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bpf: mark mm->owner as __safe_rcu_or_null

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When CONFIG_MEMCG is enabled, we can access mm->owner under RCU. The
owner can be NULL. With this change, BPF helpers can safely access
mm->owner to retrieve the associated task from the mm. We can then make
policy decision based on the task attribute.

The typical use case is as follows,

  bpf_rcu_read_lock(); // rcu lock must be held for rcu trusted field
  @owner = @mm->owner; // mm_struct::owner is rcu trusted or null
  if (!@owner)
      goto out;

  /* Do something based on the task attribute */

out:
  bpf_rcu_read_unlock();

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/r/20251016063929.13830-2-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yafang Shao 2025-10-16 14:39:28 +08:00 committed by Alexei Starovoitov
parent c67f4ae737
commit ec8e3e27a1
1 changed files with 3 additions and 0 deletions
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3
kernel/bpf/verifier.c
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@ -7054,6 +7054,9 @@ BTF_TYPE_SAFE_RCU(struct cgroup_subsys_state) {
/* RCU trusted: these fields are trusted in RCU CS and can be NULL */
BTF_TYPE_SAFE_RCU_OR_NULL(struct mm_struct) {
struct file __rcu *exe_file;
#ifdef CONFIG_MEMCG
struct task_struct __rcu *owner;
#endif
};
/* skb->sk, req->sk are not RCU protected, but we mark them as such