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Hallyn" , Mauro Carvalho Chehab , "David S. Miller" , Nicolas Ferre , Stanislav Fomichev , Quentin Monnet , Andrey Ignatov , Joe Stringer Subject: [PATCH bpf-next v3 06/10] bpf: lsm: Implement attach, detach and execution Date: Thu, 23 Jan 2020 07:24:36 -0800 Message-Id: <20200123152440.28956-7-kpsingh@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200123152440.28956-1-kpsingh@chromium.org> References: <20200123152440.28956-1-kpsingh@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: KP Singh JITed BPF programs are used by the BPF LSM as dynamically allocated security hooks. arch_bpf_prepare_trampoline generates code to handle conversion of the signature of the hook to the BPF context and allows the BPF program to be called directly as a C function. The BPF_PROG_TYPE_LSM programs must have a GPL compatible license and the following permissions are required to attach a program to a hook: - CAP_SYS_ADMIN to load the program - CAP_MAC_ADMIN to attach it (i.e. to update the security policy) When the program is loaded (BPF_PROG_LOAD), the verifier receives the index of the member in the security_hook_heads struct in the prog->aux->lsm_hook_idx and uses the BTF API provided by the LSM to: - Populate the name of the hook in prog->aux->attach_func_name and the prototype in prog->aux->attach_func_proto. - Verify if the offset is valid for a type struct hlist_head. - The program is verified for accesses based on the attach_func_proto similar to raw_tp BPF programs. When an attachment (BPF_PROG_ATTACH) is requested: - The information required to set-up of a callback is populated in the struct bpf_lsm_list. - A new callback and a bpf_lsm_hook is allocated and the address of the hook is set to the be the address of the allocated callback. - The attachment returns an anonymous O_CLOEXEC fd which detaches the program on close. Signed-off-by: KP Singh Reviewed-by: Brendan Jackman Reviewed-by: Florent Revest Reviewed-by: Greg Kroah-Hartman Reviewed-by: Thomas Garnier --- include/linux/bpf.h | 4 + include/linux/bpf_lsm.h | 15 +++ include/uapi/linux/bpf.h | 4 + kernel/bpf/syscall.c | 47 +++++++- kernel/bpf/verifier.c | 73 ++++++++++-- security/bpf/Kconfig | 1 + security/bpf/hooks.c | 201 +++++++++++++++++++++++++++++++++ security/bpf/include/bpf_lsm.h | 49 ++++++++ security/bpf/lsm.c | 19 ++++ security/bpf/ops.c | 2 + tools/include/uapi/linux/bpf.h | 4 + 11 files changed, 408 insertions(+), 11 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index a9687861fd7e..6d6653a375f6 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -614,6 +614,10 @@ struct bpf_prog_aux { u32 func_cnt; /* used by non-func prog as the number of func progs */ u32 func_idx; /* 0 for non-func prog, the index in func array for func prog */ u32 attach_btf_id; /* in-kernel BTF type id to attach to */ + /* Index of the hlist_head in security_hook_heads to which the program + * must be attached. + */ + u32 lsm_hook_idx; struct bpf_prog *linked_prog; bool verifier_zext; /* Zero extensions has been inserted by verifier. */ bool offload_requested; diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 5e61c0736001..b6daa0875c8d 100644 --- a/include/linux/bpf_lsm.h +++ b/include/linux/bpf_lsm.h @@ -19,8 +19,11 @@ extern struct security_hook_heads bpf_lsm_hook_heads; int bpf_lsm_srcu_read_lock(void); void bpf_lsm_srcu_read_unlock(int idx); +int bpf_lsm_verify_prog(const struct bpf_prog *prog); const struct btf_type *bpf_lsm_type_by_idx(struct btf *btf, u32 offset); const struct btf_member *bpf_lsm_head_by_idx(struct btf *btf, u32 idx); +int bpf_lsm_attach(struct bpf_prog *prog); +int bpf_lsm_detach(struct bpf_prog *prog); #define CALL_BPF_LSM_VOID_HOOKS(FUNC, ...) \ do { \ @@ -68,6 +71,10 @@ static inline int bpf_lsm_srcu_read_lock(void) return 0; } static inline void bpf_lsm_srcu_read_unlock(int idx) {} +static inline int bpf_lsm_verify_prog(const struct bpf_prog *prog) +{ + return -EOPNOTSUPP; +} static inline const struct btf_type *bpf_lsm_type_by_idx( struct btf *btf, u32 idx) { @@ -78,6 +85,14 @@ static inline const struct btf_member *bpf_lsm_head_by_idx( { return ERR_PTR(-EOPNOTSUPP); } +static inline int bpf_lsm_attach(struct bpf_prog *prog) +{ + return -EOPNOTSUPP; +} +static inline int bpf_lsm_detach(struct bpf_prog *prog) +{ + return -EOPNOTSUPP; +} #endif /* CONFIG_SECURITY_BPF */ diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 2f1e24a8c4a4..a3206de23db9 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -470,6 +470,10 @@ union bpf_attr { __u32 line_info_cnt; /* number of bpf_line_info records */ __u32 attach_btf_id; /* in-kernel BTF type id to attach to */ __u32 attach_prog_fd; /* 0 to attach to vmlinux */ + /* Index of the hlist_head in security_hook_heads to which the + * program must be attached. + */ + __u32 lsm_hook_idx; }; struct { /* anonymous struct used by BPF_OBJ_* commands */ diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index eab4a36ee889..851ca97120ac 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -4,6 +4,7 @@ #include #include #include +#include #include #include #include @@ -1993,7 +1994,7 @@ bpf_prog_load_check_attach(enum bpf_prog_type prog_type, } /* last field in 'union bpf_attr' used by this command */ -#define BPF_PROG_LOAD_LAST_FIELD attach_prog_fd +#define BPF_PROG_LOAD_LAST_FIELD lsm_hook_idx static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr) { @@ -2047,6 +2048,10 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr) prog->expected_attach_type = attr->expected_attach_type; prog->aux->attach_btf_id = attr->attach_btf_id; + + if (type == BPF_PROG_TYPE_LSM) + prog->aux->lsm_hook_idx = attr->lsm_hook_idx; + if (attr->attach_prog_fd) { struct bpf_prog *tgt_prog; @@ -2213,6 +2218,44 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog) return err; } +static int bpf_lsm_prog_release(struct inode *inode, struct file *filp) +{ + struct bpf_prog *prog = filp->private_data; + + WARN_ON_ONCE(bpf_lsm_detach(prog)); + bpf_prog_put(prog); + return 0; +} + +static const struct file_operations bpf_lsm_prog_fops = { + .release = bpf_lsm_prog_release, + .read = bpf_dummy_read, + .write = bpf_dummy_write, +}; + +static int bpf_lsm_prog_attach(struct bpf_prog *prog) +{ + int ret; + + if (prog->expected_attach_type != BPF_LSM_MAC) + return -EINVAL; + + /* The attach increments the references to the program which is + * decremented on detach as a part of bpf_lsm_hook_free. + */ + ret = bpf_lsm_attach(prog); + if (ret) + return ret; + + ret = anon_inode_getfd("bpf-lsm-prog", &bpf_lsm_prog_fops, + prog, O_CLOEXEC); + if (ret < 0) { + bpf_lsm_detach(prog); + return ret; + } + return 0; +} + struct bpf_raw_tracepoint { struct bpf_raw_event_map *btp; struct bpf_prog *prog; @@ -2431,7 +2474,7 @@ static int bpf_prog_attach(const union bpf_attr *attr) ret = lirc_prog_attach(attr, prog); break; case BPF_PROG_TYPE_LSM: - ret = -EOPNOTSUPP; + ret = bpf_lsm_prog_attach(prog); break; case BPF_PROG_TYPE_FLOW_DISSECTOR: ret = skb_flow_dissector_bpf_prog_attach(attr, prog); diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1cc945daa9c8..1a4013c68afa 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -19,6 +19,7 @@ #include #include #include +#include #include "disasm.h" @@ -6405,8 +6406,9 @@ static int check_return_code(struct bpf_verifier_env *env) struct tnum range = tnum_range(0, 1); int err; - /* The struct_ops func-ptr's return type could be "void" */ - if (env->prog->type == BPF_PROG_TYPE_STRUCT_OPS && + /* LSM and struct_ops func-ptr's return type could be "void" */ + if ((env->prog->type == BPF_PROG_TYPE_STRUCT_OPS || + env->prog->type == BPF_PROG_TYPE_LSM) && !prog->aux->attach_func_proto->type) return 0; @@ -9775,7 +9777,49 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env) return 0; } -static int check_attach_btf_id(struct bpf_verifier_env *env) +/* BPF_PROG_TYPE_LSM programs pass the member index of the LSM hook in the + * security_hook_heads as the lsm_hook_idx. The verifier determines the + * name and the prototype for the LSM hook using the information in + * security_list_options and validates if the offset is a valid hlist_head. + */ +static inline int check_attach_btf_id_lsm(struct bpf_verifier_env *env) +{ + struct bpf_prog *prog = env->prog; + u32 idx = prog->aux->lsm_hook_idx; + const struct btf_member *head; + const struct btf_type *t; + const char *tname; + int ret; + + ret = bpf_lsm_verify_prog(prog); + if (ret < 0) + return -EINVAL; + + t = bpf_lsm_type_by_idx(btf_vmlinux, idx); + if (IS_ERR(t)) { + verbose(env, "unable to find security_list_option for idx %u in security_hook_heads\n", idx); + return -EINVAL; + } + + if (!btf_type_is_func_proto(t)) + return -EINVAL; + + head = bpf_lsm_head_by_idx(btf_vmlinux, idx); + if (IS_ERR(head)) { + verbose(env, "no security_hook_heads index = %u\n", idx); + return PTR_ERR(head); + } + + tname = btf_name_by_offset(btf_vmlinux, head->name_off); + if (!tname || !tname[0]) + return -EINVAL; + + prog->aux->attach_func_name = tname; + prog->aux->attach_func_proto = t; + return 0; +} + +static int check_attach_btf_id_tracing(struct bpf_verifier_env *env) { struct bpf_prog *prog = env->prog; bool prog_extension = prog->type == BPF_PROG_TYPE_EXT; @@ -9791,12 +9835,6 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) long addr; u64 key; - if (prog->type == BPF_PROG_TYPE_STRUCT_OPS) - return check_struct_ops_btf_id(env); - - if (prog->type != BPF_PROG_TYPE_TRACING && !prog_extension) - return 0; - if (!btf_id) { verbose(env, "Tracing programs must provide btf_id\n"); return -EINVAL; @@ -9981,6 +10019,23 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) } } +static int check_attach_btf_id(struct bpf_verifier_env *env) +{ + struct bpf_prog *prog = env->prog; + + switch (prog->type) { + case BPF_PROG_TYPE_TRACING: + case BPF_PROG_TYPE_EXT: + return check_attach_btf_id_tracing(env); + case BPF_PROG_TYPE_STRUCT_OPS: + return check_struct_ops_btf_id(env); + case BPF_PROG_TYPE_LSM: + return check_attach_btf_id_lsm(env); + default: + return 0; + } +} + int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, union bpf_attr __user *uattr) { diff --git a/security/bpf/Kconfig b/security/bpf/Kconfig index 9438d899b618..a915c549f4b8 100644 --- a/security/bpf/Kconfig +++ b/security/bpf/Kconfig @@ -8,6 +8,7 @@ config SECURITY_BPF depends on BPF_SYSCALL depends on SRCU depends on DEBUG_INFO_BTF + depends on BPF_JIT && HAVE_EBPF_JIT help This enables instrumentation of the security hooks with eBPF programs. diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c index e9dc6933b6fa..f1d4fdcdb20e 100644 --- a/security/bpf/hooks.c +++ b/security/bpf/hooks.c @@ -6,11 +6,14 @@ #include #include +#include #include #include #include "bpf_lsm.h" +#define SECURITY_LIST_HEAD(off) ((void *)&bpf_lsm_hook_heads + off) + DEFINE_STATIC_SRCU(security_hook_srcu); int bpf_lsm_srcu_read_lock(void) @@ -41,6 +44,27 @@ static inline int validate_hlist_head(struct btf *btf, return 0; } +int bpf_lsm_verify_prog(const struct bpf_prog *prog) +{ + u32 num_hooks = btf_type_vlen(bpf_lsm_info.btf_hook_heads); + u32 idx = prog->aux->lsm_hook_idx; + struct bpf_verifier_log log = {}; + + if (!prog->gpl_compatible) { + bpf_log(&log, + "LSM programs must have a GPL compatible license\n"); + return -EINVAL; + } + + if (idx >= num_hooks) { + bpf_log(&log, "lsm_hook_idx should be between 0 and %u\n", + num_hooks - 1); + return -EINVAL; + } + + return 0; +} + /* Find the BTF representation of the security_hook_heads member for a member * with a given index in struct security_hook_heads. */ @@ -93,3 +117,180 @@ const struct btf_type *bpf_lsm_type_by_idx(struct btf *btf, u32 idx) return ERR_PTR(-ESRCH); } + +static void *bpf_lsm_get_func_addr(struct security_hook_list *s, + const char *name) +{ + const struct btf_member *member; + s32 i; + + for_each_member(i, bpf_lsm_info.btf_hook_types, member) + if (!strncmp(btf_name_by_offset(btf_vmlinux, member->name_off), + name, strlen(name) + 1)) + return (void *)&s->hook + member->offset / 8; + + return ERR_PTR(-ESRCH); +} + +static struct bpf_lsm_list *bpf_lsm_list_lookup(struct bpf_prog *prog) +{ + struct bpf_verifier_log bpf_log = {}; + u32 idx = prog->aux->lsm_hook_idx; + const struct btf_member *head; + struct bpf_lsm_list *list; + int ret = 0; + + list = &bpf_lsm_info.hook_lists[idx]; + + mutex_lock(&list->mutex); + + if (list->initialized) + goto unlock; + + list->attach_type = prog->aux->attach_func_proto; + + ret = btf_distill_func_proto(&bpf_log, btf_vmlinux, list->attach_type, + prog->aux->attach_func_name, + &list->func_model); + if (ret) + goto unlock; + + head = bpf_lsm_head_by_idx(btf_vmlinux, idx); + if (IS_ERR(head)) { + ret = PTR_ERR(head); + goto unlock; + } + + list->security_list_head = SECURITY_LIST_HEAD(head->offset / 8); + list->initialized = true; +unlock: + mutex_unlock(&list->mutex); + if (ret) + return ERR_PTR(ret); + return list; +} + +static struct bpf_lsm_hook *bpf_lsm_hook_alloc(struct bpf_lsm_list *list, + struct bpf_prog *prog) +{ + struct bpf_lsm_hook *hook; + void *image; + int ret = 0; + + image = bpf_jit_alloc_exec(PAGE_SIZE); + if (!image) + return ERR_PTR(-ENOMEM); + + set_vm_flush_reset_perms(image); + + ret = arch_prepare_bpf_trampoline(image, image + PAGE_SIZE, + &list->func_model, 0, &prog, 1, NULL, 0, NULL); + if (ret < 0) { + ret = -EINVAL; + goto error; + } + + hook = kzalloc(sizeof(struct bpf_lsm_hook), GFP_KERNEL); + if (!hook) { + ret = -ENOMEM; + goto error; + } + + hook->image = image; + hook->prog = prog; + bpf_prog_inc(prog); + return hook; +error: + bpf_jit_free_exec(image); + return ERR_PTR(ret); +} + +static void bpf_lsm_hook_free(struct bpf_lsm_hook *tr) +{ + if (!tr) + return; + + if (tr->prog) + bpf_prog_put(tr->prog); + + bpf_jit_free_exec(tr->image); + kfree(tr); +} + +int bpf_lsm_attach(struct bpf_prog *prog) +{ + struct bpf_lsm_hook *hook; + struct bpf_lsm_list *list; + void **addr; + int ret = 0; + + /* Only CAP_MAC_ADMIN users are allowed to make changes to LSM hooks + */ + if (!capable(CAP_MAC_ADMIN)) + return -EPERM; + + if (!bpf_lsm_info.initialized) + return -EBUSY; + + list = bpf_lsm_list_lookup(prog); + if (IS_ERR(list)) + return PTR_ERR(list); + + hook = bpf_lsm_hook_alloc(list, prog); + if (IS_ERR(hook)) + return PTR_ERR(hook); + + hook->sec_hook.head = list->security_list_head; + addr = bpf_lsm_get_func_addr(&hook->sec_hook, + prog->aux->attach_func_name); + if (IS_ERR(addr)) { + ret = PTR_ERR(addr); + goto error; + } + + *addr = hook->image; + + mutex_lock(&list->mutex); + hlist_add_tail_rcu(&hook->sec_hook.list, hook->sec_hook.head); + mutex_unlock(&list->mutex); + return 0; + +error: + bpf_lsm_hook_free(hook); + return ret; +} + +int bpf_lsm_detach(struct bpf_prog *prog) +{ + struct security_hook_list *sec_hook; + struct bpf_lsm_hook *hook = NULL; + struct bpf_lsm_list *list; + struct hlist_node *n; + + /* Only CAP_MAC_ADMIN users are allowed to make changes to LSM hooks + */ + if (!capable(CAP_MAC_ADMIN)) + return -EPERM; + + if (!bpf_lsm_info.initialized) + return -EBUSY; + + list = &bpf_lsm_info.hook_lists[prog->aux->lsm_hook_idx]; + + mutex_lock(&list->mutex); + hlist_for_each_entry_safe(sec_hook, n, list->security_list_head, list) { + hook = container_of(sec_hook, struct bpf_lsm_hook, sec_hook); + if (hook->prog == prog) { + hlist_del_rcu(&hook->sec_hook.list); + break; + } + } + mutex_unlock(&list->mutex); + /* call_rcu is not used directly as module_memfree cannot run from an + * softirq context. The best way would be to schedule this on a work + * queue. + */ + synchronize_srcu(&security_hook_srcu); + bpf_lsm_hook_free(hook); + return 0; +} diff --git a/security/bpf/include/bpf_lsm.h b/security/bpf/include/bpf_lsm.h index f142596d97bd..4c51ce4d29e7 100644 --- a/security/bpf/include/bpf_lsm.h +++ b/security/bpf/include/bpf_lsm.h @@ -4,9 +4,50 @@ #define _BPF_LSM_H #include +#include #include #include +struct bpf_lsm_hook { + /* The security_hook_list is initialized dynamically. These are + * initialized in static LSMs by LSM_HOOK_INIT. + */ + struct security_hook_list sec_hook; + /* The BPF program for which this hook was allocated, this is used upon + * detachment to find the hook corresponding to a program. + */ + struct bpf_prog *prog; + /* The address of the allocated function */ + void *image; +}; + +/* The list represents the list of hooks attached to a particular + * security_list_head and contains information required for attaching and + * detaching BPF Programs. + */ +struct bpf_lsm_list { + /* Used on the first attached BPF program to populate the remaining + * information + */ + bool initialized; + /* This mutex is used to serialize accesses to all the fields in + * this structure. + */ + struct mutex mutex; + /* The BTF type for this hook. + */ + const struct btf_type *attach_type; + /* func_model for the setup of the callback. + */ + struct btf_func_model func_model; + /* The list of functions currently associated with the LSM hook. + */ + struct list_head callback_list; + /* The head to which the allocated hooks must be attached to. + */ + struct hlist_head *security_list_head; +}; + struct bpf_lsm_info { /* BTF type for security_hook_heads populated at init. */ @@ -14,6 +55,14 @@ struct bpf_lsm_info { /* BTF type for security_list_options populated at init. */ const struct btf_type *btf_hook_types; + /* Dynamic Hooks can only be attached after the LSM is initialized. + */ + bool initialized; + /* The hook_lists is allocated during __init and mutexes for each + * bpf_lsm_list are initialized on __init, the remaining initialization + * happens when a BPF program is attached to the list. + */ + struct bpf_lsm_list *hook_lists; }; extern struct bpf_lsm_info bpf_lsm_info; diff --git a/security/bpf/lsm.c b/security/bpf/lsm.c index 736e0ee3f926..8555879af8c8 100644 --- a/security/bpf/lsm.c +++ b/security/bpf/lsm.c @@ -26,6 +26,8 @@ struct bpf_lsm_info bpf_lsm_info; static __init int bpf_lsm_info_init(void) { const struct btf_type *t; + u32 num_hooks; + int i; if (!btf_vmlinux) /* No need to grab any locks because we are still in init */ @@ -42,6 +44,7 @@ static __init int bpf_lsm_info_init(void) return PTR_ERR(t); bpf_lsm_info.btf_hook_heads = t; + num_hooks = btf_type_vlen(t); t = btf_type_by_name_kind(btf_vmlinux, "security_list_options", BTF_KIND_UNION); @@ -49,6 +52,22 @@ static __init int bpf_lsm_info_init(void) return PTR_ERR(t); bpf_lsm_info.btf_hook_types = t; + + bpf_lsm_info.hook_lists = kcalloc(num_hooks, + sizeof(struct bpf_lsm_list), + GFP_KERNEL); + if (!bpf_lsm_info.hook_lists) + return -ENOMEM; + + /* The mutex needs to be initialized at init as it must be held + * when mutating the list. The rest of the information in the list + * is populated lazily when the first LSM hook callback is appeneded + * to the list. + */ + for (i = 0; i < num_hooks; i++) + mutex_init(&bpf_lsm_info.hook_lists[i].mutex); + + bpf_lsm_info.initialized = true; return 0; } diff --git a/security/bpf/ops.c b/security/bpf/ops.c index 81c2bd9c0495..9a26633ac6f3 100644 --- a/security/bpf/ops.c +++ b/security/bpf/ops.c @@ -6,6 +6,7 @@ #include #include +#include const struct bpf_prog_ops lsm_prog_ops = { }; @@ -25,4 +26,5 @@ static const struct bpf_func_proto *get_bpf_func_proto( const struct bpf_verifier_ops lsm_verifier_ops = { .get_func_proto = get_bpf_func_proto, + .is_valid_access = btf_ctx_access, }; diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 2f1e24a8c4a4..a3206de23db9 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -470,6 +470,10 @@ union bpf_attr { __u32 line_info_cnt; /* number of bpf_line_info records */ __u32 attach_btf_id; /* in-kernel BTF type id to attach to */ __u32 attach_prog_fd; /* 0 to attach to vmlinux */ + /* Index of the hlist_head in security_hook_heads to which the + * program must be attached. + */ + __u32 lsm_hook_idx; }; struct { /* anonymous struct used by BPF_OBJ_* commands */ -- 2.20.1