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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 <maciej.fijalkowski@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Maciej Fijalkowski 2020-09-16 23:10:09 +02:00 committed by Alexei Starovoitov
parent ebf7d1f508
commit e411901c0b
1 changed files with 17 additions and 4 deletions
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21
kernel/bpf/verifier.c
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@ -4268,6 +4268,11 @@ static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id)
return false; 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, static int check_map_func_compatibility(struct bpf_verifier_env *env,
struct bpf_map *map, int func_id) 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: case BPF_FUNC_tail_call:
if (map->map_type != BPF_MAP_TYPE_PROG_ARRAY) if (map->map_type != BPF_MAP_TYPE_PROG_ARRAY)
goto error; goto error;
if (env->subprog_cnt > 1) { if (env->subprog_cnt > 1 && !allow_tail_call_in_subprogs(env)) {
verbose(env, "tail_calls are not allowed in programs with bpf-to-bpf calls\n"); verbose(env, "tail_calls are not allowed in non-JITed programs with bpf-to-bpf calls\n");
return -EINVAL; return -EINVAL;
} }
break; break;
@ -10469,6 +10474,13 @@ static int fixup_call_args(struct bpf_verifier_env *env)
return err; return err;
} }
#ifndef CONFIG_BPF_JIT_ALWAYS_ON #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++) { for (i = 0; i < prog->len; i++, insn++) {
if (insn->code != (BPF_JMP | BPF_CALL) || if (insn->code != (BPF_JMP | BPF_CALL) ||
insn->src_reg != BPF_PSEUDO_CALL) insn->src_reg != BPF_PSEUDO_CALL)
@ -10632,8 +10644,9 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
* the program array. * the program array.
*/ */
prog->cb_access = 1; prog->cb_access = 1;
env->prog->aux->stack_depth = MAX_BPF_STACK; if (!allow_tail_call_in_subprogs(env))
env->prog->aux->max_pkt_offset = MAX_PACKET_OFF; prog->aux->stack_depth = MAX_BPF_STACK;
prog->aux->max_pkt_offset = MAX_PACKET_OFF;
/* mark bpf_tail_call as different opcode to avoid /* mark bpf_tail_call as different opcode to avoid
* conditional branch in the interpeter for every normal * conditional branch in the interpeter for every normal