nfp: bpf: protect against mis-initializing atomic counters

Atomic operations on the NFP are currently always in big endian.
The driver keeps track of regions of memory storing atomic values
and byte swaps them accordingly.  There are corner cases where
the map values may be initialized before the driver knows they
are used as atomic counters.  This can happen either when the
datapath is performing the update and the stack contents are
unknown or when map is updated before the program which will
use it for atomic values is loaded.

To avoid situation where user initializes the value to 0 1 2 3
and then after loading a program which uses the word as an atomic
counter starts reading 3 2 1 0 - only allow atomic counters to be
initialized to endian-neutral values.

For updates from the datapath the stack information may not be
as precise, so just allow initializing such values to 0.

Example code which would break:
struct bpf_map_def SEC("maps") rxcnt = {
       .type = BPF_MAP_TYPE_HASH,
       .key_size = sizeof(__u32),
       .value_size = sizeof(__u64),
       .max_entries = 1,
};

int xdp_prog1()
{
      	__u64 nonzeroval = 3;
	__u32 key = 0;
	__u64 *value;

	value = bpf_map_lookup_elem(&rxcnt, &key);
	if (!value)
		bpf_map_update_elem(&rxcnt, &key, &nonzeroval, BPF_ANY);
	else
		__sync_fetch_and_add(value, 1);

	return XDP_PASS;
}

$ offload bpftool map dump
key: 00 00 00 00 value: 00 00 00 03 00 00 00 00

should be:

$ offload bpftool map dump
key: 00 00 00 00 value: 03 00 00 00 00 00 00 00

Reported-by: David Beckett <david.beckett@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/drivers/net/ethernet/netronome/nfp/bpf/offload.c b/drivers/net/ethernet/netronome/nfp/bpf/offload.c
index 927e038d9f77..658c7143d59c 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/offload.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/offload.c
@@ -262,10 +262,25 @@ static void nfp_map_bpf_byte_swap(struct nfp_bpf_map *nfp_map, void *value)
 	unsigned int i;
 
 	for (i = 0; i < DIV_ROUND_UP(nfp_map->offmap->map.value_size, 4); i++)
-		if (nfp_map->use_map[i] == NFP_MAP_USE_ATOMIC_CNT)
+		if (nfp_map->use_map[i].type == NFP_MAP_USE_ATOMIC_CNT)
 			word[i] = (__force u32)cpu_to_be32(word[i]);
 }
 
+/* Mark value as unsafely initialized in case it becomes atomic later
+ * and we didn't byte swap something non-byte swap neutral.
+ */
+static void
+nfp_map_bpf_byte_swap_record(struct nfp_bpf_map *nfp_map, void *value)
+{
+	u32 *word = value;
+	unsigned int i;
+
+	for (i = 0; i < DIV_ROUND_UP(nfp_map->offmap->map.value_size, 4); i++)
+		if (nfp_map->use_map[i].type == NFP_MAP_UNUSED &&
+		    word[i] != (__force u32)cpu_to_be32(word[i]))
+			nfp_map->use_map[i].non_zero_update = 1;
+}
+
 static int
 nfp_bpf_map_lookup_entry(struct bpf_offloaded_map *offmap,
 			 void *key, void *value)
@@ -285,6 +300,7 @@ nfp_bpf_map_update_entry(struct bpf_offloaded_map *offmap,
 			 void *key, void *value, u64 flags)
 {
 	nfp_map_bpf_byte_swap(offmap->dev_priv, value);
+	nfp_map_bpf_byte_swap_record(offmap->dev_priv, value);
 	return nfp_bpf_ctrl_update_entry(offmap, key, value, flags);
 }