From: Kumar Kartikeya Dwivedi memxor@gmail.com
[ Upstream commit 8f14852e89113d738c99c375b4c8b8b7e1073df1 ]
Add a new type flag for bpf_arg_type that when set tells verifier that for a release function, that argument's register will be the one for which meta.ref_obj_id will be set, and which will then be released using release_reference. To capture the regno, introduce a new field release_regno in bpf_call_arg_meta.
This would be required in the next patch, where we may either pass NULL or a refcounted pointer as an argument to the release function bpf_kptr_xchg. Just releasing only when meta.ref_obj_id is set is not enough, as there is a case where the type of argument needed matches, but the ref_obj_id is set to 0. Hence, we must enforce that whenever meta.ref_obj_id is zero, the register that is to be released can only be NULL for a release function.
Since we now indicate whether an argument is to be released in bpf_func_proto itself, is_release_function helper has lost its utitlity, hence refactor code to work without it, and just rely on meta.release_regno to know when to release state for a ref_obj_id. Still, the restriction of one release argument and only one ref_obj_id passed to BPF helper or kfunc remains. This may be lifted in the future.
Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20220424214901.2743946-3-memxor@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/bpf.h | 5 +- include/linux/bpf_verifier.h | 3 +- kernel/bpf/btf.c | 11 ++- kernel/bpf/ringbuf.c | 4 +- kernel/bpf/verifier.c | 76 +++++++++++-------- net/core/filter.c | 2 +- .../selftests/bpf/verifier/ref_tracking.c | 2 +- tools/testing/selftests/bpf/verifier/sock.c | 6 +- 8 files changed, 60 insertions(+), 49 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 00d55c10d876..2feae4a24d99 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -366,7 +366,10 @@ enum bpf_type_flag { */ MEM_PERCPU = BIT(4 + BPF_BASE_TYPE_BITS),
- __BPF_TYPE_LAST_FLAG = MEM_PERCPU, + /* Indicates that the argument will be released. */ + OBJ_RELEASE = BIT(5 + BPF_BASE_TYPE_BITS), + + __BPF_TYPE_LAST_FLAG = OBJ_RELEASE, };
/* Max number of base types. */ diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 3a9d2d7cc6b7..1f1e7f2ea967 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -523,8 +523,7 @@ int check_ptr_off_reg(struct bpf_verifier_env *env, const struct bpf_reg_state *reg, int regno); int check_func_arg_reg_off(struct bpf_verifier_env *env, const struct bpf_reg_state *reg, int regno, - enum bpf_arg_type arg_type, - bool is_release_func); + enum bpf_arg_type arg_type); int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg, u32 regno); int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg, diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index cbb48eb8c009..752de8112206 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5994,6 +5994,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, * verifier sees. */ for (i = 0; i < nargs; i++) { + enum bpf_arg_type arg_type = ARG_DONTCARE; u32 regno = i + 1; struct bpf_reg_state *reg = ®s[regno];
@@ -6014,7 +6015,9 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id); ref_tname = btf_name_by_offset(btf, ref_t->name_off);
- ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE, rel); + if (rel && reg->ref_obj_id) + arg_type |= OBJ_RELEASE; + ret = check_func_arg_reg_off(env, reg, regno, arg_type); if (ret < 0) return ret;
@@ -6045,11 +6048,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, if (reg->type == PTR_TO_BTF_ID) { reg_btf = reg->btf; reg_ref_id = reg->btf_id; - /* Ensure only one argument is referenced - * PTR_TO_BTF_ID, check_func_arg_reg_off relies - * on only one referenced register being allowed - * for kfuncs. - */ + /* Ensure only one argument is referenced PTR_TO_BTF_ID */ if (reg->ref_obj_id) { if (ref_obj_id) { bpf_log(log, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n", diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c index 710ba9de12ce..5173fd37590f 100644 --- a/kernel/bpf/ringbuf.c +++ b/kernel/bpf/ringbuf.c @@ -404,7 +404,7 @@ BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags) const struct bpf_func_proto bpf_ringbuf_submit_proto = { .func = bpf_ringbuf_submit, .ret_type = RET_VOID, - .arg1_type = ARG_PTR_TO_ALLOC_MEM, + .arg1_type = ARG_PTR_TO_ALLOC_MEM | OBJ_RELEASE, .arg2_type = ARG_ANYTHING, };
@@ -417,7 +417,7 @@ BPF_CALL_2(bpf_ringbuf_discard, void *, sample, u64, flags) const struct bpf_func_proto bpf_ringbuf_discard_proto = { .func = bpf_ringbuf_discard, .ret_type = RET_VOID, - .arg1_type = ARG_PTR_TO_ALLOC_MEM, + .arg1_type = ARG_PTR_TO_ALLOC_MEM | OBJ_RELEASE, .arg2_type = ARG_ANYTHING, };
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b8d1060153c8..4f19a86c2682 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -245,6 +245,7 @@ struct bpf_call_arg_meta { struct bpf_map *map_ptr; bool raw_mode; bool pkt_access; + u8 release_regno; int regno; int access_size; int mem_size; @@ -471,17 +472,6 @@ static bool type_may_be_null(u32 type) return type & PTR_MAYBE_NULL; }
-/* Determine whether the function releases some resources allocated by another - * function call. The first reference type argument will be assumed to be - * released by release_reference(). - */ -static bool is_release_function(enum bpf_func_id func_id) -{ - return func_id == BPF_FUNC_sk_release || - func_id == BPF_FUNC_ringbuf_submit || - func_id == BPF_FUNC_ringbuf_discard; -} - static bool may_be_acquire_function(enum bpf_func_id func_id) { return func_id == BPF_FUNC_sk_lookup_tcp || @@ -5325,6 +5315,11 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) type == ARG_PTR_TO_LONG; }
+static bool arg_type_is_release(enum bpf_arg_type type) +{ + return type & OBJ_RELEASE; +} + static int int_ptr_type_to_size(enum bpf_arg_type type) { if (type == ARG_PTR_TO_INT) @@ -5535,11 +5530,10 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
int check_func_arg_reg_off(struct bpf_verifier_env *env, const struct bpf_reg_state *reg, int regno, - enum bpf_arg_type arg_type, - bool is_release_func) + enum bpf_arg_type arg_type) { - bool fixed_off_ok = false, release_reg; enum bpf_reg_type type = reg->type; + bool fixed_off_ok = false;
switch ((u32)type) { case SCALAR_VALUE: @@ -5557,7 +5551,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env, /* Some of the argument types nevertheless require a * zero register offset. */ - if (arg_type != ARG_PTR_TO_ALLOC_MEM) + if (base_type(arg_type) != ARG_PTR_TO_ALLOC_MEM) return 0; break; /* All the rest must be rejected, except PTR_TO_BTF_ID which allows @@ -5565,19 +5559,17 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env, */ case PTR_TO_BTF_ID: /* When referenced PTR_TO_BTF_ID is passed to release function, - * it's fixed offset must be 0. We rely on the property that - * only one referenced register can be passed to BPF helpers and - * kfuncs. In the other cases, fixed offset can be non-zero. + * it's fixed offset must be 0. In the other cases, fixed offset + * can be non-zero. */ - release_reg = is_release_func && reg->ref_obj_id; - if (release_reg && reg->off) { + if (arg_type_is_release(arg_type) && reg->off) { verbose(env, "R%d must have zero offset when passed to release func\n", regno); return -EINVAL; } - /* For release_reg == true, fixed_off_ok must be false, but we - * already checked and rejected reg->off != 0 above, so set to - * true to allow fixed offset for all other cases. + /* For arg is release pointer, fixed_off_ok must be false, but + * we already checked and rejected reg->off != 0 above, so set + * to true to allow fixed offset for all other cases. */ fixed_off_ok = true; break; @@ -5636,14 +5628,24 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, if (err) return err;
- err = check_func_arg_reg_off(env, reg, regno, arg_type, is_release_function(meta->func_id)); + err = check_func_arg_reg_off(env, reg, regno, arg_type); if (err) return err;
skip_type_check: - /* check_func_arg_reg_off relies on only one referenced register being - * allowed for BPF helpers. - */ + if (arg_type_is_release(arg_type)) { + if (!reg->ref_obj_id && !register_is_null(reg)) { + verbose(env, "R%d must be referenced when passed to release function\n", + regno); + return -EINVAL; + } + if (meta->release_regno) { + verbose(env, "verifier internal error: more than one release argument\n"); + return -EFAULT; + } + meta->release_regno = regno; + } + if (reg->ref_obj_id) { if (meta->ref_obj_id) { verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n", @@ -6151,7 +6153,8 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn) return true; }
-static int check_func_proto(const struct bpf_func_proto *fn, int func_id) +static int check_func_proto(const struct bpf_func_proto *fn, int func_id, + struct bpf_call_arg_meta *meta) { return check_raw_mode_ok(fn) && check_arg_pair_ok(fn) && @@ -6833,7 +6836,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn memset(&meta, 0, sizeof(meta)); meta.pkt_access = fn->pkt_access;
- err = check_func_proto(fn, func_id); + err = check_func_proto(fn, func_id, &meta); if (err) { verbose(env, "kernel subsystem misconfigured func %s#%d\n", func_id_name(func_id), func_id); @@ -6866,8 +6869,17 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn return err; }
- if (is_release_function(func_id)) { - err = release_reference(env, meta.ref_obj_id); + regs = cur_regs(env); + + if (meta.release_regno) { + err = -EINVAL; + if (meta.ref_obj_id) + err = release_reference(env, meta.ref_obj_id); + /* meta.ref_obj_id can only be 0 if register that is meant to be + * released is NULL, which must be > R0. + */ + else if (register_is_null(®s[meta.release_regno])) + err = 0; if (err) { verbose(env, "func %s#%d reference has not been acquired before\n", func_id_name(func_id), func_id); @@ -6875,8 +6887,6 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn } }
- regs = cur_regs(env); - switch (func_id) { case BPF_FUNC_tail_call: err = check_reference_leak(env); diff --git a/net/core/filter.c b/net/core/filter.c index d0b0c163d3f3..5db4fae23925 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6642,7 +6642,7 @@ static const struct bpf_func_proto bpf_sk_release_proto = { .func = bpf_sk_release, .gpl_only = false, .ret_type = RET_INTEGER, - .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON, + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON | OBJ_RELEASE, };
BPF_CALL_5(bpf_xdp_sk_lookup_udp, struct xdp_buff *, ctx, diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c index fbd682520e47..57a83d763ec1 100644 --- a/tools/testing/selftests/bpf/verifier/ref_tracking.c +++ b/tools/testing/selftests/bpf/verifier/ref_tracking.c @@ -796,7 +796,7 @@ }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .result = REJECT, - .errstr = "reference has not been acquired before", + .errstr = "R1 must be referenced when passed to release function", }, { /* !bpf_sk_fullsock(sk) is checked but !bpf_tcp_sock(sk) is not checked */ diff --git a/tools/testing/selftests/bpf/verifier/sock.c b/tools/testing/selftests/bpf/verifier/sock.c index 86b24cad27a7..d11d0b28be41 100644 --- a/tools/testing/selftests/bpf/verifier/sock.c +++ b/tools/testing/selftests/bpf/verifier/sock.c @@ -417,7 +417,7 @@ }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .result = REJECT, - .errstr = "reference has not been acquired before", + .errstr = "R1 must be referenced when passed to release function", }, { "bpf_sk_release(bpf_sk_fullsock(skb->sk))", @@ -436,7 +436,7 @@ }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .result = REJECT, - .errstr = "reference has not been acquired before", + .errstr = "R1 must be referenced when passed to release function", }, { "bpf_sk_release(bpf_tcp_sock(skb->sk))", @@ -455,7 +455,7 @@ }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .result = REJECT, - .errstr = "reference has not been acquired before", + .errstr = "R1 must be referenced when passed to release function", }, { "sk_storage_get(map, skb->sk, NULL, 0): value == NULL",