bpf: add program side {rd, wr}only support for maps

This work adds two new map creation flags BPF_F_RDONLY_PROG
and BPF_F_WRONLY_PROG in order to allow for read-only or
write-only BPF maps from a BPF program side.

Today we have BPF_F_RDONLY and BPF_F_WRONLY, but this only
applies to system call side, meaning the BPF program has full
read/write access to the map as usual while bpf(2) calls with
map fd can either only read or write into the map depending
on the flags. BPF_F_RDONLY_PROG and BPF_F_WRONLY_PROG allows
for the exact opposite such that verifier is going to reject
program loads if write into a read-only map or a read into a
write-only map is detected. For read-only map case also some
helpers are forbidden for programs that would alter the map
state such as map deletion, update, etc. As opposed to the two
BPF_F_RDONLY / BPF_F_WRONLY flags, BPF_F_RDONLY_PROG as well
as BPF_F_WRONLY_PROG really do correspond to the map lifetime.

We've enabled this generic map extension to various non-special
maps holding normal user data: array, hash, lru, lpm, local
storage, queue and stack. Further generic map types could be
followed up in future depending on use-case. Main use case
here is to forbid writes into .rodata map values from verifier
side.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/local_storage.c

@@ -14,7 +14,7 @@ DEFINE_PER_CPU(struct bpf_cgroup_storage*, bpf_cgroup_storage[MAX_BPF_CGROUP_STO
 #ifdef CONFIG_CGROUP_BPF
 
 #define LOCAL_STORAGE_CREATE_FLAG_MASK					\
-	(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
+	(BPF_F_NUMA_NODE | BPF_F_ACCESS_MASK)
 
 struct bpf_cgroup_storage_map {
 	struct bpf_map map;
@@ -282,8 +282,8 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 	if (attr->value_size > PAGE_SIZE)
 		return ERR_PTR(-E2BIG);
 
-	if (attr->map_flags & ~LOCAL_STORAGE_CREATE_FLAG_MASK)
-		/* reserved bits should not be used */
+	if (attr->map_flags & ~LOCAL_STORAGE_CREATE_FLAG_MASK ||
+	    !bpf_map_flags_access_ok(attr->map_flags))
 		return ERR_PTR(-EINVAL);
 
 	if (attr->max_entries)