bpf: expand BPF syscall with program load/unload

eBPF programs are similar to kernel modules. They are loaded by the user
process and automatically unloaded when process exits. Each eBPF program is
a safe run-to-completion set of instructions. eBPF verifier statically
determines that the program terminates and is safe to execute.

The following syscall wrapper can be used to load the program:
int bpf_prog_load(enum bpf_prog_type prog_type,
                  const struct bpf_insn *insns, int insn_cnt,
                  const char *license)
{
    union bpf_attr attr = {
        .prog_type = prog_type,
        .insns = ptr_to_u64(insns),
        .insn_cnt = insn_cnt,
        .license = ptr_to_u64(license),
    };

    return bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
}
where 'insns' is an array of eBPF instructions and 'license' is a string
that must be GPL compatible to call helper functions marked gpl_only

Upon succesful load the syscall returns prog_fd.
Use close(prog_fd) to unload the program.

User space tests and examples follow in the later patches

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 180 insertions, 14 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 8b7002488251..f0c30c59b317 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -27,6 +27,7 @@
 #include <linux/random.h>
 #include <linux/moduleloader.h>
 #include <asm/unaligned.h>
+#include <linux/bpf.h>
 
 /* Registers */
 #define BPF_R0  regs[BPF_REG_0]
@@ -71,7 +72,7 @@ struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags)
 {
         gfp_t gfp_flags = GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO |
                           gfp_extra_flags;
-        struct bpf_work_struct *ws;
+        struct bpf_prog_aux *aux;
         struct bpf_prog *fp;
 
         size = round_up(size, PAGE_SIZE);
@@ -79,14 +80,14 @@ struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags)
         if (fp == NULL)
                 return NULL;
 
-        ws = kmalloc(sizeof(*ws), GFP_KERNEL | gfp_extra_flags);
-        if (ws == NULL) {
+        aux = kzalloc(sizeof(*aux), GFP_KERNEL | gfp_extra_flags);
+        if (aux == NULL) {
                 vfree(fp);
                 return NULL;
         }
 
         fp->pages = size / PAGE_SIZE;
-        fp->work = ws;
+        fp->aux = aux;
 
         return fp;
 }
@@ -110,10 +111,10 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
                 memcpy(fp, fp_old, fp_old->pages * PAGE_SIZE);
                 fp->pages = size / PAGE_SIZE;
 
-                /* We keep fp->work from fp_old around in the new
+                /* We keep fp->aux from fp_old around in the new
                  * reallocated structure.
                  */
-                fp_old->work = NULL;
+                fp_old->aux = NULL;
                 __bpf_prog_free(fp_old);
         }
 
@@ -123,7 +124,7 @@ EXPORT_SYMBOL_GPL(bpf_prog_realloc);
 
 void __bpf_prog_free(struct bpf_prog *fp)
 {
-        kfree(fp->work);
+        kfree(fp->aux);
         vfree(fp);
 }
 EXPORT_SYMBOL_GPL(__bpf_prog_free);
@@ -638,19 +639,19 @@ EXPORT_SYMBOL_GPL(bpf_prog_select_runtime);
 
 static void bpf_prog_free_deferred(struct work_struct *work)
 {
-        struct bpf_work_struct *ws;
+        struct bpf_prog_aux *aux;
 
-        ws = container_of(work, struct bpf_work_struct, work);
-        bpf_jit_free(ws->prog);
+        aux = container_of(work, struct bpf_prog_aux, work);
+        bpf_jit_free(aux->prog);
 }
 
 /* Free internal BPF program */
 void bpf_prog_free(struct bpf_prog *fp)
 {
-        struct bpf_work_struct *ws = fp->work;
+        struct bpf_prog_aux *aux = fp->aux;
 
-        INIT_WORK(&ws->work, bpf_prog_free_deferred);
-        ws->prog = fp;
-        schedule_work(&ws->work);
+        INIT_WORK(&aux->work, bpf_prog_free_deferred);
+        aux->prog = fp;
+        schedule_work(&aux->work);
 }
 EXPORT_SYMBOL_GPL(bpf_prog_free);
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f94349ecaf61..0afb4eaa1887 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -14,6 +14,8 @@
 #include <linux/slab.h>
 #include <linux/anon_inodes.h>
 #include <linux/file.h>
+#include <linux/license.h>
+#include <linux/filter.h>
 
 static LIST_HEAD(bpf_map_types);
 
@@ -334,6 +336,166 @@ err_put:
         return err;
 }
 
+static LIST_HEAD(bpf_prog_types);
+
+static int find_prog_type(enum bpf_prog_type type, struct bpf_prog *prog)
+{
+        struct bpf_prog_type_list *tl;
+
+        list_for_each_entry(tl, &bpf_prog_types, list_node) {
+                if (tl->type == type) {
+                        prog->aux->ops = tl->ops;
+                        prog->aux->prog_type = type;
+                        return 0;
+                }
+        }
+        return -EINVAL;
+}
+
+void bpf_register_prog_type(struct bpf_prog_type_list *tl)
+{
+        list_add(&tl->list_node, &bpf_prog_types);
+}
+
+/* drop refcnt on maps used by eBPF program and free auxilary data */
+static void free_used_maps(struct bpf_prog_aux *aux)
+{
+        int i;
+
+        for (i = 0; i < aux->used_map_cnt; i++)
+                bpf_map_put(aux->used_maps[i]);
+
+        kfree(aux->used_maps);
+}
+
+void bpf_prog_put(struct bpf_prog *prog)
+{
+        if (atomic_dec_and_test(&prog->aux->refcnt)) {
+                free_used_maps(prog->aux);
+                bpf_prog_free(prog);
+        }
+}
+
+static int bpf_prog_release(struct inode *inode, struct file *filp)
+{
+        struct bpf_prog *prog = filp->private_data;
+
+        bpf_prog_put(prog);
+        return 0;
+}
+
+static const struct file_operations bpf_prog_fops = {
+        .release = bpf_prog_release,
+};
+
+static struct bpf_prog *get_prog(struct fd f)
+{
+        struct bpf_prog *prog;
+
+        if (!f.file)
+                return ERR_PTR(-EBADF);
+
+        if (f.file->f_op != &bpf_prog_fops) {
+                fdput(f);
+                return ERR_PTR(-EINVAL);
+        }
+
+        prog = f.file->private_data;
+
+        return prog;
+}
+
+/* called by sockets/tracing/seccomp before attaching program to an event
+ * pairs with bpf_prog_put()
+ */
+struct bpf_prog *bpf_prog_get(u32 ufd)
+{
+        struct fd f = fdget(ufd);
+        struct bpf_prog *prog;
+
+        prog = get_prog(f);
+
+        if (IS_ERR(prog))
+                return prog;
+
+        atomic_inc(&prog->aux->refcnt);
+        fdput(f);
+        return prog;
+}
+
+/* last field in 'union bpf_attr' used by this command */
+#define BPF_PROG_LOAD_LAST_FIELD license
+
+static int bpf_prog_load(union bpf_attr *attr)
+{
+        enum bpf_prog_type type = attr->prog_type;
+        struct bpf_prog *prog;
+        int err;
+        char license[128];
+        bool is_gpl;
+
+        if (CHECK_ATTR(BPF_PROG_LOAD))
+                return -EINVAL;
+
+        /* copy eBPF program license from user space */
+        if (strncpy_from_user(license, u64_to_ptr(attr->license),
+                              sizeof(license) - 1) < 0)
+                return -EFAULT;
+        license[sizeof(license) - 1] = 0;
+
+        /* eBPF programs must be GPL compatible to use GPL-ed functions */
+        is_gpl = license_is_gpl_compatible(license);
+
+        if (attr->insn_cnt >= BPF_MAXINSNS)
+                return -EINVAL;
+
+        /* plain bpf_prog allocation */
+        prog = bpf_prog_alloc(bpf_prog_size(attr->insn_cnt), GFP_USER);
+        if (!prog)
+                return -ENOMEM;
+
+        prog->len = attr->insn_cnt;
+
+        err = -EFAULT;
+        if (copy_from_user(prog->insns, u64_to_ptr(attr->insns),
+                           prog->len * sizeof(struct bpf_insn)) != 0)
+                goto free_prog;
+
+        prog->orig_prog = NULL;
+        prog->jited = false;
+
+        atomic_set(&prog->aux->refcnt, 1);
+        prog->aux->is_gpl_compatible = is_gpl;
+
+        /* find program type: socket_filter vs tracing_filter */
+        err = find_prog_type(type, prog);
+        if (err < 0)
+                goto free_prog;
+
+        /* run eBPF verifier */
+        /* err = bpf_check(prog, tb); */
+
+        if (err < 0)
+                goto free_used_maps;
+
+        /* eBPF program is ready to be JITed */
+        bpf_prog_select_runtime(prog);
+
+        err = anon_inode_getfd("bpf-prog", &bpf_prog_fops, prog, O_RDWR | O_CLOEXEC);
+
+        if (err < 0)
+                /* failed to allocate fd */
+                goto free_used_maps;
+
+        return err;
+
+free_used_maps:
+        free_used_maps(prog->aux);
+free_prog:
+        bpf_prog_free(prog);
+        return err;
+}
+
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
         union bpf_attr attr = {};
@@ -395,6 +557,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
         case BPF_MAP_GET_NEXT_KEY:
                 err = map_get_next_key(&attr);
                 break;
+        case BPF_PROG_LOAD:
+                err = bpf_prog_load(&attr);
+                break;
         default:
                 err = -EINVAL;
                 break;