linux-kernel - [FIX bpf,perf] bpf,perf: return EOPNOTSUPP for bpf handler on PERF_COUNT_SW

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Date:   Mon, 16 Nov 2020 19:37:52 +0100
From:   Florian Lehner <dev@...-flo.net>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        john.fastabend@...il.com, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, Florian Lehner <dev@...-flo.net>
Subject: [FIX bpf,perf] bpf,perf: return EOPNOTSUPP for bpf handler on PERF_COUNT_SW_DUMMY

bpf handlers for perf events other than tracepoints, kprobes or uprobes
are attached to the overflow_handler of the perf event.

Perf events of type software/dummy are placeholder events. So when
attaching a bpf handle to an overflow_handler of such an event, the bpf
handler will not be triggered.

This fix returns the error EOPNOTSUPP to indicate that attaching a bpf
handler to a perf event of type software/dummy is not supported.

Signed-off-by: Florian Lehner <dev@...-flo.net>
---
 kernel/events/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index da467e1dd49a..4e8846b7ceda 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9668,6 +9668,10 @@ static int perf_event_set_bpf_handler(struct perf_event *event, u32 prog_fd)
 	if (event->prog)
 		return -EEXIST;
 
+	if (event->attr.type == PERF_TYPE_SOFTWARE &&
+	    event->attr.config == PERF_COUNT_SW_DUMMY)
+		return -EOPNOTSUPP;
+
 	prog = bpf_prog_get_type(prog_fd, BPF_PROG_TYPE_PERF_EVENT);
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
-- 
2.28.0