Patch "libbpf: Convert st_ops->data to shadow type." has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    libbpf: Convert st_ops->data to shadow type.

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     libbpf-convert-st_ops-data-to-shadow-type.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit baf8312a8fc1a0eaec7c8d7bdee15c6c69d0756d
Author: Kui-Feng Lee <thinker.li@xxxxxxxxx>
Date:   Wed Feb 28 22:45:20 2024 -0800

    libbpf: Convert st_ops->data to shadow type.
    
    [ Upstream commit 69e4a9d2b3f5adf5af4feeab0a9f505da971265a ]
    
    Convert st_ops->data to the shadow type of the struct_ops map. The shadow
    type of a struct_ops type is a variant of the original struct type
    providing a way to access/change the values in the maps of the struct_ops
    type.
    
    bpf_map__initial_value() will return st_ops->data for struct_ops types. The
    skeleton is going to use it as the pointer to the shadow type of the
    original struct type.
    
    One of the main differences between the original struct type and the shadow
    type is that all function pointers of the shadow type are converted to
    pointers of struct bpf_program. Users can replace these bpf_program
    pointers with other BPF programs. The st_ops->progs[] will be updated
    before updating the value of a map to reflect the changes made by users.
    
    Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
    Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20240229064523.2091270-3-thinker.li@xxxxxxxxx
    Stable-dep-of: 04a94133f1b3 ("libbpf: Don't take direct pointers into BTF data from st_ops")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a2b765e419c16..c91917868b557 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -994,6 +994,19 @@ static bool bpf_map__is_struct_ops(const struct bpf_map *map)
 	return map->def.type == BPF_MAP_TYPE_STRUCT_OPS;
 }
 
+static bool is_valid_st_ops_program(struct bpf_object *obj,
+				    const struct bpf_program *prog)
+{
+	int i;
+
+	for (i = 0; i < obj->nr_programs; i++) {
+		if (&obj->programs[i] == prog)
+			return prog->type == BPF_PROG_TYPE_STRUCT_OPS;
+	}
+
+	return false;
+}
+
 /* Init the map's fields that depend on kern_btf */
 static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
 {
@@ -1082,9 +1095,16 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
 		if (btf_is_ptr(mtype)) {
 			struct bpf_program *prog;
 
-			prog = st_ops->progs[i];
+			/* Update the value from the shadow type */
+			prog = *(void **)mdata;
+			st_ops->progs[i] = prog;
 			if (!prog)
 				continue;
+			if (!is_valid_st_ops_program(obj, prog)) {
+				pr_warn("struct_ops init_kern %s: member %s is not a struct_ops program\n",
+					map->name, mname);
+				return -ENOTSUP;
+			}
 
 			kern_mtype = skip_mods_and_typedefs(kern_btf,
 							    kern_mtype->type,
@@ -9165,7 +9185,9 @@ static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj,
 	return NULL;
 }
 
-/* Collect the reloc from ELF and populate the st_ops->progs[] */
+/* Collect the reloc from ELF, populate the st_ops->progs[], and update
+ * st_ops->data for shadow type.
+ */
 static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
 					    Elf64_Shdr *shdr, Elf_Data *data)
 {
@@ -9279,6 +9301,14 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
 		}
 
 		st_ops->progs[member_idx] = prog;
+
+		/* st_ops->data will be exposed to users, being returned by
+		 * bpf_map__initial_value() as a pointer to the shadow
+		 * type. All function pointers in the original struct type
+		 * should be converted to a pointer to struct bpf_program
+		 * in the shadow type.
+		 */
+		*((struct bpf_program **)(st_ops->data + moff)) = prog;
 	}
 
 	return 0;
@@ -9730,6 +9760,12 @@ int bpf_map__set_initial_value(struct bpf_map *map,
 
 void *bpf_map__initial_value(struct bpf_map *map, size_t *psize)
 {
+	if (bpf_map__is_struct_ops(map)) {
+		if (psize)
+			*psize = map->def.value_size;
+		return map->st_ops->data;
+	}
+
 	if (!map->mmaped)
 		return NULL;
 	*psize = map->def.value_size;