| Message ID | 20230306112138.155352-2-lmb@isovalent.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | BPF |
| Headers | show |
| Series | fix resolving VAR after DATASEC | expand |
On 3/6/23 12:21 PM, Lorenz Bauer wrote: > btf_datasec_resolve contains a bug that causes the following BTF > to fail loading: > > [1] DATASEC a size=2 vlen=2 > type_id=4 offset=0 size=1 > type_id=7 offset=1 size=1 > [2] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none) > [3] PTR (anon) type_id=2 > [4] VAR a type_id=3 linkage=0 > [5] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none) > [6] TYPEDEF td type_id=5 > [7] VAR b type_id=6 linkage=0 > [...] > The fix is to reset resolve_mode to RESOLVE_TBD before attempting to > resolve a VAR from a DATASEC. > > Fixes: 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec") > Signed-off-by: Lorenz Bauer <lmb@isovalent.com> Looks like patchbot is on strike, the series got applied to bpf, thanks!
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index fa22ec79ac0e..73780748404c 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -4569,6 +4569,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env, struct btf *btf = env->btf; u16 i; + env->resolve_mode = RESOLVE_TBD; for_each_vsi_from(i, v->next_member, v->t, vsi) { u32 var_type_id = vsi->type, type_id, type_size = 0; const struct btf_type *var_type = btf_type_by_id(env->btf,
btf_datasec_resolve contains a bug that causes the following BTF to fail loading: [1] DATASEC a size=2 vlen=2 type_id=4 offset=0 size=1 type_id=7 offset=1 size=1 [2] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none) [3] PTR (anon) type_id=2 [4] VAR a type_id=3 linkage=0 [5] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none) [6] TYPEDEF td type_id=5 [7] VAR b type_id=6 linkage=0 This error message is printed during btf_check_all_types: [1] DATASEC a size=2 vlen=2 type_id=7 offset=1 size=1 Invalid type By tracing btf_*_resolve we can pinpoint the problem: btf_datasec_resolve(depth: 1, type_id: 1, mode: RESOLVE_TBD) = 0 btf_var_resolve(depth: 2, type_id: 4, mode: RESOLVE_TBD) = 0 btf_ptr_resolve(depth: 3, type_id: 3, mode: RESOLVE_PTR) = 0 btf_var_resolve(depth: 2, type_id: 4, mode: RESOLVE_PTR) = 0 btf_datasec_resolve(depth: 1, type_id: 1, mode: RESOLVE_PTR) = -22 The last invocation of btf_datasec_resolve should invoke btf_var_resolve by means of env_stack_push, instead it returns EINVAL. The reason is that env_stack_push is never executed for the second VAR. if (!env_type_is_resolve_sink(env, var_type) && !env_type_is_resolved(env, var_type_id)) { env_stack_set_next_member(env, i + 1); return env_stack_push(env, var_type, var_type_id); } env_type_is_resolve_sink() changes its behaviour based on resolve_mode. For RESOLVE_PTR, we can simplify the if condition to the following: (btf_type_is_modifier() || btf_type_is_ptr) && !env_type_is_resolved() Since we're dealing with a VAR the clause evaluates to false. This is not sufficient to trigger the bug however. The log output and EINVAL are only generated if btf_type_id_size() fails. if (!btf_type_id_size(btf, &type_id, &type_size)) { btf_verifier_log_vsi(env, v->t, vsi, "Invalid type"); return -EINVAL; } Most types are sized, so for example a VAR referring to an INT is not a problem. The bug is only triggered if a VAR points at a modifier. Since we skipped btf_var_resolve that modifier was also never resolved, which means that btf_resolved_type_id returns 0 aka VOID for the modifier. This in turn causes btf_type_id_size to return NULL, triggering EINVAL. To summarise, the following conditions are necessary: - VAR pointing at PTR, STRUCT, UNION or ARRAY - Followed by a VAR pointing at TYPEDEF, VOLATILE, CONST, RESTRICT or TYPE_TAG The fix is to reset resolve_mode to RESOLVE_TBD before attempting to resolve a VAR from a DATASEC. Fixes: 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec") Signed-off-by: Lorenz Bauer <lmb@isovalent.com> --- kernel/bpf/btf.c | 1 + 1 file changed, 1 insertion(+)