Messages in this thread | | | Subject | Re: [PATCH v9 06/10] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs | From | Daniel Borkmann <> | Date | Wed, 10 Aug 2022 00:53:21 +0200 |
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On 8/9/22 3:45 PM, Roberto Sassu wrote: > Add the bpf_lookup_user_key(), bpf_lookup_system_key() and bpf_key_put() > kfuncs, to respectively search a key with a given serial and flags, obtain > a key from a pre-determined ID defined in include/linux/verification.h, and > cleanup. > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > --- > include/linux/bpf.h | 6 ++ > kernel/trace/bpf_trace.c | 151 +++++++++++++++++++++++++++++++++++++++ > 2 files changed, 157 insertions(+) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index 0d56c23cc504..564b9e0b8c16 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -2572,4 +2572,10 @@ static inline void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype) {} > static inline void bpf_cgroup_atype_put(int cgroup_atype) {} > #endif /* CONFIG_BPF_LSM */ > > +#ifdef CONFIG_KEYS > +struct bpf_key { > + struct key *key; > + bool valid_ptr; > +}; > +#endif /* CONFIG_KEYS */ > #endif /* _LINUX_BPF_H */ > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 68e5cdd24cef..33ca4cfe6e26 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -20,6 +20,7 @@ > #include <linux/fprobe.h> > #include <linux/bsearch.h> > #include <linux/sort.h> > +#include <linux/key.h> > > #include <net/bpf_sk_storage.h> > > @@ -1181,6 +1182,156 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = { > .arg1_type = ARG_PTR_TO_CTX, > }; > > +#ifdef CONFIG_KEYS > +__diag_push(); > +__diag_ignore_all("-Wmissing-prototypes", > + "kfuncs which will be used in BPF programs"); > + > +/** > + * bpf_lookup_user_key - lookup a key by its serial > + * @serial: key serial > + * @flags: lookup-specific flags > + * > + * Search a key with a given *serial* and the provided *flags*. The > + * returned key, if found, has the reference count incremented by > + * one, and is stored in a bpf_key structure, returned to the caller. > + * The bpf_key structure must be passed to bpf_key_put() when done > + * with it, so that the key reference count is decremented and the > + * bpf_key structure is freed. > + * > + * Permission checks are deferred to the time the key is used by > + * one of the available key-specific kfuncs. > + * > + * Set *flags* with 1, to attempt creating a requested special > + * keyring (e.g. session keyring), if it doesn't yet exist. Set > + * *flags* with 2 to lookup a key without waiting for the key > + * construction, and to retrieve uninstantiated keys (keys without > + * data attached to them). > + * > + * Return: a bpf_key pointer with a valid key pointer if the key is found, a > + * NULL pointer otherwise. > + */ > +noinline __weak struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags)
Why the need for noinline and the __weak here and below? (If indeed needed this should probably be explained in the commit desc.)
> +{ > + key_ref_t key_ref; > + struct bpf_key *bkey; > + > + /* Keep in sync with include/linux/key.h. */ > + if (flags > (KEY_LOOKUP_PARTIAL << 1) - 1)
Can't we just simplify and test flags & ~(KEY_LOOKUP_CREATE|KEY_LOOKUP_PARTIAL)?
> + return NULL; > + > + /* Permission check is deferred until actual kfunc using the key. */ > + key_ref = lookup_user_key(serial, flags, KEY_DEFER_PERM_CHECK); > + if (IS_ERR(key_ref)) > + return NULL; > + > + bkey = kmalloc(sizeof(*bkey), GFP_KERNEL); > + if (!bkey) { > + key_put(key_ref_to_ptr(key_ref)); > + return bkey;
nit: just return NULL probably cleaner
> + } > + > + bkey->key = key_ref_to_ptr(key_ref); > + bkey->valid_ptr = true;
nit: I'd probably rename s/valid_ptr/has_ref/.
> + return bkey; > +} > + > +/** > + * bpf_lookup_system_key - lookup a key by a system-defined ID > + * @id: key ID > + * > + * Obtain a bpf_key structure with a key pointer set to the passed key ID. > + * The key pointer is marked as invalid, to prevent bpf_key_put() from > + * attempting to decrement the key reference count on that pointer. The key > + * pointer set in such way is currently understood only by > + * verify_pkcs7_signature(). > + * > + * Set *id* to one of the values defined in include/linux/verification.h: > + * 0 for the primary keyring (immutable keyring of system keys); 1 for both > + * the primary and secondary keyring (where keys can be added only if they > + * are vouched for by existing keys in those keyrings); 2 for the platform > + * keyring (primarily used by the integrity subsystem to verify a kexec'ed > + * kerned image and, possibly, the initramfs signature). > + * > + * Return: a bpf_key pointer with an invalid key pointer set from the > + * pre-determined ID on success, a NULL pointer otherwise > + */ > +noinline __weak struct bpf_key *bpf_lookup_system_key(u64 id) > +{ > + struct bpf_key *bkey; > + > + /* Keep in sync with defs in include/linux/verification.h. */ > + if (id > (unsigned long)VERIFY_USE_PLATFORM_KEYRING) > + return NULL; > + > + bkey = kmalloc(sizeof(*bkey), GFP_KERNEL);
nit: Can't this be GFP_ATOMIC? Then bpf_lookup_system_key doesn't need KF_SLEEPABLE attribute, fwiw. Overall, the bpf_lookup_{system,user}_key() look reasonable.
> + if (!bkey) > + return bkey; > + > + bkey->key = (struct key *)(unsigned long)id; > + bkey->valid_ptr = false; > + > + return bkey; > +} > + > +/** > + * bpf_key_put - decrement key reference count if key is valid and free bpf_key > + * @bkey: bpf_key structure > + * > + * Decrement the reference count of the key inside *bkey*, if the pointer > + * is valid, and free *bkey*. > + */ > +noinline __weak void bpf_key_put(struct bpf_key *bkey) > +{ > + if (bkey->valid_ptr) > + key_put(bkey->key); > + > + kfree(bkey); > +} > + > +__diag_pop(); > + > +BTF_SET8_START(key_kfunc_set) > +BTF_ID_FLAGS(func, bpf_lookup_user_key, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE) > +BTF_ID_FLAGS(func, bpf_lookup_system_key, > + KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE) > +BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE) > +BTF_SET8_END(key_kfunc_set) > + > +static const struct btf_kfunc_id_set bpf_key_kfunc_set = { > + .owner = THIS_MODULE, > + .set = &key_kfunc_set, > +}; > +#endif /* CONFIG_KEYS */ > + > +const struct btf_kfunc_id_set *kfunc_sets[] = { > +#ifdef CONFIG_KEYS > + &bpf_key_kfunc_set, > +#endif /* CONFIG_KEYS */ > +};
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