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bpf: Enable task local storage for tracing programs

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To access per-task data, BPF programs usually creates a hash table with
pid as the key. This is not ideal because:
 1. The user need to estimate the proper size of the hash table, which may
    be inaccurate;
 2. Big hash tables are slow;
 3. To clean up the data properly during task terminations, the user need
    to write extra logic.

Task local storage overcomes these issues and offers a better option for
these per-task data. Task local storage is only available to BPF_LSM. Now
enable it for tracing programs.

Unlike LSM programs, tracing programs can be called in IRQ contexts.
Helpers that access task local storage are updated to use
raw_spin_lock_irqsave() instead of raw_spin_lock_bh().

Tracing programs can attach to functions on the task free path, e.g.
exit_creds(). To avoid allocating task local storage after
bpf_task_storage_free(). bpf_task_storage_get() is updated to not allocate
new storage when the task is not refcounted (task->usage == 0).

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: KP Singh <kpsingh@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210225234319.336131-2-songliubraving@fb.com
This commit is contained in:
Song Liu 2021-02-25 15:43:14 -08:00 • committed by Alexei Starovoitov
parent 9c8f21e6f8
commit a10787e6d5
10 changed files with 51 additions and 72 deletions
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22
include/linux/bpf_lsm.h
View file

@ -38,21 +38,9 @@ static inline struct bpf_storage_blob *bpf_inode(
return inode->i_security + bpf_lsm_blob_sizes.lbs_inode;
}
static inline struct bpf_storage_blob *bpf_task(
const struct task_struct *task)
{
if (unlikely(!task->security))
return NULL;
return task->security + bpf_lsm_blob_sizes.lbs_task;
}
extern const struct bpf_func_proto bpf_inode_storage_get_proto;
extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
extern const struct bpf_func_proto bpf_task_storage_get_proto;
extern const struct bpf_func_proto bpf_task_storage_delete_proto;
void bpf_inode_storage_free(struct inode *inode);
void bpf_task_storage_free(struct task_struct *task);
#else /* !CONFIG_BPF_LSM */
@ -73,20 +61,10 @@ static inline struct bpf_storage_blob *bpf_inode(
return NULL;
}
static inline struct bpf_storage_blob *bpf_task(
const struct task_struct *task)
{
return NULL;
}
static inline void bpf_inode_storage_free(struct inode *inode)
{
}
static inline void bpf_task_storage_free(struct task_struct *task)
{
}
#endif /* CONFIG_BPF_LSM */
#endif /* _LINUX_BPF_LSM_H */