From e411901c0b775a3ae7f3e2505f8d2d90ac696178 Mon Sep 17 00:00:00 2001 From: Maciej Fijalkowski Date: Wed, 16 Sep 2020 23:10:09 +0200 Subject: [PATCH] bpf: allow for tailcalls in BPF subprograms for x64 JIT Relax verifier's restriction that was meant to forbid tailcall usage when subprog count was higher than 1. Also, do not max out the stack depth of program that utilizes tailcalls. Signed-off-by: Maciej Fijalkowski Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 172e12df9eaa..d1c009e8c57f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4268,6 +4268,11 @@ static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id) return false; } +static bool allow_tail_call_in_subprogs(struct bpf_verifier_env *env) +{ + return env->prog->jit_requested && IS_ENABLED(CONFIG_X86_64); +} + static int check_map_func_compatibility(struct bpf_verifier_env *env, struct bpf_map *map, int func_id) { @@ -4383,8 +4388,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env, case BPF_FUNC_tail_call: if (map->map_type != BPF_MAP_TYPE_PROG_ARRAY) goto error; - if (env->subprog_cnt > 1) { - verbose(env, "tail_calls are not allowed in programs with bpf-to-bpf calls\n"); + if (env->subprog_cnt > 1 && !allow_tail_call_in_subprogs(env)) { + verbose(env, "tail_calls are not allowed in non-JITed programs with bpf-to-bpf calls\n"); return -EINVAL; } break; @@ -10469,6 +10474,13 @@ static int fixup_call_args(struct bpf_verifier_env *env) return err; } #ifndef CONFIG_BPF_JIT_ALWAYS_ON + if (env->subprog_cnt > 1 && env->prog->aux->tail_call_reachable) { + /* When JIT fails the progs with bpf2bpf calls and tail_calls + * have to be rejected, since interpreter doesn't support them yet. + */ + verbose(env, "tail_calls are not allowed in non-JITed programs with bpf-to-bpf calls\n"); + return -EINVAL; + } for (i = 0; i < prog->len; i++, insn++) { if (insn->code != (BPF_JMP | BPF_CALL) || insn->src_reg != BPF_PSEUDO_CALL) @@ -10632,8 +10644,9 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) * the program array. */ prog->cb_access = 1; - env->prog->aux->stack_depth = MAX_BPF_STACK; - env->prog->aux->max_pkt_offset = MAX_PACKET_OFF; + if (!allow_tail_call_in_subprogs(env)) + prog->aux->stack_depth = MAX_BPF_STACK; + prog->aux->max_pkt_offset = MAX_PACKET_OFF; /* mark bpf_tail_call as different opcode to avoid * conditional branch in the interpeter for every normal