selftests/bpf: Add write to hashmap to array_map iter test

Modify iter prog in existing bpf_iter_bpf_array_map.c, which currently
dumps arraymap key/val, to also do a write of (val, key) into a
newly-added hashmap. Confirm that the write succeeds as expected by
modifying the userspace runner program.

Before a change added in an earlier commit - considering PTR_TO_BUF reg
a valid input to helpers which expect MAP_{KEY,VAL} - the verifier
would've rejected this prog change due to type mismatch. Since using
current iter's key/val to access a separate map is a reasonable usecase,
let's add support for it.

Note that the test prog cannot directly write (val, key) into hashmap
via bpf_map_update_elem when both come from iter context because key is
marked MEM_RDONLY. This is due to bpf_map_update_elem - and other basic
map helpers - taking ARG_PTR_TO_MAP_{KEY,VALUE} w/o MEM_RDONLY type
flag. bpf_map_{lookup,update,delete}_elem don't modify their
input key/val so it should be possible to tag their args READONLY, but
due to the ubiquitous use of these helpers and verifier checks for
type == MAP_VALUE, such a change is nontrivial and seems better to
address in a followup series.

Also fixup some 'goto's in test runner's map checking loop.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221020160721.4030492-4-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 20 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_array_map.c b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_array_map.c
index 6286023fd62b..c5969ca6f26b 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_array_map.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_array_map.c
@@ -19,13 +19,20 @@ struct {
 	__type(value, __u64);
 } arraymap1 SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 10);
+	__type(key, __u64);
+	__type(value, __u32);
+} hashmap1 SEC(".maps");
+
 __u32 key_sum = 0;
 __u64 val_sum = 0;
 
 SEC("iter/bpf_map_elem")
 int dump_bpf_array_map(struct bpf_iter__bpf_map_elem *ctx)
 {
-	__u32 *key = ctx->key;
+	__u32 *hmap_val, *key = ctx->key;
 	__u64 *val = ctx->value;
 
 	if (key == (void *)0 || val == (void *)0)
@@ -35,6 +42,18 @@ int dump_bpf_array_map(struct bpf_iter__bpf_map_elem *ctx)
 	bpf_seq_write(ctx->meta->seq, val, sizeof(__u64));
 	key_sum += *key;
 	val_sum += *val;
+
+	/* workaround - It's necessary to do this convoluted (val, key)
+	 * write into hashmap1, instead of simply doing
+	 *   bpf_map_update_elem(&hashmap1, val, key, BPF_ANY);
+	 * because key has MEM_RDONLY flag and bpf_map_update elem expects
+	 * types without this flag
+	 */
+	bpf_map_update_elem(&hashmap1, val, val, BPF_ANY);
+	hmap_val = bpf_map_lookup_elem(&hashmap1, val);
+	if (hmap_val)
+		*hmap_val = *key;
+
 	*val = *key;
 	return 0;
 }