[PATCH 1/5] bpf: use const pointer for struct_ops cfi_stubs

Caleb Sander Mateos
2025-12-31T17:37:23Z

struct bpf_struct_ops's cfi_stubs field is used as a readonly pointer
but has type void *. Change its type to void const * to allow it to
point to readonly global memory. Change the void ** casts of cfi_stubs
to void * const * accordingly.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
include/linux/bpf.h | 2 +-
kernel/bpf/bpf_struct_ops.c | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4e7d72dfbcd4..d74189ea1066 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1977,11 +1977,11 @@ struct bpf_struct_ops {
void *kdata, const void *udata);
int (*reg)(void *kdata, struct bpf_link *link);
void (*unreg)(void *kdata, struct bpf_link *link);
int (*update)(void *kdata, void *old_kdata, struct bpf_link *link);
int (*validate)(void *kdata);
- void *cfi_stubs;
+ void const *cfi_stubs;
struct module *owner;
const char *name;
struct btf_func_model func_models[BPF_STRUCT_OPS_MAX_NR_MEMBERS];
};

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index c43346cb3d76..42cfc3e0bc68 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -321,11 +321,11 @@ static bool is_module_member(const struct btf *btf, u32 id)
return !strcmp(btf_name_by_offset(btf, t->name_off), "module");
}

int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
{
- void *func_ptr = *(void **)(st_ops->cfi_stubs + moff);
+ void *func_ptr = *(void * const *)(st_ops->cfi_stubs + moff);

return func_ptr ? 0 : -ENOTSUPP;
}

int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
@@ -444,11 +444,11 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
mname, st_ops->name);
err = -EINVAL;
goto errout;
}

- stub_func_addr = *(void **)(st_ops->cfi_stubs + moff);
+ stub_func_addr = *(void * const *)(st_ops->cfi_stubs + moff);
err = prepare_arg_info(btf, st_ops->name, mname,
func_proto, stub_func_addr,
arg_info + i);
if (err)
goto errout;
@@ -833,11 +833,11 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
*pksym++ = ksym;

trampoline_start = image_off;
err = bpf_struct_ops_prepare_trampoline(tlinks, link,
&st_ops->func_models[i],
- *(void **)(st_ops->cfi_stubs + moff),
+ *(void * const *)(st_ops->cfi_stubs + moff),
&image, &image_off,
st_map->image_pages_cnt < MAX_TRAMP_IMAGE_PAGES);
if (err)
goto reset_unlock;

--
2.45.2