netdev - [PATCH] net: bpf: make bpf_ktime_get_ns() available to non GPL programs

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Message-Id: <20200420184750.218489-1-zenczykowski@gmail.com>
Date:   Mon, 20 Apr 2020 11:47:50 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Maciej Żenczykowski <maze@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Linux Network Development Mailing List <netdev@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>
Subject: [PATCH] net: bpf: make bpf_ktime_get_ns() available to non GPL programs

From: Maciej Żenczykowski <maze@...gle.com>

The entire implementation is in kernel/bpf/helpers.c:

BPF_CALL_0(bpf_ktime_get_ns) {
       /* NMI safe access to clock monotonic */
       return ktime_get_mono_fast_ns();
}

const struct bpf_func_proto bpf_ktime_get_ns_proto = {
       .func           = bpf_ktime_get_ns,
       .gpl_only       = false,
       .ret_type       = RET_INTEGER,
};

and this was presumably marked GPL due to kernel/time/timekeeping.c:
  EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);

and while that may make sense for kernel modules (although even that
is doubtful), there is currently AFAICT no other source of time
available to ebpf.

Furthermore this is really just equivalent to clock_gettime(CLOCK_MONOTONIC)
which is exposed to userspace (via vdso even to make it performant)...

As such, I see no reason to keep the GPL restriction.
(In the future I'd like to have access to time from Apache licensed ebpf code)

Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
---
 kernel/bpf/helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index bafc53ddd350..a5158a179e81 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -151,7 +151,7 @@ BPF_CALL_0(bpf_ktime_get_ns)
 
 const struct bpf_func_proto bpf_ktime_get_ns_proto = {
 	.func		= bpf_ktime_get_ns,
-	.gpl_only	= true,
+	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
 };
 
-- 
2.26.1.301.g55bc3eb7cb9-goog