On Tue, Dec 17, 2024 at 5:24 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Tue, Dec 17, 2024 at 4:58 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote: > > > > On 12/13/24 3:29 PM, Amery Hung wrote: > > > Allows struct_ops programs to acqurie referenced kptrs from arguments > > > by directly reading the argument. > > > > > > The verifier will acquire a reference for struct_ops a argument tagged > > > with "__ref" in the stub function in the beginning of the main program. > > > The user will be able to access the referenced kptr directly by reading > > > the context as long as it has not been released by the program. > > > > > > This new mechanism to acquire referenced kptr (compared to the existing > > > "kfunc with KF_ACQUIRE") is introduced for ergonomic and semantic reasons. > > > In the first use case, Qdisc_ops, an skb is passed to .enqueue in the > > > first argument. This mechanism provides a natural way for users to get a > > > referenced kptr in the .enqueue struct_ops programs and makes sure that a > > > qdisc will always enqueue or drop the skb. > > > > > > Signed-off-by: Amery Hung <amery.hung@xxxxxxxxxxxxx> > > > --- > > > include/linux/bpf.h | 3 +++ > > > kernel/bpf/bpf_struct_ops.c | 26 ++++++++++++++++++++------ > > > kernel/bpf/btf.c | 1 + > > > kernel/bpf/verifier.c | 35 ++++++++++++++++++++++++++++++++--- > > > 4 files changed, 56 insertions(+), 9 deletions(-) > > > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > > index 1b84613b10ac..72bf941d1daf 100644 > > > --- a/include/linux/bpf.h > > > +++ b/include/linux/bpf.h > > > @@ -968,6 +968,7 @@ struct bpf_insn_access_aux { > > > struct { > > > struct btf *btf; > > > u32 btf_id; > > > + u32 ref_obj_id; > > > }; > > > }; > > > struct bpf_verifier_log *log; /* for verbose logs */ > > > @@ -1480,6 +1481,8 @@ struct bpf_ctx_arg_aux { > > > enum bpf_reg_type reg_type; > > > struct btf *btf; > > > u32 btf_id; > > > + u32 ref_obj_id; > > > + bool refcounted; > > > }; > > > > > > struct btf_mod_pair { > > > diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c > > > index fda3dd2ee984..6e7795744f6a 100644 > > > --- a/kernel/bpf/bpf_struct_ops.c > > > +++ b/kernel/bpf/bpf_struct_ops.c > > > @@ -145,6 +145,7 @@ void bpf_struct_ops_image_free(void *image) > > > } > > > > > > #define MAYBE_NULL_SUFFIX "__nullable" > > > +#define REFCOUNTED_SUFFIX "__ref" > > > #define MAX_STUB_NAME 128 > > > > > > /* Return the type info of a stub function, if it exists. > > > @@ -206,9 +207,11 @@ static int prepare_arg_info(struct btf *btf, > > > struct bpf_struct_ops_arg_info *arg_info) > > > { > > > const struct btf_type *stub_func_proto, *pointed_type; > > > + bool is_nullable = false, is_refcounted = false; > > > const struct btf_param *stub_args, *args; > > > struct bpf_ctx_arg_aux *info, *info_buf; > > > u32 nargs, arg_no, info_cnt = 0; > > > + const char *suffix; > > > u32 arg_btf_id; > > > int offset; > > > > > > @@ -240,12 +243,19 @@ static int prepare_arg_info(struct btf *btf, > > > info = info_buf; > > > for (arg_no = 0; arg_no < nargs; arg_no++) { > > > /* Skip arguments that is not suffixed with > > > - * "__nullable". > > > + * "__nullable or __ref". > > > */ > > > - if (!btf_param_match_suffix(btf, &stub_args[arg_no], > > > - MAYBE_NULL_SUFFIX)) > > > + is_nullable = btf_param_match_suffix(btf, &stub_args[arg_no], > > > + MAYBE_NULL_SUFFIX); > > > + is_refcounted = btf_param_match_suffix(btf, &stub_args[arg_no], > > > + REFCOUNTED_SUFFIX); > > > + if (!is_nullable && !is_refcounted) > > > continue; > > > > > > + if (is_nullable) > > > + suffix = MAYBE_NULL_SUFFIX; > > > + else if (is_refcounted) > > > + suffix = REFCOUNTED_SUFFIX; > > > /* Should be a pointer to struct */ > > > pointed_type = btf_type_resolve_ptr(btf, > > > args[arg_no].type, > > > @@ -253,7 +263,7 @@ static int prepare_arg_info(struct btf *btf, > > > if (!pointed_type || > > > !btf_type_is_struct(pointed_type)) { > > > pr_warn("stub function %s__%s has %s tagging to an unsupported type\n", > > > - st_ops_name, member_name, MAYBE_NULL_SUFFIX); > > > + st_ops_name, member_name, suffix); > > > goto err_out; > > > } > > > > > > @@ -271,11 +281,15 @@ static int prepare_arg_info(struct btf *btf, > > > } > > > > > > /* Fill the information of the new argument */ > > > - info->reg_type = > > > - PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL; > > > info->btf_id = arg_btf_id; > > > info->btf = btf; > > > info->offset = offset; > > > + if (is_nullable) { > > > + info->reg_type = PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL; > > > + } else if (is_refcounted) { > > > + info->reg_type = PTR_TRUSTED | PTR_TO_BTF_ID; > > > + info->refcounted = true; > > > + } > > > > > > info++; > > > info_cnt++; > > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > > > index e7a59e6462a9..a05ccf9ee032 100644 > > > --- a/kernel/bpf/btf.c > > > +++ b/kernel/bpf/btf.c > > > @@ -6580,6 +6580,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, > > > info->reg_type = ctx_arg_info->reg_type; > > > info->btf = ctx_arg_info->btf ? : btf_vmlinux; > > > info->btf_id = ctx_arg_info->btf_id; > > > + info->ref_obj_id = ctx_arg_info->ref_obj_id; > > > return true; > > > } > > > } > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > > index 9f5de8d4fbd0..69753096075f 100644 > > > --- a/kernel/bpf/verifier.c > > > +++ b/kernel/bpf/verifier.c > > > @@ -1402,6 +1402,17 @@ static int release_reference_state(struct bpf_func_state *state, int ptr_id) > > > return -EINVAL; > > > } > > > > > > +static bool find_reference_state(struct bpf_func_state *state, int ptr_id) > > > +{ > > > + int i; > > > + > > > + for (i = 0; i < state->acquired_refs; i++) > > > + if (state->refs[i].id == ptr_id) > > > + return true; > > > + > > > + return false; > > > +} > > > + > > > static int release_lock_state(struct bpf_func_state *state, int type, int id, void *ptr) > > > { > > > int i, last_idx; > > > @@ -5798,7 +5809,8 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off, > > > /* check access to 'struct bpf_context' fields. Supports fixed offsets only */ > > > static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, int size, > > > enum bpf_access_type t, enum bpf_reg_type *reg_type, > > > - struct btf **btf, u32 *btf_id, bool *is_retval, bool is_ldsx) > > > + struct btf **btf, u32 *btf_id, bool *is_retval, bool is_ldsx, > > > + u32 *ref_obj_id) > > > { > > > struct bpf_insn_access_aux info = { > > > .reg_type = *reg_type, > > > @@ -5820,8 +5832,16 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, > > > *is_retval = info.is_retval; > > > > > > if (base_type(*reg_type) == PTR_TO_BTF_ID) { > > > + if (info.ref_obj_id && > > > + !find_reference_state(cur_func(env), info.ref_obj_id)) { > > > + verbose(env, "invalid bpf_context access off=%d. Reference may already be released\n", > > > + off); > > > + return -EACCES; > > > + } > > > + > > > *btf = info.btf; > > > *btf_id = info.btf_id; > > > + *ref_obj_id = info.ref_obj_id; > > > } else { > > > env->insn_aux_data[insn_idx].ctx_field_size = info.ctx_field_size; > > > } > > > @@ -7135,7 +7155,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn > > > struct bpf_retval_range range; > > > enum bpf_reg_type reg_type = SCALAR_VALUE; > > > struct btf *btf = NULL; > > > - u32 btf_id = 0; > > > + u32 btf_id = 0, ref_obj_id = 0; > > > > > > if (t == BPF_WRITE && value_regno >= 0 && > > > is_pointer_value(env, value_regno)) { > > > @@ -7148,7 +7168,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn > > > return err; > > > > > > err = check_ctx_access(env, insn_idx, off, size, t, ®_type, &btf, > > > - &btf_id, &is_retval, is_ldsx); > > > + &btf_id, &is_retval, is_ldsx, &ref_obj_id); > > > if (err) > > > verbose_linfo(env, insn_idx, "; "); > > > if (!err && t == BPF_READ && value_regno >= 0) { > > > @@ -7179,6 +7199,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn > > > if (base_type(reg_type) == PTR_TO_BTF_ID) { > > > regs[value_regno].btf = btf; > > > regs[value_regno].btf_id = btf_id; > > > + regs[value_regno].ref_obj_id = ref_obj_id; > > > } > > > } > > > regs[value_regno].type = reg_type; > > > @@ -21662,6 +21683,7 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog) > > > { > > > bool pop_log = !(env->log.level & BPF_LOG_LEVEL2); > > > struct bpf_subprog_info *sub = subprog_info(env, subprog); > > > + struct bpf_ctx_arg_aux *ctx_arg_info; > > > struct bpf_verifier_state *state; > > > struct bpf_reg_state *regs; > > > int ret, i; > > > @@ -21769,6 +21791,13 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog) > > > mark_reg_known_zero(env, regs, BPF_REG_1); > > > } > > > > > > + if (!subprog && env->prog->type == BPF_PROG_TYPE_STRUCT_OPS) { > > > + ctx_arg_info = (struct bpf_ctx_arg_aux *)env->prog->aux->ctx_arg_info; > > > + for (i = 0; i < env->prog->aux->ctx_arg_info_size; i++) > > > + if (ctx_arg_info[i].refcounted) > > > + ctx_arg_info[i].ref_obj_id = acquire_reference_state(env, 0); > > > > There is a conflict in the bpf-next/master. acquire_reference_state has been > > refactored in commit 769b0f1c8214. From looking at the net/sched/sch_*.c > > changes, they should not have conflict with the net-next/main. I would suggest > > to rebase this set on bpf-next/master. > > > > At the first glance, the ref_obj_id assignment looks racy because ctx_arg_info > > is shared by different bpf progs that may be verified in parallel. After another > > thought, this should be fine because it should always end up having the same > > ref_obj_id for the same arg-no, right? Not sure if UBSAN can understand this > > without using the READ/WRITE_ONCE. but adding READ/WRITE_ONCE when using > > ref_obj_id will be quite puzzling when reading the verifier code. Any better idea? > > ctx_arg_info is kinda read-only from the verifier pov. > bpf_ctx_arg_aux->btf_id is populated before the main verifier loop. > While ref_obj_id is a dynamic property. > It doesn't really fit in bpf_ctx_arg_aux. > It probably needs to be another struct type that is allocated > and populated once with acquire_reference() when the main verifier loop > is happening. > do_check_common() maybe too early? > Looks like it's anyway a reference that is ok to leak per patch 3 ? > > It seems the main goal is to pass ref_obj_id-like argument into bpf prog > and make sure that prog doesn't call KF_RELEASE kfunc on it twice, > but leaking is ok? > Maybe it needs a different type. Other than REF_TYPE_PTR. > The main goal of this patch is to get a unique ref_obj_id to the skb arg in a .enqueue call. Therefore, we acquire that one and only ref_obj_id for __ref arg early in do_check_common() and do not change it afterward. Later in the main loop, the liviness is tracked in the reference states. This feels kind of read-only? Besides, since we acquire the ref automatically, it forces the user to do something with the ref ptr (in qdisc's case, .enqueue needs to either drop or enqueue it). I try to break down the requirements from bpf qdisc (1. only a unique reference to the skb in .enqueue; 2. users must enqueue or drop the skb in .enqueue; 3. dequeue a single skb) into two orthogonal patches 1 and 3. so whether this reference can leak or not can be independent. Taking a step back, maybe we can encapsulate them all in one semantic (a new kind of REF like you suggest), but I am not sure if that'd be too specific and then less useful to others. > > Other than the subprog, afaik, the bpf prog triggered by the bpf_tail_call can > > also take the 'u64 *ctx' array. May be disallow using tailcall in all ops in the > > bpf qdisc. env->subprog_info[i].has_tail_call has already tracked whether the > > tail_call is used. > > +1. Just disallow tail_call. Got it. Also, thanks Martin for pointing it out.