> From: Kumar Kartikeya Dwivedi [mailto:memxor@xxxxxxxxx] > Sent: Wednesday, July 27, 2022 10:16 AM > Similar to how we detect mem, size pairs in kfunc, teach verifier to > treat __ref suffix on argument name to imply that it must be a trusted > arg when passed to kfunc, similar to the effect of KF_TRUSTED_ARGS flag > but limited to the specific parameter. This is required to ensure that > kfunc that operate on some object only work on acquired pointers and not > normal PTR_TO_BTF_ID with same type which can be obtained by pointer > walking. Release functions need not specify such suffix on release > arguments as they are already expected to receive one referenced > argument. Thanks, Kumar. I will try it. Roberto > Cc: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> > --- > Documentation/bpf/kfuncs.rst | 18 +++++++++++++++++ > kernel/bpf/btf.c | 39 ++++++++++++++++++++++++------------ > net/bpf/test_run.c | 9 +++++++-- > 3 files changed, 51 insertions(+), 15 deletions(-) > > diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst > index c0b7dae6dbf5..41dff6337446 100644 > --- a/Documentation/bpf/kfuncs.rst > +++ b/Documentation/bpf/kfuncs.rst > @@ -72,6 +72,24 @@ argument as its size. By default, without __sz annotation, > the size of the type > of the pointer is used. Without __sz annotation, a kfunc cannot accept a void > pointer. > > +2.2.2 __ref Annotation > +---------------------- > + > +This annotation is used to indicate that the argument is trusted, i.e. it will > +be a pointer from an acquire function (defined later), and its offset will be > +zero. This annotation has the same effect as the KF_TRUSTED_ARGS kfunc flag > but > +only on the parameter it is applied to. An example is shown below:: > + > + void bpf_task_send_signal(struct task_struct *task__ref, int signal) > + { > + ... > + } > + > +Here, bpf_task_send_signal will only act on trusted task_struct pointers, and > +cannot be used on pointers obtained using pointer walking. This ensures that > +caller always calls this kfunc on a task whose lifetime is guaranteed for the > +duration of the call. > + > .. _BPF_kfunc_nodef: > > 2.3 Using an existing kernel function > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > index 7ac971ea98d1..3ce9b2deef9c 100644 > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -6141,18 +6141,13 @@ static bool __btf_type_is_scalar_struct(struct > bpf_verifier_log *log, > return true; > } > > -static bool is_kfunc_arg_mem_size(const struct btf *btf, > - const struct btf_param *arg, > - const struct bpf_reg_state *reg) > +static bool btf_param_match_suffix(const struct btf *btf, > + const struct btf_param *arg, > + const char *suffix) > { > - int len, sfx_len = sizeof("__sz") - 1; > - const struct btf_type *t; > + int len, sfx_len = strlen(suffix); > const char *param_name; > > - t = btf_type_skip_modifiers(btf, arg->type, NULL); > - if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE) > - return false; > - > /* In the future, this can be ported to use BTF tagging */ > param_name = btf_name_by_offset(btf, arg->name_off); > if (str_is_empty(param_name)) > @@ -6161,10 +6156,26 @@ static bool is_kfunc_arg_mem_size(const struct btf > *btf, > if (len < sfx_len) > return false; > param_name += len - sfx_len; > - if (strncmp(param_name, "__sz", sfx_len)) > + return !strncmp(param_name, suffix, sfx_len); > +} > + > +static bool is_kfunc_arg_ref(const struct btf *btf, > + const struct btf_param *arg) > +{ > + return btf_param_match_suffix(btf, arg, "__ref"); > +} > + > +static bool is_kfunc_arg_mem_size(const struct btf *btf, > + const struct btf_param *arg, > + const struct bpf_reg_state *reg) > +{ > + const struct btf_type *t; > + > + t = btf_type_skip_modifiers(btf, arg->type, NULL); > + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE) > return false; > > - return true; > + return btf_param_match_suffix(btf, arg, "__sz"); > } > > static int btf_check_func_arg_match(struct bpf_verifier_env *env, > @@ -6174,7 +6185,7 @@ static int btf_check_func_arg_match(struct > bpf_verifier_env *env, > u32 kfunc_flags) > { > enum bpf_prog_type prog_type = resolve_prog_type(env->prog); > - bool rel = false, kptr_get = false, trusted_arg = false; > + bool rel = false, kptr_get = false, kf_trusted_args = false; > struct bpf_verifier_log *log = &env->log; > u32 i, nargs, ref_id, ref_obj_id = 0; > bool is_kfunc = btf_is_kernel(btf); > @@ -6211,7 +6222,7 @@ static int btf_check_func_arg_match(struct > bpf_verifier_env *env, > /* Only kfunc can be release func */ > rel = kfunc_flags & KF_RELEASE; > kptr_get = kfunc_flags & KF_KPTR_GET; > - trusted_arg = kfunc_flags & KF_TRUSTED_ARGS; > + kf_trusted_args = kfunc_flags & KF_TRUSTED_ARGS; > } > > /* check that BTF function arguments match actual types that the > @@ -6221,6 +6232,7 @@ static int btf_check_func_arg_match(struct > bpf_verifier_env *env, > enum bpf_arg_type arg_type = ARG_DONTCARE; > u32 regno = i + 1; > struct bpf_reg_state *reg = ®s[regno]; > + bool trusted_arg = false; > > t = btf_type_skip_modifiers(btf, args[i].type, NULL); > if (btf_type_is_scalar(t)) { > @@ -6239,6 +6251,7 @@ static int btf_check_func_arg_match(struct > bpf_verifier_env *env, > /* Check if argument must be a referenced pointer, args + i has > * been verified to be a pointer (after skipping modifiers). > */ > + trusted_arg = kf_trusted_args || is_kfunc_arg_ref(btf, args + i); > if (is_kfunc && trusted_arg && !reg->ref_obj_id) { > bpf_log(log, "R%d must be referenced\n", regno); > return -EINVAL; > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > index cbc9cd5058cb..247bfe52e585 100644 > --- a/net/bpf/test_run.c > +++ b/net/bpf/test_run.c > @@ -691,7 +691,11 @@ noinline void bpf_kfunc_call_test_mem_len_fail2(u64 > *mem, int len) > { > } > > -noinline void bpf_kfunc_call_test_ref(struct prog_test_ref_kfunc *p) > +noinline void bpf_kfunc_call_test_trusted(struct prog_test_ref_kfunc *p) > +{ > +} > + > +noinline void bpf_kfunc_call_test_ref(struct prog_test_ref_kfunc *p__ref) > { > } > > @@ -718,7 +722,8 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_test_fail3) > BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_pass1) > BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail1) > BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail2) > -BTF_ID_FLAGS(func, bpf_kfunc_call_test_ref, KF_TRUSTED_ARGS) > +BTF_ID_FLAGS(func, bpf_kfunc_call_test_trusted, KF_TRUSTED_ARGS) > +BTF_ID_FLAGS(func, bpf_kfunc_call_test_ref) > BTF_SET8_END(test_sk_check_kfunc_ids) > > static void *bpf_test_init(const union bpf_attr *kattr, u32 user_size, > -- > 2.34.1
