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bpf: mostly decouple jump history management from is_state_visited()

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Jump history updating and state equivalence checks are conceptually
independent, so move push_jmp_history() out of is_state_visited(). Also
make a decision whether to perform state equivalence checks or not one
layer higher in do_check(), keeping is_state_visited() unconditionally
performing state checks.

push_jmp_history() should be performed after state checks. There is just
one small non-uniformity. When is_state_visited() finds already
validated equivalent state, it propagates precision marks to current
state's parent chain. For this to work correctly, jump history has to be
updated, so is_state_visited() is doing that internally.

But if no equivalent verified state is found, jump history has to be
updated in a newly cloned child state, so is_jmp_point()
+ push_jmp_history() is performed after is_state_visited() exited with
zero result, which means "proceed with validation".

This change has no functional changes. It's not strictly necessary, but
feels right to decouple these two processes.

Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221206233345.438540-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2022-12-06 15:33:44 -08:00 committed by Alexei Starovoitov
parent bffdeaa8a5
commit a095f42105
1 changed files with 26 additions and 23 deletions
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49
kernel/bpf/verifier.c
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@ -13348,13 +13348,6 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
int i, j, err, states_cnt = 0;
bool add_new_state = env->test_state_freq ? true : false;
cur->last_insn_idx = env->prev_insn_idx;
if (!is_prune_point(env, insn_idx))
/* this 'insn_idx' instruction wasn't marked, so we will not
* be doing state search here
*/
return push_jmp_history(env, cur);
/* bpf progs typically have pruning point every 4 instructions
* http://vger.kernel.org/bpfconf2019.html#session-1
* Do not add new state for future pruning if the verifier hasn't seen
@ -13489,10 +13482,10 @@ next:
env->max_states_per_insn = states_cnt;
if (!env->bpf_capable && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
return push_jmp_history(env, cur);
return 0;
if (!add_new_state)
return push_jmp_history(env, cur);
return 0;
/* There were no equivalent states, remember the current one.
* Technically the current state is not proven to be safe yet,
@ -13632,21 +13625,31 @@ static int do_check(struct bpf_verifier_env *env)
return -E2BIG;
}
err = is_state_visited(env, env->insn_idx);
if (err < 0)
return err;
if (err == 1) {
/* found equivalent state, can prune the search */
if (env->log.level & BPF_LOG_LEVEL) {
if (do_print_state)
verbose(env, "\nfrom %d to %d%s: safe\n",
env->prev_insn_idx, env->insn_idx,
env->cur_state->speculative ?
" (speculative execution)" : "");
else
verbose(env, "%d: safe\n", env->insn_idx);
state->last_insn_idx = env->prev_insn_idx;
if (is_prune_point(env, env->insn_idx)) {
err = is_state_visited(env, env->insn_idx);
if (err < 0)
return err;
if (err == 1) {
/* found equivalent state, can prune the search */
if (env->log.level & BPF_LOG_LEVEL) {
if (do_print_state)
verbose(env, "\nfrom %d to %d%s: safe\n",
env->prev_insn_idx, env->insn_idx,
env->cur_state->speculative ?
" (speculative execution)" : "");
else
verbose(env, "%d: safe\n", env->insn_idx);
}
goto process_bpf_exit;
}
goto process_bpf_exit;
}
if (is_jmp_point(env, env->insn_idx)) {
err = push_jmp_history(env, state);
if (err)
return err;
}
if (signal_pending(current))