From 6018e1f407cccf39b804d1f75ad4de7be4e6cc45 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Wed, 8 Mar 2023 10:41:17 -0800 Subject: [PATCH] bpf: implement numbers iterator Implement the first open-coded iterator type over a range of integers. It's public API consists of: - bpf_iter_num_new() constructor, which accepts [start, end) range (that is, start is inclusive, end is exclusive). - bpf_iter_num_next() which will keep returning read-only pointer to int until the range is exhausted, at which point NULL will be returned. If bpf_iter_num_next() is kept calling after this, NULL will be persistently returned. - bpf_iter_num_destroy() destructor, which needs to be called at some point to clean up iterator state. BPF verifier enforces that iterator destructor is called at some point before BPF program exits. Note that `start = end = X` is a valid combination to setup an empty iterator. bpf_iter_num_new() will return 0 (success) for any such combination. If bpf_iter_num_new() detects invalid combination of input arguments, it returns error, resets iterator state to, effectively, empty iterator, so any subsequent call to bpf_iter_num_next() will keep returning NULL. BPF verifier has no knowledge that returned integers are in the [start, end) value range, as both `start` and `end` are not statically known and enforced: they are runtime values. While the implementation is pretty trivial, some care needs to be taken to avoid overflows and underflows. Subsequent selftests will validate correctness of [start, end) semantics, especially around extremes (INT_MIN and INT_MAX). Similarly to bpf_loop(), we enforce that no more than BPF_MAX_LOOPS can be specified. bpf_iter_num_{new,next,destroy}() is a logical evolution from bounded BPF loops and bpf_loop() helper and is the basis for implementing ergonomic BPF loops with no statically known or verified bounds. Subsequent patches implement bpf_for() macro, demonstrating how this can be wrapped into something that works and feels like a normal for() loop in C language. Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20230308184121.1165081-5-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 8 +++- include/uapi/linux/bpf.h | 8 ++++ kernel/bpf/bpf_iter.c | 70 ++++++++++++++++++++++++++++++++++ kernel/bpf/helpers.c | 3 ++ tools/include/uapi/linux/bpf.h | 8 ++++ 5 files changed, 95 insertions(+), 2 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 6792a7940e1e..e64ff1e89fb2 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1617,8 +1617,12 @@ struct bpf_array { #define BPF_COMPLEXITY_LIMIT_INSNS 1000000 /* yes. 1M insns */ #define MAX_TAIL_CALL_CNT 33 -/* Maximum number of loops for bpf_loop */ -#define BPF_MAX_LOOPS BIT(23) +/* Maximum number of loops for bpf_loop and bpf_iter_num. + * It's enum to expose it (and thus make it discoverable) through BTF. + */ +enum { + BPF_MAX_LOOPS = 8 * 1024 * 1024, +}; #define BPF_F_ACCESS_MASK (BPF_F_RDONLY | \ BPF_F_RDONLY_PROG | \ diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 976b194eb775..4abddb668a10 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -7112,4 +7112,12 @@ enum { BPF_F_TIMER_ABS = (1ULL << 0), }; +/* BPF numbers iterator state */ +struct bpf_iter_num { + /* opaque iterator state; having __u64 here allows to preserve correct + * alignment requirements in vmlinux.h, generated from BTF + */ + __u64 __opaque[1]; +} __attribute__((aligned(8))); + #endif /* _UAPI__LINUX_BPF_H__ */ diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c index 5dc307bdeaeb..96856f130cbf 100644 --- a/kernel/bpf/bpf_iter.c +++ b/kernel/bpf/bpf_iter.c @@ -776,3 +776,73 @@ const struct bpf_func_proto bpf_loop_proto = { .arg3_type = ARG_PTR_TO_STACK_OR_NULL, .arg4_type = ARG_ANYTHING, }; + +struct bpf_iter_num_kern { + int cur; /* current value, inclusive */ + int end; /* final value, exclusive */ +} __aligned(8); + +__diag_push(); +__diag_ignore_all("-Wmissing-prototypes", + "Global functions as their definitions will be in vmlinux BTF"); + +__bpf_kfunc int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end) +{ + struct bpf_iter_num_kern *s = (void *)it; + + BUILD_BUG_ON(sizeof(struct bpf_iter_num_kern) != sizeof(struct bpf_iter_num)); + BUILD_BUG_ON(__alignof__(struct bpf_iter_num_kern) != __alignof__(struct bpf_iter_num)); + + BTF_TYPE_EMIT(struct btf_iter_num); + + /* start == end is legit, it's an empty range and we'll just get NULL + * on first (and any subsequent) bpf_iter_num_next() call + */ + if (start > end) { + s->cur = s->end = 0; + return -EINVAL; + } + + /* avoid overflows, e.g., if start == INT_MIN and end == INT_MAX */ + if ((s64)end - (s64)start > BPF_MAX_LOOPS) { + s->cur = s->end = 0; + return -E2BIG; + } + + /* user will call bpf_iter_num_next() first, + * which will set s->cur to exactly start value; + * underflow shouldn't matter + */ + s->cur = start - 1; + s->end = end; + + return 0; +} + +__bpf_kfunc int *bpf_iter_num_next(struct bpf_iter_num* it) +{ + struct bpf_iter_num_kern *s = (void *)it; + + /* check failed initialization or if we are done (same behavior); + * need to be careful about overflow, so convert to s64 for checks, + * e.g., if s->cur == s->end == INT_MAX, we can't just do + * s->cur + 1 >= s->end + */ + if ((s64)(s->cur + 1) >= s->end) { + s->cur = s->end = 0; + return NULL; + } + + s->cur++; + + return &s->cur; +} + +__bpf_kfunc void bpf_iter_num_destroy(struct bpf_iter_num *it) +{ + struct bpf_iter_num_kern *s = (void *)it; + + s->cur = s->end = 0; +} + +__diag_pop(); diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 637ac4e92e75..f9b7eeedce08 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2411,6 +2411,9 @@ BTF_ID_FLAGS(func, bpf_rcu_read_lock) BTF_ID_FLAGS(func, bpf_rcu_read_unlock) BTF_ID_FLAGS(func, bpf_dynptr_slice, KF_RET_NULL) BTF_ID_FLAGS(func, bpf_dynptr_slice_rdwr, KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_iter_num_new, KF_ITER_NEW) +BTF_ID_FLAGS(func, bpf_iter_num_next, KF_ITER_NEXT | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY) BTF_SET8_END(common_btf_ids) static const struct btf_kfunc_id_set common_kfunc_set = { diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 976b194eb775..4abddb668a10 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -7112,4 +7112,12 @@ enum { BPF_F_TIMER_ABS = (1ULL << 0), }; +/* BPF numbers iterator state */ +struct bpf_iter_num { + /* opaque iterator state; having __u64 here allows to preserve correct + * alignment requirements in vmlinux.h, generated from BTF + */ + __u64 __opaque[1]; +} __attribute__((aligned(8))); + #endif /* _UAPI__LINUX_BPF_H__ */