bpf: Adapt copy_map_value for multiple offset case

Since now there might be at most 10 offsets that need handling in
copy_map_value, the manual shuffling and special case is no longer going
to work. Hence, let's generalise the copy_map_value function by using
a sorted array of offsets to skip regions that must be avoided while
copying into and out of a map value.

When the map is created, we populate the offset array in struct map,
Then, copy_map_value uses this sorted offset array is used to memcpy
while skipping timer, spin lock, and kptr. The array is allocated as
in most cases none of these special fields would be present in map
value, hence we can save on space for the common case by not embedding
the entire object inside bpf_map struct.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220424214901.2743946-6-memxor@gmail.com

1 files changed, 87 insertions, 1 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 575b09339360..4d419a3effc4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -30,6 +30,7 @@
 #include <linux/pgtable.h>
 #include <linux/bpf_lsm.h>
 #include <linux/poll.h>
+#include <linux/sort.h>
 #include <linux/bpf-netns.h>
 #include <linux/rcupdate_trace.h>
 #include <linux/memcontrol.h>
@@ -551,6 +552,7 @@ static void bpf_map_free_deferred(struct work_struct *work)
 	struct bpf_map *map = container_of(work, struct bpf_map, work);
 
 	security_bpf_map_free(map);
+	kfree(map->off_arr);
 	bpf_map_free_kptr_off_tab(map);
 	bpf_map_release_memcg(map);
 	/* implementation dependent freeing */
@@ -840,6 +842,84 @@ int map_check_no_btf(const struct bpf_map *map,
 	return -ENOTSUPP;
 }
 
+static int map_off_arr_cmp(const void *_a, const void *_b, const void *priv)
+{
+	const u32 a = *(const u32 *)_a;
+	const u32 b = *(const u32 *)_b;
+
+	if (a < b)
+		return -1;
+	else if (a > b)
+		return 1;
+	return 0;
+}
+
+static void map_off_arr_swap(void *_a, void *_b, int size, const void *priv)
+{
+	struct bpf_map *map = (struct bpf_map *)priv;
+	u32 *off_base = map->off_arr->field_off;
+	u32 *a = _a, *b = _b;
+	u8 *sz_a, *sz_b;
+
+	sz_a = map->off_arr->field_sz + (a - off_base);
+	sz_b = map->off_arr->field_sz + (b - off_base);
+
+	swap(*a, *b);
+	swap(*sz_a, *sz_b);
+}
+
+static int bpf_map_alloc_off_arr(struct bpf_map *map)
+{
+	bool has_spin_lock = map_value_has_spin_lock(map);
+	bool has_timer = map_value_has_timer(map);
+	bool has_kptrs = map_value_has_kptrs(map);
+	struct bpf_map_off_arr *off_arr;
+	u32 i;
+
+	if (!has_spin_lock && !has_timer && !has_kptrs) {
+		map->off_arr = NULL;
+		return 0;
+	}
+
+	off_arr = kmalloc(sizeof(*map->off_arr), GFP_KERNEL | __GFP_NOWARN);
+	if (!off_arr)
+		return -ENOMEM;
+	map->off_arr = off_arr;
+
+	off_arr->cnt = 0;
+	if (has_spin_lock) {
+		i = off_arr->cnt;
+
+		off_arr->field_off[i] = map->spin_lock_off;
+		off_arr->field_sz[i] = sizeof(struct bpf_spin_lock);
+		off_arr->cnt++;
+	}
+	if (has_timer) {
+		i = off_arr->cnt;
+
+		off_arr->field_off[i] = map->timer_off;
+		off_arr->field_sz[i] = sizeof(struct bpf_timer);
+		off_arr->cnt++;
+	}
+	if (has_kptrs) {
+		struct bpf_map_value_off *tab = map->kptr_off_tab;
+		u32 *off = &off_arr->field_off[off_arr->cnt];
+		u8 *sz = &off_arr->field_sz[off_arr->cnt];
+
+		for (i = 0; i < tab->nr_off; i++) {
+			*off++ = tab->off[i].offset;
+			*sz++ = sizeof(u64);
+		}
+		off_arr->cnt += tab->nr_off;
+	}
+
+	if (off_arr->cnt == 1)
+		return 0;
+	sort_r(off_arr->field_off, off_arr->cnt, sizeof(off_arr->field_off[0]),
+	       map_off_arr_cmp, map_off_arr_swap, map);
+	return 0;
+}
+
 static int map_check_btf(struct bpf_map *map, const struct btf *btf,
 			 u32 btf_key_id, u32 btf_value_id)
 {
@@ -1009,10 +1089,14 @@ static int map_create(union bpf_attr *attr)
 			attr->btf_vmlinux_value_type_id;
 	}
 
-	err = security_bpf_map_alloc(map);
+	err = bpf_map_alloc_off_arr(map);
 	if (err)
 		goto free_map;
 
+	err = security_bpf_map_alloc(map);
+	if (err)
+		goto free_map_off_arr;
+
 	err = bpf_map_alloc_id(map);
 	if (err)
 		goto free_map_sec;
@@ -1035,6 +1119,8 @@ static int map_create(union bpf_attr *attr)
 
 free_map_sec:
 	security_bpf_map_free(map);
+free_map_off_arr:
+	kfree(map->off_arr);
 free_map:
 	btf_put(map->btf);
 	map->ops->map_free(map);