> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 6ae7262ebe0c..e0c5c643fe9e 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
[ ... ]
> @@ -254,6 +254,11 @@ static const struct btf_type *find_type_for_map(struct
> btf *btf, const char *map
> return NULL;
> }
>
> +static bool bpf_map_is_percpu_data(const struct bpf_map *map)
> +{
> + return bpf_map__is_internal(map) && bpf_map__type(map) ==
> BPF_MAP_TYPE_PERCPU_ARRAY;
> +}
> +
[ ... ]
> @@ -847,7 +851,7 @@ static int gen_trace(struct bpf_object *obj, const char
> *obj_name, const char *h
> bpf_object__for_each_map(map, obj) {
> const char *mmap_flags;
>
> - if (!is_mmapable_map(map, ident, sizeof(ident)))
> + if (!is_mmapable_map(map, ident, sizeof(ident)) ||
> bpf_map_is_percpu_data(map))
> continue;
By skipping the .percpu map here during light skeleton generation in
gen_trace(), is the user-space buffer for .percpu left writable?
If a user modifies skel->percpu after the light skeleton is loaded, will
that silently succeed without actually updating the kernel per-cpu map?
The regular skeleton path appears protected, since libbpf mprotect()s the
percpu mmaped buffer read-only at load in bpf_object__populate_internal_map().
For the light skeleton, gen_trace() skips the .percpu map, so its initial
value buffer is never finalized with skel_finalize_map_data() and never
mprotect()'d to PROT_READ, leaving it writable.
Does the generated light skeleton need an explicit mprotect(..., PROT_READ)
on the .percpu initial value buffer to enforce the read-only constraint
described in the commit message?
This was raised on v4
(https://lore.kernel.org/bpf/[email protected]/)
where the response was that the mprotect(..., PROT_READ) added in patch #4
should be moved into this patch so it isn't missed. The v5 code here looks
unchanged from v4, and the mprotect does not appear to have been moved in.
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/27147120330
