Commit fe9a5ca7 authored by Daniel Borkmann's avatar Daniel Borkmann
Browse files

bpf: Do not mark insn as seen under speculative path verification 



... in such circumstances, we do not want to mark the instruction as seen given
the goal is still to jmp-1 rewrite/sanitize dead code, if it is not reachable
from the non-speculative path verification. We do however want to verify it for
safety regardless.

With the patch as-is all the insns that have been marked as seen before the
patch will also be marked as seen after the patch (just with a potentially
different non-zero count). An upcoming patch will also verify paths that are
unreachable in the non-speculative domain, hence this extension is needed.

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Reviewed-by: default avatarBenedict Schlueter <benedict.schlueter@rub.de>
Reviewed-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent d203b0fd

kernel/bpf/verifier.c

+18 −2
Original line number Diff line number Diff line
@@ -6572,6 +6572,19 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, 
	return !ret ? REASON_STACK : 0;

}



static void sanitize_mark_insn_seen(struct bpf_verifier_env *env)

{

	struct bpf_verifier_state *vstate = env->cur_state;



	/* If we simulate paths under speculation, we don't update the

	 * insn as 'seen' such that when we verify unreachable paths in

	 * the non-speculative domain, sanitize_dead_code() can still

	 * rewrite/sanitize them.

	 */

	if (!vstate->speculative)

		env->insn_aux_data[env->insn_idx].seen = env->pass_cnt;

}



static int sanitize_err(struct bpf_verifier_env *env,

			const struct bpf_insn *insn, int reason,

			const struct bpf_reg_state *off_reg,
@@ -10630,7 +10643,7 @@ static int do_check(struct bpf_verifier_env *env) 
		}



		regs = cur_regs(env);

		env->insn_aux_data[env->insn_idx].seen = env->pass_cnt;

		sanitize_mark_insn_seen(env);

		prev_insn_idx = env->insn_idx;



		if (class == BPF_ALU || class == BPF_ALU64) {
@@ -10857,7 +10870,7 @@ static int do_check(struct bpf_verifier_env *env) 
					return err;



				env->insn_idx++;

				env->insn_aux_data[env->insn_idx].seen = env->pass_cnt;

				sanitize_mark_insn_seen(env);

			} else {

				verbose(env, "invalid BPF_LD mode\n");

				return -EINVAL;
@@ -12712,6 +12725,9 @@ static void free_states(struct bpf_verifier_env *env) 
 * 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)

{