Nothing changes for systems that do not use the bpf keyring. Without bpf.keyring_unsealed=1 a caller-supplied keyring behaves exactly as before, which also lets it serve as the staging step for software installed onto a running system whose signing key is not enrolled anywhere yet. Passing bpf.keyring_unsealed=1 states that the bpf keyring is the trust anchor for this boot, so from the first program load onwards a caller- supplied keyring is refused with -EPERM. Deriving this from the boot flag rather than from the keyring's runtime state keeps the decision immutable from userspace. Signed-off-by: Daniel Borkmann --- Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ include/linux/bpf.h | 6 ++++++ kernel/bpf/keys.c | 5 +++++ kernel/bpf/verifier.c | 10 +++++++--- 4 files changed, 26 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2beb61092bb3..e70fb15757d4 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -673,6 +673,14 @@ Kernel parameters keys. Once the keyring is restricted it becomes active and can be used for BPF program signature verification. + Setting this also means that the bpf keyring is the + only non-system keyring a loader may select for the + rest of the boot: caller-supplied user/session + keyrings are refused with -EPERM, whether or not + provisioning actually completed. The system keyrings + stay selectable. Leaving it unset keeps the prior + behaviour, where a caller-supplied keyring is allowed. + See Documentation/bpf/signing.rst bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 039674b2f875..3a7eb2185c35 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -3821,6 +3821,7 @@ struct bpf_key { struct bpf_key *bpf_lookup_user_key(s32 serial, u64 flags); struct bpf_key *bpf_lookup_system_key(u64 id); struct bpf_key *bpf_lookup_keyring(void); +bool bpf_keyring_enforced(void); void bpf_key_put(struct bpf_key *bkey); int bpf_verify_pkcs7_signature(const struct bpf_dynptr *data_p, const struct bpf_dynptr *sig_p, @@ -3846,6 +3847,11 @@ static inline struct bpf_key *bpf_lookup_keyring(void) return NULL; } +static inline bool bpf_keyring_enforced(void) +{ + return false; +} + static inline void bpf_key_put(struct bpf_key *bkey) { } diff --git a/kernel/bpf/keys.c b/kernel/bpf/keys.c index 08549b3220c1..bffc356839ac 100644 --- a/kernel/bpf/keys.c +++ b/kernel/bpf/keys.c @@ -18,6 +18,11 @@ static bool bpf_keyring_unsealed __ro_after_init; module_param_named(keyring_unsealed, bpf_keyring_unsealed, bool, 0444); MODULE_PARM_DESC(keyring_unsealed, "Leave the bpf keyring unsealed"); +bool bpf_keyring_enforced(void) +{ + return bpf_keyring_unsealed; +} + struct bpf_key *bpf_lookup_keyring(void) { struct bpf_key *bkey; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9c6624d2f5fb..2d50adf3800d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -21019,12 +21019,16 @@ static int bpf_prog_verify_signature(struct bpf_verifier_env *env, if (!attr->signature_size || attr->signature_size > KMALLOC_MAX_CACHE_SIZE) return -EINVAL; - if (system_keyring_id_check(attr->keyring_id) == 0) + if (system_keyring_id_check(attr->keyring_id) == 0) { key = bpf_lookup_system_key(attr->keyring_id); - else if (attr->keyring_id == KEY_SPEC_BPF_KEYRING) + } else if (attr->keyring_id == KEY_SPEC_BPF_KEYRING) { key = bpf_lookup_keyring(); - else + } else if (bpf_keyring_enforced()) { + verbose(env, "caller-supplied keyring refused, use bpf keyring\n"); + return -EPERM; + } else { key = bpf_lookup_user_key(attr->keyring_id, 0); + } if (!key) { if (attr->keyring_id == KEY_SPEC_BPF_KEYRING) { verbose(env, "the bpf keyring is empty or has not been restricted\n"); -- 2.43.0