| Message ID | 20220810165932.2143413-6-roberto.sassu@huawei.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v10,1/9] bpf: Allow kfuncs to be used in LSM programs | expand |
On Wed, Aug 10, 2022 at 7:01 PM Roberto Sassu <roberto.sassu@huawei.com> 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 nit: "with a given key handle serial number" > 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 | 146 +++++++++++++++++++++++++++++++++++++++ > 2 files changed, 152 insertions(+) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index a82f8c559ae2..d415e5e97551 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -2573,4 +2573,10 @@ 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 has_ref; > +}; > +#endif /* CONFIG_KEYS */ > #endif /* _LINUX_BPF_H */ > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 68e5cdd24cef..a607bb0be738 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -20,6 +20,8 @@ > #include <linux/fprobe.h> > #include <linux/bsearch.h> > #include <linux/sort.h> > +#include <linux/key.h> > +#include <linux/verification.h> > > #include <net/bpf_sk_storage.h> > > @@ -1181,6 +1183,150 @@ 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 nit: "key handle serial number" > + * @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. nit: This can be made a little clearer with: Search a key with a given *serial* and the provided *flags*. If found, increment the reference count of the key by one, and return it in the bpf_key structure. > + * 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). The 1 and 2 here are so confusing why not just use their actual names here: KEY_LOOKUP_CREATE and KEY_LOOKUP_PARTIAL. > + * > + * Return: a bpf_key pointer with a valid key pointer if the key is found, a > + * NULL pointer otherwise. > + */ > +struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) > +{ > + key_ref_t key_ref; > + struct bpf_key *bkey; > + > + /* Keep in sync with include/linux/key.h. */ What does this comment mean? Does this mean that more flags may end up in this check? if so, let's just put an inline function in include/linux/key.h? > + if (flags & ~(KEY_LOOKUP_CREATE | KEY_LOOKUP_PARTIAL)) > + return NULL; > + > + /* > + * Permission check is deferred until actual kfunc using the key, > + * since here the intent of the caller is not yet known. > + * > + * We cannot trust the caller to provide the needed permission as > + * argument, since nothing prevents the caller from using the > + * obtained key for a different purpose than the one declared. > + */ nit: This can just be a simple comment. Permission check is deferred until the key is used as the intent of the caller is unknown here. > + key_ref = lookup_user_key(serial, flags, KEY_DEFER_PERM_CHECK); > + if (IS_ERR(key_ref)) > + return NULL; > + > + bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC); > + if (!bkey) { > + key_put(key_ref_to_ptr(key_ref)); > + return NULL; > + } > + > + bkey->key = key_ref_to_ptr(key_ref); > + bkey->has_ref = true; > + > + 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 Please use VERIFY_USE_PLATFORM_KEYRING and VERIFY_USE_SECONDARY_KEYRING here instead of 0 and 1 > + * 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 > + */ > +struct bpf_key *bpf_lookup_system_key(u64 id) > +{ > + struct bpf_key *bkey; > + > + /* Keep in sync with defs in include/linux/verification.h. */ Here too, it's best to introduce a "MAX" value or a small inline helper rather than this comment. > + if (id > (unsigned long)VERIFY_USE_PLATFORM_KEYRING) > + return NULL; > + > + bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC); > + if (!bkey) > + return NULL; > + > + bkey->key = (struct key *)(unsigned long)id; > + bkey->has_ref = 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*. > + */ This is more of a style thing but your comment literally describes the small function below. Do we really need this? > +void bpf_key_put(struct bpf_key *bkey) > +{ > + if (bkey->has_ref) > + key_put(bkey->key); > + > + kfree(bkey); > +} > + > +__diag_pop(); > + > +BTF_SET8_START(key_sig_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) > +BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE) > +BTF_SET8_END(key_sig_kfunc_set) > + > +static const struct btf_kfunc_id_set bpf_key_sig_kfunc_set = { > + .owner = THIS_MODULE, > + .set = &key_sig_kfunc_set, > +}; > + > +static int __init bpf_key_sig_kfuncs_init(void) > +{ > + int ret; > + > + ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, > + &bpf_key_sig_kfunc_set); > + if (!ret) > + return 0; > + > + return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, > + &bpf_key_sig_kfunc_set); > +} > + > +late_initcall(bpf_key_sig_kfuncs_init); > +#endif /* CONFIG_KEYS */ > + > static const struct bpf_func_proto * > bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > { > -- > 2.25.1 > [...]
> From: KP Singh [mailto:kpsingh@kernel.org] > Sent: Friday, August 12, 2022 2:50 AM [...] > > +/** > > + * 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*. > > + */ > > This is more of a style thing but your comment literally describes the > small function > below. Do we really need this? Thanks for the review, KP. Just kept this, to follow the style of kernel documentation for functions. Roberto
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index a82f8c559ae2..d415e5e97551 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2573,4 +2573,10 @@ 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 has_ref; +}; +#endif /* CONFIG_KEYS */ #endif /* _LINUX_BPF_H */ diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 68e5cdd24cef..a607bb0be738 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -20,6 +20,8 @@ #include <linux/fprobe.h> #include <linux/bsearch.h> #include <linux/sort.h> +#include <linux/key.h> +#include <linux/verification.h> #include <net/bpf_sk_storage.h> @@ -1181,6 +1183,150 @@ 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. + */ +struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) +{ + key_ref_t key_ref; + struct bpf_key *bkey; + + /* Keep in sync with include/linux/key.h. */ + if (flags & ~(KEY_LOOKUP_CREATE | KEY_LOOKUP_PARTIAL)) + return NULL; + + /* + * Permission check is deferred until actual kfunc using the key, + * since here the intent of the caller is not yet known. + * + * We cannot trust the caller to provide the needed permission as + * argument, since nothing prevents the caller from using the + * obtained key for a different purpose than the one declared. + */ + key_ref = lookup_user_key(serial, flags, KEY_DEFER_PERM_CHECK); + if (IS_ERR(key_ref)) + return NULL; + + bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC); + if (!bkey) { + key_put(key_ref_to_ptr(key_ref)); + return NULL; + } + + bkey->key = key_ref_to_ptr(key_ref); + bkey->has_ref = true; + + 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 + */ +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_ATOMIC); + if (!bkey) + return NULL; + + bkey->key = (struct key *)(unsigned long)id; + bkey->has_ref = 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*. + */ +void bpf_key_put(struct bpf_key *bkey) +{ + if (bkey->has_ref) + key_put(bkey->key); + + kfree(bkey); +} + +__diag_pop(); + +BTF_SET8_START(key_sig_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) +BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE) +BTF_SET8_END(key_sig_kfunc_set) + +static const struct btf_kfunc_id_set bpf_key_sig_kfunc_set = { + .owner = THIS_MODULE, + .set = &key_sig_kfunc_set, +}; + +static int __init bpf_key_sig_kfuncs_init(void) +{ + int ret; + + ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, + &bpf_key_sig_kfunc_set); + if (!ret) + return 0; + + return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, + &bpf_key_sig_kfunc_set); +} + +late_initcall(bpf_key_sig_kfuncs_init); +#endif /* CONFIG_KEYS */ + static const struct bpf_func_proto * bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) {
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 | 146 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 152 insertions(+)