[PATCH bpf-next 5/7] bpf: add function to load builtin BPF program

["Björn Töpel" <bjorn.topel@gmail.com>]

From: Björn Töpel <bjorn.topel@intel.com>

The added bpf_prog_load_builtin can be used to load and verify a BPF
program that originates from the kernel. We call this a "builtin BPF
program". A builtin program can be used for convenience, e.g. it
allows for the kernel to use the bpf infrastructure for internal
tasks.

This functionality will be used by AF_XDP sockets in a later commit.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
 include/linux/bpf.h  |  2 ++
 kernel/bpf/syscall.c | 32 ++++++++++++++++++++++++--------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e82b7039fc66..e810bfeb6239 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -563,6 +563,8 @@ static inline int bpf_map_attr_numa_node(const union bpf_attr *attr)
 struct bpf_prog *bpf_prog_get_type_path(const char *name, enum bpf_prog_type type);
 int array_map_alloc_check(union bpf_attr *attr);
 
+struct bpf_prog *bpf_prog_load_builtin(union bpf_attr *attr);
+
 #else /* !CONFIG_BPF_SYSCALL */
 static inline struct bpf_prog *bpf_prog_get(u32 ufd)
 {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index ee1328625330..323831e1a1e2 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1461,10 +1461,16 @@ static struct bpf_prog *__bpf_prog_load(union bpf_attr *attr,
 	    !capable(CAP_SYS_ADMIN))
 		return ERR_PTR(-EPERM);
 
-	/* copy eBPF program license from user space */
-	if (strncpy_from_user(license, u64_to_user_ptr(attr->license),
-			      sizeof(license) - 1) < 0)
-		return ERR_PTR(-EFAULT);
+	/* NB! If uattr is NULL, a builtin BPF is being loaded. */
+	if (uattr) {
+		/* copy eBPF program license from user space */
+		if (strncpy_from_user(license, u64_to_user_ptr(attr->license),
+				      sizeof(license) - 1) < 0)
+			return ERR_PTR(-EFAULT);
+	} else {
+		strncpy(license, (const char *)(unsigned long)attr->license,
+			sizeof(license) - 1);
+	}
 	license[sizeof(license) - 1] = 0;
 
 	/* eBPF programs must be GPL compatible to use GPL-ed functions */
@@ -1505,10 +1511,15 @@ static struct bpf_prog *__bpf_prog_load(union bpf_attr *attr,
 
 	prog->len = attr->insn_cnt;
 
-	err = -EFAULT;
-	if (copy_from_user(prog->insns, u64_to_user_ptr(attr->insns),
-			   bpf_prog_insn_size(prog)) != 0)
-		goto free_prog;
+	if (uattr) {
+		err = -EFAULT;
+		if (copy_from_user(prog->insns, u64_to_user_ptr(attr->insns),
+				   bpf_prog_insn_size(prog)) != 0)
+			goto free_prog;
+	} else {
+		memcpy(prog->insns, (void *)(unsigned long)attr->insns,
+		       bpf_prog_insn_size(prog));
+	}
 
 	prog->orig_prog = NULL;
 	prog->jited = 0;
@@ -1584,6 +1595,11 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
 	return fd;
 }
 
+struct bpf_prog *bpf_prog_load_builtin(union bpf_attr *attr)
+{
+	return __bpf_prog_load(attr, NULL);
+}
+
 #define BPF_OBJ_LAST_FIELD file_flags
 
 static int bpf_obj_pin(const union bpf_attr *attr)
-- 
2.19.1