bpf: introduce BPF_PROG_TYPE_PERF_EVENT program type

Introduce BPF_PROG_TYPE_PERF_EVENT programs that can be attached to
HW and SW perf events (PERF_TYPE_HARDWARE and PERF_TYPE_SOFTWARE
correspondingly in uapi/linux/perf_event.h)

The program visible context meta structure is
struct bpf_perf_event_data {
    struct pt_regs regs;
     __u64 sample_period;
};
which is accessible directly from the program:
int bpf_prog(struct bpf_perf_event_data *ctx)
{
  ... ctx->sample_period ...
  ... ctx->regs.ip ...
}

The bpf verifier rewrites the accesses into kernel internal
struct bpf_perf_event_data_kern which allows changing
struct perf_sample_data without affecting bpf programs.
New fields can be added to the end of struct bpf_perf_event_data
in the future.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 61 insertions, 0 deletions

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index ad35213b8405..d3869b03d9fe 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1,4 +1,5 @@
 /* Copyright (c) 2011-2015 PLUMgrid, http://plumgrid.com
+ * Copyright (c) 2016 Facebook
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of version 2 of the GNU General Public
@@ -8,6 +9,7 @@
 #include <linux/types.h>
 #include <linux/slab.h>
 #include <linux/bpf.h>
+#include <linux/bpf_perf_event.h>
 #include <linux/filter.h>
 #include <linux/uaccess.h>
 #include <linux/ctype.h>
@@ -552,10 +554,69 @@ static struct bpf_prog_type_list tracepoint_tl = {
 	.type	= BPF_PROG_TYPE_TRACEPOINT,
 };
 
+static bool pe_prog_is_valid_access(int off, int size, enum bpf_access_type type,
+				    enum bpf_reg_type *reg_type)
+{
+	if (off < 0 || off >= sizeof(struct bpf_perf_event_data))
+		return false;
+	if (type != BPF_READ)
+		return false;
+	if (off % size != 0)
+		return false;
+	if (off == offsetof(struct bpf_perf_event_data, sample_period)) {
+		if (size != sizeof(u64))
+			return false;
+	} else {
+		if (size != sizeof(long))
+			return false;
+	}
+	return true;
+}
+
+static u32 pe_prog_convert_ctx_access(enum bpf_access_type type, int dst_reg,
+				      int src_reg, int ctx_off,
+				      struct bpf_insn *insn_buf,
+				      struct bpf_prog *prog)
+{
+	struct bpf_insn *insn = insn_buf;
+
+	switch (ctx_off) {
+	case offsetof(struct bpf_perf_event_data, sample_period):
+		BUILD_BUG_ON(FIELD_SIZEOF(struct perf_sample_data, period) != sizeof(u64));
+		*insn++ = BPF_LDX_MEM(bytes_to_bpf_size(FIELD_SIZEOF(struct bpf_perf_event_data_kern, data)),
+				      dst_reg, src_reg,
+				      offsetof(struct bpf_perf_event_data_kern, data));
+		*insn++ = BPF_LDX_MEM(BPF_DW, dst_reg, dst_reg,
+				      offsetof(struct perf_sample_data, period));
+		break;
+	default:
+		*insn++ = BPF_LDX_MEM(bytes_to_bpf_size(FIELD_SIZEOF(struct bpf_perf_event_data_kern, regs)),
+				      dst_reg, src_reg,
+				      offsetof(struct bpf_perf_event_data_kern, regs));
+		*insn++ = BPF_LDX_MEM(bytes_to_bpf_size(sizeof(long)),
+				      dst_reg, dst_reg, ctx_off);
+		break;
+	}
+
+	return insn - insn_buf;
+}
+
+static const struct bpf_verifier_ops perf_event_prog_ops = {
+	.get_func_proto		= tp_prog_func_proto,
+	.is_valid_access	= pe_prog_is_valid_access,
+	.convert_ctx_access	= pe_prog_convert_ctx_access,
+};
+
+static struct bpf_prog_type_list perf_event_tl = {
+	.ops	= &perf_event_prog_ops,
+	.type	= BPF_PROG_TYPE_PERF_EVENT,
+};
+
 static int __init register_kprobe_prog_ops(void)
 {
 	bpf_register_prog_type(&kprobe_tl);
 	bpf_register_prog_type(&tracepoint_tl);
+	bpf_register_prog_type(&perf_event_tl);
 	return 0;
 }
 late_initcall(register_kprobe_prog_ops);