On 8/11/23 16:27, Kui-Feng Lee wrote:
On 8/11/23 16:05, Stanislav Fomichev wrote:
On 08/10, thinker.li@xxxxxxxxx wrote:
From: Kui-Feng Lee <kuifeng@xxxxxxxx>
Provide bpf_copy_from_user() and bpf_copy_to_user() to the BPF programs
attached to cgroup/{set,get}sockopt. bpf_copy_to_user() is a new
kfunc to
copy data from an kernel space buffer to a user space buffer. They
are only
available for sleepable BPF programs. bpf_copy_to_user() is only
available
to the BPF programs attached to cgroup/getsockopt.
Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
---
kernel/bpf/cgroup.c | 6 ++++++
kernel/bpf/helpers.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 37 insertions(+)
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 5bf3115b265c..c15a72860d2a 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -2461,6 +2461,12 @@ cg_sockopt_func_proto(enum bpf_func_id
func_id, const struct bpf_prog *prog)
#endif
case BPF_FUNC_perf_event_output:
return &bpf_event_output_data_proto;
+
+ case BPF_FUNC_copy_from_user:
+ if (prog->aux->sleepable)
+ return &bpf_copy_from_user_proto;
+ return NULL;
If we just allow copy to/from, I'm not sure I understand how the buffer
sharing between sleepable/non-sleepable works.
Let's assume I have two progs in the chain:
1. non-sleepable - copies the buffer, does some modifications; since
we don't copy the buffer back after every prog run, the modifications
stay in the kernel buffer
2. sleepable - runs and just gets the user pointer? does it mean this
sleepable program doesn't see the changes from (1)?
It is still visible from sleepable programs. Sleepable programs
will receive a pointer to the buffer in the kernel.
And, BPF_SOCKOPT_FLAG_OPTVAL_USER is clear.
IOW, do we need some custom sockopt copy_to/from that handle this
potential buffer location transparently or am I missing something?
Assuming we want to support this at all. If we do, might deserve a
selftest.
It is why BPF_SOCKOPT_FLAG_OPTVAL_USER is there.
It helps programs to make a right decision.
However, I am going to remove bpf_copy_from_user()
since we have bpf_so_optval_copy_to() and bpf_so_optval_copy_to_r().
Does it make sense to you?
