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Date: Mon, 23 May 2022 20:48:57 -0700
From: Martin KaFai Lau <kafai@...com>
To: Stanislav Fomichev <sdf@...gle.com>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v7 05/11] bpf: implement BPF_PROG_QUERY for
BPF_LSM_CGROUP
On Wed, May 18, 2022 at 03:55:25PM -0700, Stanislav Fomichev wrote:
> We have two options:
> 1. Treat all BPF_LSM_CGROUP the same, regardless of attach_btf_id
> 2. Treat BPF_LSM_CGROUP+attach_btf_id as a separate hook point
>
> I was doing (2) in the original patch, but switching to (1) here:
>
> * bpf_prog_query returns all attached BPF_LSM_CGROUP programs
> regardless of attach_btf_id
> * attach_btf_id is exported via bpf_prog_info
>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
> include/uapi/linux/bpf.h | 5 ++
> kernel/bpf/cgroup.c | 103 +++++++++++++++++++++++++++------------
> kernel/bpf/syscall.c | 4 +-
> 3 files changed, 81 insertions(+), 31 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index b9d2d6de63a7..432fc5f49567 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1432,6 +1432,7 @@ union bpf_attr {
> __u32 attach_flags;
> __aligned_u64 prog_ids;
> __u32 prog_cnt;
> + __aligned_u64 prog_attach_flags; /* output: per-program attach_flags */
> } query;
>
> struct { /* anonymous struct used by BPF_RAW_TRACEPOINT_OPEN command */
> @@ -5911,6 +5912,10 @@ struct bpf_prog_info {
> __u64 run_cnt;
> __u64 recursion_misses;
> __u32 verified_insns;
> + /* BTF ID of the function to attach to within BTF object identified
> + * by btf_id.
> + */
> + __u32 attach_btf_func_id;
> } __attribute__((aligned(8)));
>
> struct bpf_map_info {
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index a959cdd22870..08a1015ee09e 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1074,6 +1074,7 @@ static int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
> static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
> union bpf_attr __user *uattr)
> {
> + __u32 __user *prog_attach_flags = u64_to_user_ptr(attr->query.prog_attach_flags);
> __u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
> enum bpf_attach_type type = attr->query.attach_type;
> enum cgroup_bpf_attach_type atype;
> @@ -1081,50 +1082,92 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
> struct hlist_head *progs;
> struct bpf_prog *prog;
> int cnt, ret = 0, i;
> + int total_cnt = 0;
> u32 flags;
>
> - atype = to_cgroup_bpf_attach_type(type);
> - if (atype < 0)
> - return -EINVAL;
> + enum cgroup_bpf_attach_type from_atype, to_atype;
>
> - progs = &cgrp->bpf.progs[atype];
> - flags = cgrp->bpf.flags[atype];
> + if (type == BPF_LSM_CGROUP) {
> + from_atype = CGROUP_LSM_START;
> + to_atype = CGROUP_LSM_END;
> + } else {
> + from_atype = to_cgroup_bpf_attach_type(type);
> + if (from_atype < 0)
> + return -EINVAL;
> + to_atype = from_atype;
> + }
>
> - effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> - lockdep_is_held(&cgroup_mutex));
> + for (atype = from_atype; atype <= to_atype; atype++) {
> + progs = &cgrp->bpf.progs[atype];
> + flags = cgrp->bpf.flags[atype];
>
> - if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> - cnt = bpf_prog_array_length(effective);
> - else
> - cnt = prog_list_length(progs);
> + effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> + lockdep_is_held(&cgroup_mutex));
>
> - if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
> - return -EFAULT;
> - if (copy_to_user(&uattr->query.prog_cnt, &cnt, sizeof(cnt)))
> + if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> + total_cnt += bpf_prog_array_length(effective);
> + else
> + total_cnt += prog_list_length(progs);
> + }
> +
> + if (type != BPF_LSM_CGROUP)
> + if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
> + return -EFAULT;
> + if (copy_to_user(&uattr->query.prog_cnt, &total_cnt, sizeof(total_cnt)))
> return -EFAULT;
> - if (attr->query.prog_cnt == 0 || !prog_ids || !cnt)
> + if (attr->query.prog_cnt == 0 || !prog_ids || !total_cnt)
> /* return early if user requested only program count + flags */
> return 0;
> - if (attr->query.prog_cnt < cnt) {
> - cnt = attr->query.prog_cnt;
> +
> + if (attr->query.prog_cnt < total_cnt) {
> + total_cnt = attr->query.prog_cnt;
> ret = -ENOSPC;
> }
>
> - if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
> - return bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
> - } else {
> - struct bpf_prog_list *pl;
> - u32 id;
> + for (atype = from_atype; atype <= to_atype; atype++) {
> + if (total_cnt <= 0)
> + break;
>
> - i = 0;
> - hlist_for_each_entry(pl, progs, node) {
> - prog = prog_list_prog(pl);
> - id = prog->aux->id;
> - if (copy_to_user(prog_ids + i, &id, sizeof(id)))
> - return -EFAULT;
> - if (++i == cnt)
> - break;
> + progs = &cgrp->bpf.progs[atype];
> + flags = cgrp->bpf.flags[atype];
> +
> + effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> + lockdep_is_held(&cgroup_mutex));
> +
> + if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> + cnt = bpf_prog_array_length(effective);
> + else
> + cnt = prog_list_length(progs);
> +
> + if (cnt >= total_cnt)
> + cnt = total_cnt;
> +
> + if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
> + ret = bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
> + } else {
> + struct bpf_prog_list *pl;
> + u32 id;
> +
> + i = 0;
> + hlist_for_each_entry(pl, progs, node) {
> + prog = prog_list_prog(pl);
> + id = prog->aux->id;
> + if (copy_to_user(prog_ids + i, &id, sizeof(id)))
> + return -EFAULT;
> + if (++i == cnt)
> + break;
> + }
> }
> +
> + if (prog_attach_flags)
> + for (i = 0; i < cnt; i++)
> + if (copy_to_user(prog_attach_flags + i, &flags, sizeof(flags)))
> + return -EFAULT;
> +
> + prog_ids += cnt;
> + total_cnt -= cnt;
> + if (prog_attach_flags)
> + prog_attach_flags += cnt;
> }
> return ret;
> }
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 5ed2093e51cc..4137583c04a2 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3520,7 +3520,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
> }
> }
>
> -#define BPF_PROG_QUERY_LAST_FIELD query.prog_cnt
> +#define BPF_PROG_QUERY_LAST_FIELD query.prog_attach_flags
>
> static int bpf_prog_query(const union bpf_attr *attr,
> union bpf_attr __user *uattr)
> @@ -3556,6 +3556,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
> case BPF_CGROUP_SYSCTL:
> case BPF_CGROUP_GETSOCKOPT:
> case BPF_CGROUP_SETSOCKOPT:
> + case BPF_LSM_CGROUP:
> return cgroup_bpf_prog_query(attr, uattr);
> case BPF_LIRC_MODE2:
> return lirc_prog_query(attr, uattr);
> @@ -4066,6 +4067,7 @@ static int bpf_prog_get_info_by_fd(struct file *file,
>
> if (prog->aux->btf)
> info.btf_id = btf_obj_id(prog->aux->btf);
> + info.attach_btf_func_id = prog->aux->attach_btf_id;
Note that exposing prog->aux->attach_btf_id only may not be enough
unless it can assume info.attach_btf_id is always referring to btf_vmlinux
for all bpf prog types.
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