From 09b28d76eac48e922dc293da1aa2b2b85c32aeee Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 17 Sep 2020 19:09:18 -0700 Subject: [PATCH] bpf: Add abnormal return checks. LD_[ABS|IND] instructions may return from the function early. bpf_tail_call pseudo instruction is either fallthrough or return. Allow them in the subprograms only when subprograms are BTF annotated and have scalar return types. Allow ld_abs and tail_call in the main program even if it calls into subprograms. In the past that was not ok to do for ld_abs, since it was JITed with special exit sequence. Since bpf_gen_ld_abs() was introduced the ld_abs looks like normal exit insn from JIT point of view, so it's safe to allow them in the main program. Signed-off-by: Alexei Starovoitov --- include/linux/bpf_verifier.h | 1 + kernel/bpf/verifier.c | 67 ++++++++++++++------ tools/testing/selftests/bpf/verifier/calls.c | 6 +- 3 files changed, 52 insertions(+), 22 deletions(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index fbc964526ba3..2bb48a2c4d08 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -360,6 +360,7 @@ struct bpf_subprog_info { u16 stack_depth; /* max. stack depth used by this function */ bool has_tail_call; bool tail_call_reachable; + bool has_ld_abs; }; /* single container for all structs diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d1c009e8c57f..4161b6c406bc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1494,6 +1494,9 @@ static int check_subprogs(struct bpf_verifier_env *env) insn[i].imm == BPF_FUNC_tail_call && insn[i].src_reg != BPF_PSEUDO_CALL) subprog[cur_subprog].has_tail_call = true; + if (BPF_CLASS(code) == BPF_LD && + (BPF_MODE(code) == BPF_ABS || BPF_MODE(code) == BPF_IND)) + subprog[cur_subprog].has_ld_abs = true; if (BPF_CLASS(code) != BPF_JMP && BPF_CLASS(code) != BPF_JMP32) goto next; if (BPF_OP(code) == BPF_EXIT || BPF_OP(code) == BPF_CALL) @@ -7514,18 +7517,6 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn) return -EINVAL; } - if (env->subprog_cnt > 1) { - /* when program has LD_ABS insn JITs and interpreter assume - * that r1 == ctx == skb which is not the case for callees - * that can have arbitrary arguments. It's problematic - * for main prog as well since JITs would need to analyze - * all functions in order to make proper register save/restore - * decisions in the main prog. Hence disallow LD_ABS with calls - */ - verbose(env, "BPF_LD_[ABS|IND] instructions cannot be mixed with bpf-to-bpf calls\n"); - return -EINVAL; - } - if (insn->dst_reg != BPF_REG_0 || insn->off != 0 || BPF_SIZE(insn->code) == BPF_DW || (mode == BPF_ABS && insn->src_reg != BPF_REG_0)) { @@ -7936,6 +7927,23 @@ static int check_cfg(struct bpf_verifier_env *env) return ret; } +static int check_abnormal_return(struct bpf_verifier_env *env) +{ + int i; + + for (i = 1; i < env->subprog_cnt; i++) { + if (env->subprog_info[i].has_ld_abs) { + verbose(env, "LD_ABS is not allowed in subprogs without BTF\n"); + return -EINVAL; + } + if (env->subprog_info[i].has_tail_call) { + verbose(env, "tail_call is not allowed in subprogs without BTF\n"); + return -EINVAL; + } + } + return 0; +} + /* The minimum supported BTF func info size */ #define MIN_BPF_FUNCINFO_SIZE 8 #define MAX_FUNCINFO_REC_SIZE 252 @@ -7944,20 +7952,24 @@ static int check_btf_func(struct bpf_verifier_env *env, const union bpf_attr *attr, union bpf_attr __user *uattr) { + const struct btf_type *type, *func_proto, *ret_type; u32 i, nfuncs, urec_size, min_size; u32 krec_size = sizeof(struct bpf_func_info); struct bpf_func_info *krecord; struct bpf_func_info_aux *info_aux = NULL; - const struct btf_type *type; struct bpf_prog *prog; const struct btf *btf; void __user *urecord; u32 prev_offset = 0; + bool scalar_return; int ret = -ENOMEM; nfuncs = attr->func_info_cnt; - if (!nfuncs) + if (!nfuncs) { + if (check_abnormal_return(env)) + return -EINVAL; return 0; + } if (nfuncs != env->subprog_cnt) { verbose(env, "number of funcs in func_info doesn't match number of subprogs\n"); @@ -8005,25 +8017,23 @@ static int check_btf_func(struct bpf_verifier_env *env, } /* check insn_off */ + ret = -EINVAL; if (i == 0) { if (krecord[i].insn_off) { verbose(env, "nonzero insn_off %u for the first func info record", krecord[i].insn_off); - ret = -EINVAL; goto err_free; } } else if (krecord[i].insn_off <= prev_offset) { verbose(env, "same or smaller insn offset (%u) than previous func info record (%u)", krecord[i].insn_off, prev_offset); - ret = -EINVAL; goto err_free; } if (env->subprog_info[i].start != krecord[i].insn_off) { verbose(env, "func_info BTF section doesn't match subprog layout in BPF program\n"); - ret = -EINVAL; goto err_free; } @@ -8032,10 +8042,26 @@ static int check_btf_func(struct bpf_verifier_env *env, if (!type || !btf_type_is_func(type)) { verbose(env, "invalid type id %d in func info", krecord[i].type_id); - ret = -EINVAL; goto err_free; } info_aux[i].linkage = BTF_INFO_VLEN(type->info); + + func_proto = btf_type_by_id(btf, type->type); + if (unlikely(!func_proto || !btf_type_is_func_proto(func_proto))) + /* btf_func_check() already verified it during BTF load */ + goto err_free; + ret_type = btf_type_skip_modifiers(btf, func_proto->type, NULL); + scalar_return = + btf_type_is_small_int(ret_type) || btf_type_is_enum(ret_type); + if (i && !scalar_return && env->subprog_info[i].has_ld_abs) { + verbose(env, "LD_ABS is only allowed in functions that return 'int'.\n"); + goto err_free; + } + if (i && !scalar_return && env->subprog_info[i].has_tail_call) { + verbose(env, "tail_call is only allowed in functions that return 'int'.\n"); + goto err_free; + } + prev_offset = krecord[i].insn_off; urecord += urec_size; } @@ -8196,8 +8222,11 @@ static int check_btf_info(struct bpf_verifier_env *env, struct btf *btf; int err; - if (!attr->func_info_cnt && !attr->line_info_cnt) + if (!attr->func_info_cnt && !attr->line_info_cnt) { + if (check_abnormal_return(env)) + return -EINVAL; return 0; + } btf = btf_get_by_fd(attr->prog_btf_fd); if (IS_ERR(btf)) diff --git a/tools/testing/selftests/bpf/verifier/calls.c b/tools/testing/selftests/bpf/verifier/calls.c index 94258c6b5235..c4f5d909e58a 100644 --- a/tools/testing/selftests/bpf/verifier/calls.c +++ b/tools/testing/selftests/bpf/verifier/calls.c @@ -647,13 +647,14 @@ .result = REJECT, }, { - "calls: ld_abs with changing ctx data in callee", + "calls: subprog call with ld_abs in main prog", .insns = { BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), BPF_LD_ABS(BPF_B, 0), BPF_LD_ABS(BPF_H, 0), BPF_LD_ABS(BPF_W, 0), BPF_MOV64_REG(BPF_REG_7, BPF_REG_6), + BPF_MOV64_REG(BPF_REG_1, BPF_REG_6), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, 5), BPF_MOV64_REG(BPF_REG_6, BPF_REG_7), BPF_LD_ABS(BPF_B, 0), @@ -666,8 +667,7 @@ BPF_EXIT_INSN(), }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, - .errstr = "BPF_LD_[ABS|IND] instructions cannot be mixed", - .result = REJECT, + .result = ACCEPT, }, { "calls: two calls with bad fallthrough",