bpf: Remove hard-coded btf_vmlinux assumption from BPF verifier

Remove a permeating assumption thoughout BPF verifier of vmlinux BTF. Instead,
wherever BTF type IDs are involved, also track the instance of struct btf that
goes along with the type ID. This allows to gradually add support for kernel
module BTFs and using/tracking module types across BPF helper calls and
registers.

This patch also renames btf_id() function to btf_obj_id() to minimize naming
clash with using btf_id to denote BTF *type* ID, rather than BTF *object*'s ID.

Also, altough btf_vmlinux can't get destructed and thus doesn't need
refcounting, module BTFs need that, so apply BTF refcounting universally when
BPF program is using BTF-powered attachment (tp_btf, fentry/fexit, etc). This
makes for simpler clean up code.

Now that BTF type ID is not enough to uniquely identify a BTF type, extend BPF
trampoline key to include BTF object ID. To differentiate that from target
program BPF ID, set 31st bit of type ID. BTF type IDs (at least currently) are
not allowed to take full 32 bits, so there is no danger of confusing that bit
with a valid BTF type ID.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201203204634.1325171-10-andrii@kernel.org

1 files changed, 47 insertions, 30 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e333ce43f281..2f3950839b85 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -238,7 +238,9 @@ struct bpf_call_arg_meta {
 	u64 msize_max_value;
 	int ref_obj_id;
 	int func_id;
+	struct btf *btf;
 	u32 btf_id;
+	struct btf *ret_btf;
 	u32 ret_btf_id;
 };
 
@@ -556,10 +558,9 @@ static struct bpf_func_state *func(struct bpf_verifier_env *env,
 	return cur->frame[reg->frameno];
 }
 
-const char *kernel_type_name(u32 id)
+static const char *kernel_type_name(const struct btf* btf, u32 id)
 {
-	return btf_name_by_offset(btf_vmlinux,
-				  btf_type_by_id(btf_vmlinux, id)->name_off);
+	return btf_name_by_offset(btf, btf_type_by_id(btf, id)->name_off);
 }
 
 static void print_verifier_state(struct bpf_verifier_env *env,
@@ -589,7 +590,7 @@ static void print_verifier_state(struct bpf_verifier_env *env,
 			if (t == PTR_TO_BTF_ID ||
 			    t == PTR_TO_BTF_ID_OR_NULL ||
 			    t == PTR_TO_PERCPU_BTF_ID)
-				verbose(env, "%s", kernel_type_name(reg->btf_id));
+				verbose(env, "%s", kernel_type_name(reg->btf, reg->btf_id));
 			verbose(env, "(id=%d", reg->id);
 			if (reg_type_may_be_refcounted_or_null(t))
 				verbose(env, ",ref_obj_id=%d", reg->ref_obj_id);
@@ -1383,7 +1384,8 @@ static void mark_reg_not_init(struct bpf_verifier_env *env,
 
 static void mark_btf_ld_reg(struct bpf_verifier_env *env,
 			    struct bpf_reg_state *regs, u32 regno,
-			    enum bpf_reg_type reg_type, u32 btf_id)
+			    enum bpf_reg_type reg_type,
+			    struct btf *btf, u32 btf_id)
 {
 	if (reg_type == SCALAR_VALUE) {
 		mark_reg_unknown(env, regs, regno);
@@ -1391,6 +1393,7 @@ static void mark_btf_ld_reg(struct bpf_verifier_env *env,
 	}
 	mark_reg_known_zero(env, regs, regno);
 	regs[regno].type = PTR_TO_BTF_ID;
+	regs[regno].btf = btf;
 	regs[regno].btf_id = btf_id;
 }
 
@@ -2764,7 +2767,7 @@ 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,
-			    u32 *btf_id)
+			    struct btf **btf, u32 *btf_id)
 {
 	struct bpf_insn_access_aux info = {
 		.reg_type = *reg_type,
@@ -2782,10 +2785,12 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off,
 		 */
 		*reg_type = info.reg_type;
 
-		if (*reg_type == PTR_TO_BTF_ID || *reg_type == PTR_TO_BTF_ID_OR_NULL)
+		if (*reg_type == PTR_TO_BTF_ID || *reg_type == PTR_TO_BTF_ID_OR_NULL) {
+			*btf = info.btf;
 			*btf_id = info.btf_id;
-		else
+		} else {
 			env->insn_aux_data[insn_idx].ctx_field_size = info.ctx_field_size;
+		}
 		/* remember the offset of last byte accessed in ctx */
 		if (env->prog->aux->max_ctx_offset < off + size)
 			env->prog->aux->max_ctx_offset = off + size;
@@ -3297,8 +3302,8 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 				   int value_regno)
 {
 	struct bpf_reg_state *reg = regs + regno;
-	const struct btf_type *t = btf_type_by_id(btf_vmlinux, reg->btf_id);
-	const char *tname = btf_name_by_offset(btf_vmlinux, t->name_off);
+	const struct btf_type *t = btf_type_by_id(reg->btf, reg->btf_id);
+	const char *tname = btf_name_by_offset(reg->btf, t->name_off);
 	u32 btf_id;
 	int ret;
 
@@ -3319,23 +3324,23 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 	}
 
 	if (env->ops->btf_struct_access) {
-		ret = env->ops->btf_struct_access(&env->log, t, off, size,
-						  atype, &btf_id);
+		ret = env->ops->btf_struct_access(&env->log, reg->btf, t,
+						  off, size, atype, &btf_id);
 	} else {
 		if (atype != BPF_READ) {
 			verbose(env, "only read is supported\n");
 			return -EACCES;
 		}
 
-		ret = btf_struct_access(&env->log, t, off, size, atype,
-					&btf_id);
+		ret = btf_struct_access(&env->log, reg->btf, t, off, size,
+					atype, &btf_id);
 	}
 
 	if (ret < 0)
 		return ret;
 
 	if (atype == BPF_READ && value_regno >= 0)
-		mark_btf_ld_reg(env, regs, value_regno, ret, btf_id);
+		mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id);
 
 	return 0;
 }
@@ -3385,12 +3390,12 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env,
 		return -EACCES;
 	}
 
-	ret = btf_struct_access(&env->log, t, off, size, atype, &btf_id);
+	ret = btf_struct_access(&env->log, btf_vmlinux, t, off, size, atype, &btf_id);
 	if (ret < 0)
 		return ret;
 
 	if (value_regno >= 0)
-		mark_btf_ld_reg(env, regs, value_regno, ret, btf_id);
+		mark_btf_ld_reg(env, regs, value_regno, ret, btf_vmlinux, btf_id);
 
 	return 0;
 }
@@ -3466,6 +3471,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 			mark_reg_unknown(env, regs, value_regno);
 	} else if (reg->type == PTR_TO_CTX) {
 		enum bpf_reg_type reg_type = SCALAR_VALUE;
+		struct btf *btf = NULL;
 		u32 btf_id = 0;
 
 		if (t == BPF_WRITE && value_regno >= 0 &&
@@ -3478,7 +3484,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 		if (err < 0)
 			return err;
 
-		err = check_ctx_access(env, insn_idx, off, size, t, &reg_type, &btf_id);
+		err = check_ctx_access(env, insn_idx, off, size, t, &reg_type, &btf, &btf_id);
 		if (err)
 			verbose_linfo(env, insn_idx, "; ");
 		if (!err && t == BPF_READ && value_regno >= 0) {
@@ -3500,8 +3506,10 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 				 */
 				regs[value_regno].subreg_def = DEF_NOT_SUBREG;
 				if (reg_type == PTR_TO_BTF_ID ||
-				    reg_type == PTR_TO_BTF_ID_OR_NULL)
+				    reg_type == PTR_TO_BTF_ID_OR_NULL) {
+					regs[value_regno].btf = btf;
 					regs[value_regno].btf_id = btf_id;
+				}
 			}
 			regs[value_regno].type = reg_type;
 		}
@@ -4118,11 +4126,11 @@ found:
 			arg_btf_id = compatible->btf_id;
 		}
 
-		if (!btf_struct_ids_match(&env->log, reg->off, reg->btf_id,
-					  *arg_btf_id)) {
+		if (!btf_struct_ids_match(&env->log, reg->btf, reg->btf_id, reg->off,
+					  btf_vmlinux, *arg_btf_id)) {
 			verbose(env, "R%d is of type %s but %s is expected\n",
-				regno, kernel_type_name(reg->btf_id),
-				kernel_type_name(*arg_btf_id));
+				regno, kernel_type_name(reg->btf, reg->btf_id),
+				kernel_type_name(btf_vmlinux, *arg_btf_id));
 			return -EACCES;
 		}
 
@@ -4244,6 +4252,7 @@ skip_type_check:
 			verbose(env, "Helper has invalid btf_id in R%d\n", regno);
 			return -EACCES;
 		}
+		meta->ret_btf = reg->btf;
 		meta->ret_btf_id = reg->btf_id;
 	} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
 		if (meta->func_id == BPF_FUNC_spin_lock) {
@@ -5190,16 +5199,16 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 		const struct btf_type *t;
 
 		mark_reg_known_zero(env, regs, BPF_REG_0);
-		t = btf_type_skip_modifiers(btf_vmlinux, meta.ret_btf_id, NULL);
+		t = btf_type_skip_modifiers(meta.ret_btf, meta.ret_btf_id, NULL);
 		if (!btf_type_is_struct(t)) {
 			u32 tsize;
 			const struct btf_type *ret;
 			const char *tname;
 
 			/* resolve the type size of ksym. */
-			ret = btf_resolve_size(btf_vmlinux, t, &tsize);
+			ret = btf_resolve_size(meta.ret_btf, t, &tsize);
 			if (IS_ERR(ret)) {
-				tname = btf_name_by_offset(btf_vmlinux, t->name_off);
+				tname = btf_name_by_offset(meta.ret_btf, t->name_off);
 				verbose(env, "unable to resolve the size of type '%s': %ld\n",
 					tname, PTR_ERR(ret));
 				return -EINVAL;
@@ -5212,6 +5221,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 			regs[BPF_REG_0].type =
 				fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID ?
 				PTR_TO_BTF_ID : PTR_TO_BTF_ID_OR_NULL;
+			regs[BPF_REG_0].btf = meta.ret_btf;
 			regs[BPF_REG_0].btf_id = meta.ret_btf_id;
 		}
 	} else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL ||
@@ -5228,6 +5238,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 				fn->ret_type, func_id_name(func_id), func_id);
 			return -EINVAL;
 		}
+		/* current BPF helper definitions are only coming from
+		 * built-in code with type IDs from  vmlinux BTF
+		 */
+		regs[BPF_REG_0].btf = btf_vmlinux;
 		regs[BPF_REG_0].btf_id = ret_btf_id;
 	} else {
 		verbose(env, "unknown return type %d of func %s#%d\n",
@@ -5627,7 +5641,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 		if (reg_is_pkt_pointer(ptr_reg)) {
 			dst_reg->id = ++env->id_gen;
 			/* something was added to pkt_ptr, set range to zero */
-			dst_reg->raw = 0;
+			memset(&dst_reg->raw, 0, sizeof(dst_reg->raw));
 		}
 		break;
 	case BPF_SUB:
@@ -5692,7 +5706,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 			dst_reg->id = ++env->id_gen;
 			/* something was added to pkt_ptr, set range to zero */
 			if (smin_val < 0)
-				dst_reg->raw = 0;
+				memset(&dst_reg->raw, 0, sizeof(dst_reg->raw));
 		}
 		break;
 	case BPF_AND:
@@ -7744,6 +7758,7 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			break;
 		case PTR_TO_BTF_ID:
 		case PTR_TO_PERCPU_BTF_ID:
+			dst_reg->btf = aux->btf_var.btf;
 			dst_reg->btf_id = aux->btf_var.btf_id;
 			break;
 		default:
@@ -9739,6 +9754,7 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
 	t = btf_type_skip_modifiers(btf_vmlinux, type, NULL);
 	if (percpu) {
 		aux->btf_var.reg_type = PTR_TO_PERCPU_BTF_ID;
+		aux->btf_var.btf = btf_vmlinux;
 		aux->btf_var.btf_id = type;
 	} else if (!btf_type_is_struct(t)) {
 		const struct btf_type *ret;
@@ -9757,6 +9773,7 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
 		aux->btf_var.mem_size = tsize;
 	} else {
 		aux->btf_var.reg_type = PTR_TO_BTF_ID;
+		aux->btf_var.btf = btf_vmlinux;
 		aux->btf_var.btf_id = type;
 	}
 	return 0;
@@ -11609,7 +11626,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 		bpf_log(log, "Tracing programs must provide btf_id\n");
 		return -EINVAL;
 	}
-	btf = tgt_prog ? tgt_prog->aux->btf : btf_vmlinux;
+	btf = tgt_prog ? tgt_prog->aux->btf : prog->aux->attach_btf;
 	if (!btf) {
 		bpf_log(log,
 			"FENTRY/FEXIT program can only be attached to another program annotated with BTF\n");
@@ -11885,7 +11902,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 			return ret;
 	}
 
-	key = bpf_trampoline_compute_key(tgt_prog, btf_id);
+	key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id);
 	tr = bpf_trampoline_get(key, &tgt_info);
 	if (!tr)
 		return -ENOMEM;