Re: Proposal: bpf_copy_from_user_remote

[Kenny Yu <kennyyu@fb.com>]

Hi Gabriele,

I just submitted a patch series that adds a similar helper to read
userspace memory from a remote process, please see: https://lore.kernel.org/bpf/20220113233158.1582743-1-kennyyu@fb.com/T/#ma0646f96bccf0b957793054de7404115d321079d

In my patch series, I added a bpf helper to wrap `access_process_vm`
which takes a `struct task_struct` argument instead of a pid.

In your patch series, one issue would be it is not clear which pid namespace
the pid belongs to, whereas passing a `struct task_struct` is unambiguous.
I think the helper signature in my patch series also provides more flexibility,
as the bpf program can also provide different flags on how to read
userspace memory.

Our use case at Meta for this change is to use a bpf task iterator program
to read debug information from a running process in production, e.g.,
extract C++ async stack traces from a running program.

A few questions:
* What is your use case for adding this helper?
* Do you have a specific requirement that requires using a pid, or would a
  helper using `struct task_struct` be sufficient?
* Are you ok with these changes? If so, I will proceed with my patch series.

Thanks,
Kenny Yu