On Mon, Jan 27, 2025 at 2:27 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
>
> From: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
>
> In commit 1611603537a4 ("bpf: Create argument information for nullable arguments."),
> it introduced a "__nullable" tagging at the argument name of a
> stub function. Some background on the commit:
> it requires to tag the stub function instead of directly tagging
> the "ops" of a struct. This is because the btf func_proto of the "ops"
> does not have the argument name and the "__nullable" is tagged at
> the argument name.
>
> To find the stub function of a "ops", it currently relies on a naming
> convention on the stub function "st_ops__ops_name".
> e.g. tcp_congestion_ops__ssthresh. However, the new kernel
> sub system implementing bpf_struct_ops have missed this and
> have been surprised that the "__nullable" and the to-be-landed
> "__ref" tagging was not effective.
>
> One option would be to give a warning whenever the stub function does
> not follow the naming convention, regardless if it requires arg tagging
> or not.
>
> Instead, this patch uses the kallsyms_lookup approach and removes
> the requirement on the naming convention. The st_ops->cfi_stubs has
> all the stub function kernel addresses. kallsyms_lookup() is used to
> lookup the function name. With the function name, BTF can be used to
> find the BTF func_proto. The existing "__nullable" arg name searching
> logic will then fall through.
>
> One notable change is,
> if it failed in kallsyms_lookup or it failed in looking up the stub
> function name from the BTF, the bpf_struct_ops registration will fail.
> This is different from the previous behavior that it silently ignored
> the "st_ops__ops_name" function not found error.
>
> The "tcp_congestion_ops", "sched_ext_ops", and "hid_bpf_ops" can still be
> registered successfully after this patch. There is struct_ops_maybe_null
> selftest to cover the "__nullable" tagging.
>
The patch looks good to me. Also tested with selftests in the qdisc
set and they passed.
Reviewed-by: Amery Hung <ameryhung@xxxxxxxxx>
> Other minor changes:
> 1. Removed the "%s__%s" format from the pr_warn because the naming
> convention is removed.
> 2. The existing bpf_struct_ops_supported() is also moved earlier
> because prepare_arg_info needs to use it to decide if the
> stub function is NULL before calling the prepare_arg_info.
>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Benjamin Tissoires <bentiss@xxxxxxxxxx>
> Cc: Yonghong Song <yonghong.song@xxxxxxxxx>
> Cc: Amery Hung <ameryhung@xxxxxxxxx>
> Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
> ---
> kernel/bpf/bpf_struct_ops.c | 98 +++++++++++++++++--------------------
> 1 file changed, 44 insertions(+), 54 deletions(-)
>
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 040fb1cd840b..9b7f3b9c5262 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -146,39 +146,6 @@ void bpf_struct_ops_image_free(void *image)
> }
>
> #define MAYBE_NULL_SUFFIX "__nullable"
> -#define MAX_STUB_NAME 128
> -
> -/* Return the type info of a stub function, if it exists.
> - *
> - * The name of a stub function is made up of the name of the struct_ops and
> - * the name of the function pointer member, separated by "__". For example,
> - * if the struct_ops type is named "foo_ops" and the function pointer
> - * member is named "bar", the stub function name would be "foo_ops__bar".
> - */
> -static const struct btf_type *
> -find_stub_func_proto(const struct btf *btf, const char *st_op_name,
> - const char *member_name)
> -{
> - char stub_func_name[MAX_STUB_NAME];
> - const struct btf_type *func_type;
> - s32 btf_id;
> - int cp;
> -
> - cp = snprintf(stub_func_name, MAX_STUB_NAME, "%s__%s",
> - st_op_name, member_name);
> - if (cp >= MAX_STUB_NAME) {
> - pr_warn("Stub function name too long\n");
> - return NULL;
> - }
> - btf_id = btf_find_by_name_kind(btf, stub_func_name, BTF_KIND_FUNC);
> - if (btf_id < 0)
> - return NULL;
> - func_type = btf_type_by_id(btf, btf_id);
> - if (!func_type)
> - return NULL;
> -
> - return btf_type_by_id(btf, func_type->type); /* FUNC_PROTO */
> -}
>
> /* Prepare argument info for every nullable argument of a member of a
> * struct_ops type.
> @@ -203,27 +170,42 @@ find_stub_func_proto(const struct btf *btf, const char *st_op_name,
> static int prepare_arg_info(struct btf *btf,
> const char *st_ops_name,
> const char *member_name,
> - const struct btf_type *func_proto,
> + const struct btf_type *func_proto, void *stub_func_addr,
> struct bpf_struct_ops_arg_info *arg_info)
> {
> const struct btf_type *stub_func_proto, *pointed_type;
> const struct btf_param *stub_args, *args;
> struct bpf_ctx_arg_aux *info, *info_buf;
> u32 nargs, arg_no, info_cnt = 0;
> + char ksym[KSYM_SYMBOL_LEN];
> + const char *stub_fname;
> + s32 stub_func_id;
> u32 arg_btf_id;
> int offset;
>
> - stub_func_proto = find_stub_func_proto(btf, st_ops_name, member_name);
> - if (!stub_func_proto)
> - return 0;
> + stub_fname = kallsyms_lookup((unsigned long)stub_func_addr, NULL, NULL, NULL, ksym);
> + if (!stub_fname) {
> + pr_warn("Cannot find the stub function name for the %s in struct %s\n",
> + member_name, st_ops_name);
> + return -ENOENT;
> + }
> +
> + stub_func_id = btf_find_by_name_kind(btf, stub_fname, BTF_KIND_FUNC);
> + if (stub_func_id < 0) {
> + pr_warn("Cannot find the stub function %s in btf\n", stub_fname);
> + return -ENOENT;
> + }
> +
> + stub_func_proto = btf_type_by_id(btf, stub_func_id);
> + stub_func_proto = btf_type_by_id(btf, stub_func_proto->type);
>
> /* Check if the number of arguments of the stub function is the same
> * as the number of arguments of the function pointer.
> */
> nargs = btf_type_vlen(func_proto);
> if (nargs != btf_type_vlen(stub_func_proto)) {
> - pr_warn("the number of arguments of the stub function %s__%s does not match the number of arguments of the member %s of struct %s\n",
> - st_ops_name, member_name, member_name, st_ops_name);
> + pr_warn("the number of arguments of the stub function %s does not match the number of arguments of the member %s of struct %s\n",
> + stub_fname, member_name, st_ops_name);
> return -EINVAL;
> }
>
> @@ -253,21 +235,21 @@ static int prepare_arg_info(struct btf *btf,
> &arg_btf_id);
> if (!pointed_type ||
> !btf_type_is_struct(pointed_type)) {
> - pr_warn("stub function %s__%s has %s tagging to an unsupported type\n",
> - st_ops_name, member_name, MAYBE_NULL_SUFFIX);
> + pr_warn("stub function %s has %s tagging to an unsupported type\n",
> + stub_fname, MAYBE_NULL_SUFFIX);
> goto err_out;
> }
>
> offset = btf_ctx_arg_offset(btf, func_proto, arg_no);
> if (offset < 0) {
> - pr_warn("stub function %s__%s has an invalid trampoline ctx offset for arg#%u\n",
> - st_ops_name, member_name, arg_no);
> + pr_warn("stub function %s has an invalid trampoline ctx offset for arg#%u\n",
> + stub_fname, arg_no);
> goto err_out;
> }
>
> if (args[arg_no].type != stub_args[arg_no].type) {
> - pr_warn("arg#%u type in stub function %s__%s does not match with its original func_proto\n",
> - arg_no, st_ops_name, member_name);
> + pr_warn("arg#%u type in stub function %s does not match with its original func_proto\n",
> + arg_no, stub_fname);
> goto err_out;
> }
>
> @@ -324,6 +306,13 @@ 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);
> +
> + return func_ptr ? 0 : -ENOTSUPP;
> +}
> +
> int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
> struct btf *btf,
> struct bpf_verifier_log *log)
> @@ -387,7 +376,10 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
>
> for_each_member(i, t, member) {
> const struct btf_type *func_proto;
> + void **stub_func_addr;
> + u32 moff;
>
> + moff = __btf_member_bit_offset(t, member) / 8;
> mname = btf_name_by_offset(btf, member->name_off);
> if (!*mname) {
> pr_warn("anon member in struct %s is not supported\n",
> @@ -413,7 +405,11 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
> func_proto = btf_type_resolve_func_ptr(btf,
> member->type,
> NULL);
> - if (!func_proto)
> +
> + /* The member is not a function pointer or
> + * the function pointer is not supported.
> + */
> + if (!func_proto || bpf_struct_ops_supported(st_ops, moff))
> continue;
>
> if (btf_distill_func_proto(log, btf,
> @@ -425,8 +421,9 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
> goto errout;
> }
>
> + stub_func_addr = *(void **)(st_ops->cfi_stubs + moff);
> err = prepare_arg_info(btf, st_ops->name, mname,
> - func_proto,
> + func_proto, stub_func_addr,
> arg_info + i);
> if (err)
> goto errout;
> @@ -1152,13 +1149,6 @@ void bpf_struct_ops_put(const void *kdata)
> bpf_map_put(&st_map->map);
> }
>
> -int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
> -{
> - void *func_ptr = *(void **)(st_ops->cfi_stubs + moff);
> -
> - return func_ptr ? 0 : -ENOTSUPP;
> -}
> -
> static bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
> {
> struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
> --
> 2.43.5
>
