On Sat, Mar 05, 2022 at 02:18:56AM +0530, Kumar Kartikeya Dwivedi wrote:
> On Sat, Mar 05, 2022 at 01:58:30AM IST, Martin KaFai Lau wrote:
> > > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> > > index 38b24ee8d8c2..7a684050495a 100644
> > > --- a/include/linux/bpf_verifier.h
> > > +++ b/include/linux/bpf_verifier.h
> > > @@ -523,7 +523,8 @@ int check_ptr_off_reg(struct bpf_verifier_env *env,
> > > const struct bpf_reg_state *reg, int regno);
> > > int check_func_arg_reg_off(struct bpf_verifier_env *env,
> > > const struct bpf_reg_state *reg, int regno,
> > > - enum bpf_arg_type arg_type);
> > > + enum bpf_arg_type arg_type,
> > > + bool is_release_function);
> > > int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
> > > u32 regno);
> > > int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
> > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > index 7f6a0ae5028b..c9a1019dc60d 100644
> > > --- a/kernel/bpf/btf.c
> > > +++ b/kernel/bpf/btf.c
> > > @@ -5753,6 +5753,9 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > > return -EINVAL;
> > > }
> > >
> > > + if (is_kfunc)
> > > + rel = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
> > > + BTF_KFUNC_TYPE_RELEASE, func_id);
> > > /* check that BTF function arguments match actual types that the
> > > * verifier sees.
> > > */
> > > @@ -5777,7 +5780,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > > ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
> > > ref_tname = btf_name_by_offset(btf, ref_t->name_off);
> > >
> > > - ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE);
> > > + ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE, rel);
> > > if (ret < 0)
> > > return ret;
> > >
> > > @@ -5809,7 +5812,11 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > > if (reg->type == PTR_TO_BTF_ID) {
> > > reg_btf = reg->btf;
> > > reg_ref_id = reg->btf_id;
> > > - /* Ensure only one argument is referenced PTR_TO_BTF_ID */
> > > + /* Ensure only one argument is referenced
> > > + * PTR_TO_BTF_ID, check_func_arg_reg_off relies
> > > + * on only one referenced register being allowed
> > > + * for kfuncs.
> > > + */
> > > if (reg->ref_obj_id) {
> > > if (ref_obj_id) {
> > > bpf_log(log, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
> > > @@ -5892,8 +5899,6 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > > /* Either both are set, or neither */
> > > WARN_ON_ONCE((ref_obj_id && !ref_regno) || (!ref_obj_id && ref_regno));
> > > if (is_kfunc) {
> > This test is no longer needed?
> >
>
> If you mean the rel && !ref_obj_id below (which is guarded by this check), I do
> think it is needed, why do you think so? Because of the check in
> check_func_arg_reg_off? That only checks reg->off when it sees that both
> release_func and ref_obj_id are true, but ref_obj_id may not be set for any
> argument(s) passed to a release function, so we need to reject when we don't get
> atleast one referenced register for release function.
>
> Or were you referring to the WARN_ON_ONCE above it?
I meant the "if (is_kfunc)" test. rel can only be true
anyway when it is_kfunc.
> > > - rel = btf_kfunc_id_set_contains(btf, resolve_prog_type(env->prog),
> > > - BTF_KFUNC_TYPE_RELEASE, func_id);
> > > /* We already made sure ref_obj_id is set only for one argument */
> > > if (rel && !ref_obj_id) {
> > > bpf_log(log, "release kernel function %s expects refcounted PTR_TO_BTF_ID\n",
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index e55bfd23e81b..c31407d156e7 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -5367,11 +5367,28 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> > >
> > > int check_func_arg_reg_off(struct bpf_verifier_env *env,
> > > const struct bpf_reg_state *reg, int regno,
> > > - enum bpf_arg_type arg_type)
> > > + enum bpf_arg_type arg_type,
> > > + bool is_release_func)
> > > {
> > > enum bpf_reg_type type = reg->type;
> > > + bool fixed_off_ok = false;
> > > int err;
> > >
> > > + /* When referenced PTR_TO_BTF_ID is passed to release function, it's
> > > + * fixed offset must be 0. We rely on the property that only one
> > > + * referenced register can be passed to BPF helpers and kfuncs.
> > > + */
> > > + if (type == PTR_TO_BTF_ID) {
> > > + bool release_reg = is_release_func && reg->ref_obj_id;
> > > +
> > > + if (release_reg && reg->off) {
> > iiuc, the reason for not going through __check_ptr_off_reg() is
> > because it prefers a different verifier log message for release_reg
> > case for fixed off. How about var_off?
> >
>
> If reg->off is zero, we still call __check_ptr_off_reg with fixed_off_ok =
> false, which should handle non-zero var_off.
Understood that __check_ptr_off_reg handles both fixed_off and var_off case.
The question was why only single out reg->off case to have a special message
but not the var_off case. The var_off case does not need a special message?
>
> > > + verbose(env, "R%d must have zero offset when passed to release func\n",
> > > + regno);
> > > + return -EINVAL;
> > > + }
> > > + fixed_off_ok = release_reg ? false : true;
> > nit.
> > fixed_off_ok = !release_reg;
> >
> > but this is a bit moot here considering the reg->off
> > check has already been done for the release_reg case.
> >
>
> Yes, it would be a redundant check inside __check_ptr_off_reg, but we still need
> to call it for checking bad var_off.
Redundant check is fine.
The intention and the net effect here is fixed_off is always
allowed for the remaining case, so may as well directly set
fixed_off_ok to true. "fixed_off_ok = !release_reg;"
made me go back to re-read what else has not been handled
for the release_reg case but it could be just me being
slow here.
It will be useful to at least leave a comment here
on the redundant check and the remaining cases for
PTR_TO_BTF_ID actually always allow fixed_off.
>
> > > + }
> > > +
> > > switch ((u32)type) {
> > > case SCALAR_VALUE:
> > > /* Pointer types where reg offset is explicitly allowed: */
> > > @@ -5394,8 +5411,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
> > > /* All the rest must be rejected: */
> > > default:
> > > force_off_check:
> > > - err = __check_ptr_off_reg(env, reg, regno,
> > > - type == PTR_TO_BTF_ID);
> > > + err = __check_ptr_off_reg(env, reg, regno, fixed_off_ok);
> > > if (err < 0)
> > > return err;
> > > break;
> > > @@ -5452,11 +5468,14 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> > > if (err)
> > > return err;
> > >
> > > - err = check_func_arg_reg_off(env, reg, regno, arg_type);
> > > + err = check_func_arg_reg_off(env, reg, regno, arg_type, is_release_function(meta->func_id));
> > > if (err)
> > > return err;
> > >
> > > skip_type_check:
> > > + /* check_func_arg_reg_off relies on only one referenced register being
> > > + * allowed for BPF helpers.
> > > + */
> > > if (reg->ref_obj_id) {
> > > if (meta->ref_obj_id) {
> > > verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
> > > --
> > > 2.35.1
> > >
>
> --
> Kartikeya
