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>

1 files changed, 5 insertions, 1 deletions

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 1a6e9861d554..217b10bd9f48 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -22,7 +22,7 @@
 #include "map_in_map.h"
 
 #define ARRAY_CREATE_FLAG_MASK \
-        (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
+        (BPF_F_NUMA_NODE | BPF_F_ACCESS_MASK)
 
 static void bpf_array_free_percpu(struct bpf_array *array)
 {
@@ -63,6 +63,7 @@ int array_map_alloc_check(union bpf_attr *attr)
         if (attr->max_entries == 0 || attr->key_size != 4 ||
             attr->value_size == 0 ||
             attr->map_flags & ~ARRAY_CREATE_FLAG_MASK ||
+            !bpf_map_flags_access_ok(attr->map_flags) ||
             (percpu && numa_node != NUMA_NO_NODE))
                 return -EINVAL;
 
@@ -472,6 +473,9 @@ static int fd_array_map_alloc_check(union bpf_attr *attr)
         /* only file descriptors can be stored in this type of map */
         if (attr->value_size != sizeof(u32))
                 return -EINVAL;
+        /* Program read-only/write-only not supported for special maps yet. */
+        if (attr->map_flags & (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG))
+                return -EINVAL;
         return array_map_alloc_check(attr);
 }