifier.
+ *
+ * Return
+ * The number of loops performed, **-EINVAL** for invalid **flags**,
+ * **-E2BIG** if **nr_loops** exceeds the maximum number of loops.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5140,6 +5164,7 @@ union bpf_attr {
FN(skc_to_unix_sock), \
FN(kallsyms_lookup_name), \
FN(find_vma), \
+ FN(loop), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -714,3 +714,38 @@ const struct bpf_func_proto bpf_for_each
.arg3_type = ARG_PTR_TO_STACK_OR_NULL,
.arg4_type = ARG_ANYTHING,
};
+
+/* maximum number of loops */
+#define MAX_LOOPS BIT(23)
+
+BPF_CALL_4(bpf_loop, u32, nr_loops, void *, callback_fn, void *, callback_ctx,
+ u64, flags)
+{
+ bpf_callback_t callback = (bpf_callback_t)callback_fn;
+ u64 ret;
+ u32 i;
+
+ if (flags)
+ return -EINVAL;
+ if (nr_loops > MAX_LOOPS)
+ return -E2BIG;
+
+ for (i = 0; i < nr_loops; i++) {
+ ret = callback((u64)i, (u64)(long)callback_ctx, 0, 0, 0);
+ /* return value: 0 - continue, 1 - stop and return */
+ if (ret)
+ return i + 1;
+ }
+
+ return i;
+}
+
+const struct bpf_func_proto bpf_loop_proto = {
+ .func = bpf_loop,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_ANYTHING,
+ .arg2_type = ARG_PTR_TO_FUNC,
+ .arg3_type = ARG_PTR_TO_STACK_OR_NULL,
+ .arg4_type = ARG_ANYTHING,
+};
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1376,6 +1376,8 @@ bpf_base_func_proto(enum bpf_func_id fun
return &bpf_ringbuf_query_proto;
case BPF_FUNC_for_each_map_elem:
return &bpf_for_each_map_elem_proto;
+ case BPF_FUNC_loop:
+ return &bpf_loop_proto;
default:
break;
}
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6120,6 +6120,27 @@ static int set_map_elem_callback_state(s
return 0;
}
+static int set_loop_callback_state(struct bpf_verifier_env *env,
+ struct bpf_func_state *caller,
+ struct bpf_func_state *callee,
+ int insn_idx)
+{
+ /* bpf_loop(u32 nr_loops, void *callback_fn, void *callback_ctx,
+ * u64 flags);
+ * callback_fn(u32 index, void *callback_ctx);
+ */
+ callee->regs[BPF_REG_1].type = SCALAR_VALUE;
+ callee->regs[BPF_REG_2] = caller->regs[BPF_REG_3];
+
+ /* unused */
+ __mark_reg_not_init(env, &callee->regs[BPF_REG_3]);
+ __mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
+ __mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
+
+ callee->in_callback_fn = true;
+ return 0;
+}
+
static int set_timer_callback_state(struct bpf_verifier_env *env,
struct bpf_func_state *caller,
struct bpf_func_state *callee,
@@ -6493,13 +6514,7 @@ static int check_helper_call(struct bpf_
return err;
}
- if (func_id == BPF_FUNC_tail_call) {
- err = check_reference_leak(env);
- if (err) {
- verbose(env, "tail_call would lead to reference leak\n");
- return err;
- }
- } else if (is_release_function(func_id)) {
+ if (is_release_function(func_id)) {
err = release_reference(env, meta.ref_obj_id);
if (err) {
verbose(env, "func %s#%d reference has not been acquired before\n",
@@ -6510,42 +6525,47 @@ static int check_helper_call(struct bpf_
regs = cur_regs(env);
- /* check that flags argument in get_local_storage(map, flags) is 0,
- * this is required because get_local_storage() can't return an error.
- */
- if (func_id == BPF_FUNC_get_local_storage &&
- !register_is_null(®s[BPF_REG_2])) {
- verbose(env, "get_local_storage() doesn't support non-zero flags\n");
- return -EINVAL;
- }
-
- if (func_id == BPF_FUNC_for_each_map_elem) {
+ switch (func_id) {
+ case BPF_FUNC_tail_call:
+ err = check_reference_leak(env);
+ if (err) {
+ verbose(env, "tail_call would lead to reference leak\n");
+ return err;
+ }
+ break;
+ case BPF_FUNC_get_local_storage:
+ /* check that flags argument in get_local_storage(map, flags) is 0,
+ * this is required because get_local_storage() can't return an error.
+ */
+ if (!register_is_null(®s[BPF_REG_2])) {
+ verbose(env, "get_local_storage() doesn't support non-zero flags\n");
+ return -EINVAL;
+ }
+ break;
+ case BPF_FUNC_for_each_map_elem:
err = __check_func_call(env, insn, insn_idx_p, meta.subprogno,
set_map_elem_callback_state);
- if (err < 0)
- return -EINVAL;
- }
-
- if (func_id == BPF_FUNC_timer_set_callback) {
+ break;
+ case BPF_FUNC_timer_set_callback:
err = __check_func_call(env, insn, insn_idx_p, meta.subprogno,
set_timer_callback_state);
- if (err < 0)
- return -EINVAL;
- }
-
- if (func_id == BPF_FUNC_find_vma) {
+ break;
+ case BPF_FUNC_find_vma:
err = __check_func_call(env, insn, insn_idx_p, meta.subprogno,
set_find_vma_callback_state);
- if (err < 0)
- return -EINVAL;
- }
-
- if (func_id == BPF_FUNC_snprintf) {
+ break;
+ case BPF_FUNC_snprintf:
err = check_bpf_snprintf_call(env, regs);
- if (err < 0)
- return err;
+ break;
+ case BPF_FUNC_loop:
+ err = __check_func_call(env, insn, insn_idx_p, meta.subprogno,
+ set_loop_callback_state);
+ break;
}
+ if (err)
+ return err;
+
/* reset caller saved regs */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
mark_reg_not_init(env, regs, caller_saved[i]);
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4960,6 +4960,30 @@ union bpf_attr {
* **-ENOENT** if *task->mm* is NULL, or no vma contains *addr*.
* **-EBUSY** if failed to try lock mmap_lock.
* **-EINVAL** for invalid **flags**.
+ *
+ * long bpf_loop(u32 nr_loops, void *callback_fn, void *callback_ctx, u64 flags)
+ * Description
+ * For **nr_loops**, call **callback_fn** function
+ * with **callback_ctx** as the context parameter.
+ * The **callback_fn** should be a static function and
+ * the **callback_ctx** should be a pointer to the stack.
+ * The **flags** is used to control certain aspects of the helper.
+ * Currently, the **flags** must be 0. Currently, nr_loops is
+ * limited to 1 << 23 (~8 million) loops.
+ *
+ * long (\*callback_fn)(u32 index, void \*ctx);
+ *
+ * where **index** is the current index in the loop. The index
+ * is zero-indexed.
+ *
+ * If **callback_fn** returns 0, the helper will continue to the next
+ * loop. If return value is 1, the helper will skip the rest of
+ * the loops and return. Other return values are not used now,
+ * and will be rejected by the verifier.
+ *
+ * Return
+ * The number of loops performed, **-EINVAL** for invalid **flags**,
+ * **-E2BIG** if **nr_loops** exceeds the maximum number of loops.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5143,6 +5167,7 @@ union bpf_attr {
FN(skc_to_unix_sock), \
FN(kallsyms_lookup_name), \
FN(find_vma), \
+ FN(loop), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper