diff options
| author | Yonghong Song <yhs@fb.com> | 2022-12-03 10:46:02 -0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-12-04 12:52:40 -0800 |
| commit | fca1aa75518c03b04c3c249e9a9134faf9ca18c5 (patch) | |
| tree | 5981ba7fb846f4f58f1210a03cee3058bb86354c /kernel/bpf/helpers.c | |
| parent | 706819495921ddad6b3780140b9d9e9293b6dedc (diff) | |
bpf: Handle MEM_RCU type properly
Commit 9bb00b2895cb ("bpf: Add kfunc bpf_rcu_read_lock/unlock()")
introduced MEM_RCU and bpf_rcu_read_lock/unlock() support. In that
commit, a rcu pointer is tagged with both MEM_RCU and PTR_TRUSTED
so that it can be passed into kfuncs or helpers as an argument.
Martin raised a good question in [1] such that the rcu pointer,
although being able to accessing the object, might have reference
count of 0. This might cause a problem if the rcu pointer is passed
to a kfunc which expects trusted arguments where ref count should
be greater than 0.
This patch makes the following changes related to MEM_RCU pointer:
- MEM_RCU pointer might be NULL (PTR_MAYBE_NULL).
- Introduce KF_RCU so MEM_RCU ptr can be acquired with
a KF_RCU tagged kfunc which assumes ref count of rcu ptr
could be zero.
- For mem access 'b = ptr->a', say 'ptr' is a MEM_RCU ptr, and
'a' is tagged with __rcu as well. Let us mark 'b' as
MEM_RCU | PTR_MAYBE_NULL.
[1] https://lore.kernel.org/bpf/ac70f574-4023-664e-b711-e0d3b18117fd@linux.dev/
Fixes: 9bb00b2895cb ("bpf: Add kfunc bpf_rcu_read_lock/unlock()")
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221203184602.477272-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/helpers.c')
| -rw-r--r-- | kernel/bpf/helpers.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index a5a511430f2a..cca642358e80 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1838,6 +1838,19 @@ struct task_struct *bpf_task_acquire(struct task_struct *p) } /** + * bpf_task_acquire_not_zero - Acquire a reference to a rcu task object. A task + * acquired by this kfunc which is not stored in a map as a kptr, must be + * released by calling bpf_task_release(). + * @p: The task on which a reference is being acquired. + */ +struct task_struct *bpf_task_acquire_not_zero(struct task_struct *p) +{ + if (!refcount_inc_not_zero(&p->rcu_users)) + return NULL; + return p; +} + +/** * bpf_task_kptr_get - Acquire a reference on a struct task_struct kptr. A task * kptr acquired by this kfunc which is not subsequently stored in a map, must * be released by calling bpf_task_release(). @@ -2013,6 +2026,7 @@ BTF_ID_FLAGS(func, bpf_list_push_back) BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_list_pop_back, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, bpf_task_acquire_not_zero, KF_ACQUIRE | KF_RCU | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_task_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE) #ifdef CONFIG_CGROUPS |