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

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... 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: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Reviewed-by: Benedict Schlueter <benedict.schlueter@rub.de>
Reviewed-by: Piotr Krysiuk <piotras@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2021-05-28 13:47:27 +00:00
parent d203b0fd86
commit fe9a5ca7e3
1 changed files with 18 additions and 2 deletions
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20
kernel/bpf/verifier.c
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@ -6572,6 +6572,19 @@ do_sim:
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 @@ process_bpf_exit:
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)
{