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Date: Fri, 12 Apr 2024 10:14:40 +0200
From: Benjamin Tissoires <bentiss@...nel.org>
To: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH RFC bpf-next v6 2/6] bpf: Add support for
KF_ARG_PTR_TO_TIMER
On Apr 08 2024, bentiss@...nel.org wrote:
> From: Kumar Kartikeya Dwivedi <memxor@...il.com>
>
> Introduce support for KF_ARG_PTR_TO_TIMER. The kfuncs will use bpf_timer
> as argument and that will be recognized as timer argument by verifier.
> bpf_timer_kern casting can happen inside kfunc, but using bpf_timer in
> argument makes life easier for users who work with non-kern type in BPF
> progs.
>
> Fix up process_timer_func's meta argument usage (ignore if NULL) so that
> we can share the same checks for helpers and kfuncs. meta argument is
> only needed to ensure bpf_timer_init's timer and map arguments are
> coming from the same map (map_uid logic is necessary for correct
> inner-map handling).
>
> No such concerns will be necessary for kfuncs as timer initialization
> happens using helpers, hence pass NULL to process_timer_func from kfunc
> argument handling code to ignore it.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> Signed-off-by: Benjamin Tissoires <bentiss@...nel.org>
>
> ---
>
> changes in v6:
> - used Kumar's version of the patch
> - reverted `+BTF_ID(struct, bpf_timer_kern)`
My bad. While working on bpf_wq I realized I shouldn't have touched this
part. See below:
>
> changes in v5:
> - also check for the reg offset
>
> changes in v4:
> - enforce KF_ARG_PTR_TO_TIMER to be of type PTR_TO_MAP_VALUE
>
> new in v3 (split from v2 02/10)
> ---
> kernel/bpf/verifier.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index ca6cacf7b42f..ccfe9057d8dc 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7568,12 +7568,16 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
> val + reg->off, map->record->timer_off);
> return -EINVAL;
> }
> + /* meta is only needed for bpf_timer_init to match timer and map */
> + if (!meta)
> + goto out;
> if (meta->map_ptr) {
> verbose(env, "verifier bug. Two map pointers in a timer helper\n");
> return -EFAULT;
> }
> meta->map_uid = reg->map_uid;
> meta->map_ptr = map;
> +out:
> return 0;
> }
>
> @@ -10826,6 +10830,7 @@ enum {
> KF_ARG_LIST_NODE_ID,
> KF_ARG_RB_ROOT_ID,
> KF_ARG_RB_NODE_ID,
> + KF_ARG_TIMER_ID,
> };
>
> BTF_ID_LIST(kf_arg_btf_ids)
> @@ -10834,6 +10839,7 @@ BTF_ID(struct, bpf_list_head)
> BTF_ID(struct, bpf_list_node)
> BTF_ID(struct, bpf_rb_root)
> BTF_ID(struct, bpf_rb_node)
> +BTF_ID(struct, bpf_timer_kern)
As Kumar originally put, this should be BTF_ID(struct, bpf_timer), and
he explained everything in the commit message. I was just too dumb to
understand it properly.
(Adding a comment here in case we want to extend bpf_timer API in the
future, and so this patch will be useful).
Cheers,
Benjamin
>
> static bool __is_kfunc_ptr_arg_type(const struct btf *btf,
> const struct btf_param *arg, int type)
> @@ -10877,6 +10883,11 @@ static bool is_kfunc_arg_rbtree_node(const struct btf *btf, const struct btf_par
> return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RB_NODE_ID);
> }
>
> +static bool is_kfunc_arg_timer(const struct btf *btf, const struct btf_param *arg)
> +{
> + return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_TIMER_ID);
> +}
> +
> static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf,
> const struct btf_param *arg)
> {
> @@ -10946,6 +10957,7 @@ enum kfunc_ptr_arg_type {
> KF_ARG_PTR_TO_NULL,
> KF_ARG_PTR_TO_CONST_STR,
> KF_ARG_PTR_TO_MAP,
> + KF_ARG_PTR_TO_TIMER,
> };
>
> enum special_kfunc_type {
> @@ -11102,6 +11114,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
> if (is_kfunc_arg_map(meta->btf, &args[argno]))
> return KF_ARG_PTR_TO_MAP;
>
> + if (is_kfunc_arg_timer(meta->btf, &args[argno]))
> + return KF_ARG_PTR_TO_TIMER;
> +
> if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
> if (!btf_type_is_struct(ref_t)) {
> verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
> @@ -11735,6 +11750,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> case KF_ARG_PTR_TO_CALLBACK:
> case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
> case KF_ARG_PTR_TO_CONST_STR:
> + case KF_ARG_PTR_TO_TIMER:
> /* Trusted by default */
> break;
> default:
> @@ -12021,6 +12037,15 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> if (ret)
> return ret;
> break;
> + case KF_ARG_PTR_TO_TIMER:
> + if (reg->type != PTR_TO_MAP_VALUE) {
> + verbose(env, "arg#%d doesn't point to a map value\n", i);
> + return -EINVAL;
> + }
> + ret = process_timer_func(env, regno, NULL);
> + if (ret < 0)
> + return ret;
> + break;
> }
> }
>
>
> --
> 2.44.0
>
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