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KF_RELEASE kfuncs are not currently treated as having KF_TRUSTED_ARGS, even though they have a superset of the requirements of KF_TRUSTED_ARGS. Like KF_TRUSTED_ARGS, KF_RELEASE kfuncs require a 0-offset argument, and don't allow NULL-able arguments. Unlike KF_TRUSTED_ARGS which require _either_ an argument with ref_obj_id > 0, _or_ (ref->type & BPF_REG_TRUSTED_MODIFIERS) (and no unsafe modifiers allowed), KF_RELEASE only allows for ref_obj_id > 0. Because KF_RELEASE today doesn't automatically imply KF_TRUSTED_ARGS, some of these requirements are enforced in different ways that can make the behavior of the verifier feel unpredictable. For example, a KF_RELEASE kfunc with a NULL-able argument will currently fail in the verifier with a message like, "arg#0 is ptr_or_null_ expected ptr_ or socket" rather than "Possibly NULL pointer passed to trusted arg0". Our intention is the same, but the semantics are different due to implemenetation details that kfunc authors and BPF program writers should not need to care about. Let's make the behavior of the verifier more consistent and intuitive by having KF_RELEASE kfuncs imply the presence of KF_TRUSTED_ARGS. Our eventual goal is to have all kfuncs assume KF_TRUSTED_ARGS by default anyways, so this takes us a step in that direction. Note that it does not make sense to assume KF_TRUSTED_ARGS for all KF_ACQUIRE kfuncs. KF_ACQUIRE kfuncs can have looser semantics than KF_RELEASE, with e.g. KF_RCU | KF_RET_NULL. We may want to have KF_ACQUIRE imply KF_TRUSTED_ARGS _unless_ KF_RCU is specified, but that can be left to another patch set, and there are no such subtleties to address for KF_RELEASE. Signed-off-by: David Vernet <void@manifault.com> Link: https://lore.kernel.org/r/20230325213144.486885-4-void@manifault.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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