bpf: Remove superfluous aux sanitation on subprog rejection

Follow-up to fe9a5ca7e370 ("bpf: Do not mark insn as seen under speculative
path verification"). The sanitize_insn_aux_data() helper does not serve a
particular purpose in today's code. The original intention for the helper
was that if function-by-function verification fails, a given program would
be cleared from temporary insn_aux_data[], and then its verification would
be re-attempted in the context of the main program a second time.

However, a failure in do_check_subprogs() will skip do_check_main() and
propagate the error to the user instead, thus such situation can never occur.
Given its interaction is not compatible to the Spectre v1 mitigation (due to
comparing aux->seen with env->pass_cnt), just remove sanitize_insn_aux_data()
to avoid future bugs in this area.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9de3c9c3267cb10ddcaf1070defea4930dfbb596..8a7a28b4cfb9255dd0de729be267bf2919f0f502 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12752,37 +12752,6 @@ static void free_states(struct bpf_verifier_env *env)
        }
 }
 
-/* The verifier is using insn_aux_data[] to store temporary data during
- * verification and to store information for passes that run after the
- * verification like dead code sanitization. do_check_common() for subprogram N
- * may analyze many other subprograms. sanitize_insn_aux_data() clears all
- * temporary data after do_check_common() finds that subprogram N cannot be
- * verified independently. pass_cnt counts the number of times
- * do_check_common() was run and insn->aux->seen tells the pass number
- * insn_aux_data was touched. These variables are compared to clear temporary
- * data from failed pass. For testing and experiments do_check_common() can be
- * run multiple times even when prior attempt to verify is unsuccessful.
- *
- * Note that special handling is needed on !env->bypass_spec_v1 if this is
- * ever called outside of error path with subsequent program rejection.
- */
-static void sanitize_insn_aux_data(struct bpf_verifier_env *env)
-{
-       struct bpf_insn *insn = env->prog->insnsi;
-       struct bpf_insn_aux_data *aux;
-       int i, class;
-
-       for (i = 0; i < env->prog->len; i++) {
-               class = BPF_CLASS(insn[i].code);
-               if (class != BPF_LDX && class != BPF_STX)
-                       continue;
-               aux = &env->insn_aux_data[i];
-               if (aux->seen != env->pass_cnt)
-                       continue;
-               memset(aux, 0, offsetof(typeof(*aux), orig_idx));
-       }
-}
-
 static int do_check_common(struct bpf_verifier_env *env, int subprog)
 {
        bool pop_log = !(env->log.level & BPF_LOG_LEVEL2);
@@ -12859,9 +12828,6 @@ out:
        if (!ret && pop_log)
                bpf_vlog_reset(&env->log, 0);
        free_states(env);
-       if (ret)
-               /* clean aux data in case subprog was rejected */
-               sanitize_insn_aux_data(env);
        return ret;
 }