loop6.c

 1// SPDX-License-Identifier: GPL-2.0
 2
 3#include <vmlinux.h>
 4#include <bpf/bpf_core_read.h>
 5#include <bpf/bpf_helpers.h>
 6#include <bpf/bpf_tracing.h>
 7#include "bpf_misc.h"
 8
 9char _license[] SEC("license") = "GPL";
10
11/* typically virtio scsi has max SGs of 6 */
12#define VIRTIO_MAX_SGS	6
13
14/* Verifier will fail with SG_MAX = 128. The failure can be
15 * workarounded with a smaller SG_MAX, e.g. 10.
16 */
17#define WORKAROUND
18#ifdef WORKAROUND
19#define SG_MAX		10
20#else
21/* typically virtio blk has max SEG of 128 */
22#define SG_MAX		128
23#endif
24
25#define SG_CHAIN	0x01UL
26#define SG_END		0x02UL
27
28#define sg_is_chain(sg)		((sg)->page_link & SG_CHAIN)
29#define sg_is_last(sg)		((sg)->page_link & SG_END)
30#define sg_chain_ptr(sg)	\
31	((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
32
33static inline struct scatterlist *__sg_next(struct scatterlist *sgp)
34{
35	struct scatterlist sg;
36
37	bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
38	if (sg_is_last(&sg))
39		return NULL;
40
41	sgp++;
42
43	bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
44	if (sg_is_chain(&sg))
45		sgp = sg_chain_ptr(&sg);
46
47	return sgp;
48}
49
50static inline struct scatterlist *get_sgp(struct scatterlist **sgs, int i)
51{
52	struct scatterlist *sgp;
53
54	bpf_probe_read_kernel(&sgp, sizeof(sgp), sgs + i);
55	return sgp;
56}
57
58int run_once = 0;
59int result = 0;
60
61SEC("kprobe/virtqueue_add_sgs")
62int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs,
63	       unsigned int out_sgs, unsigned int in_sgs)
64{
65	struct scatterlist *sgp = NULL;
66	__u64 length1 = 0, length2 = 0;
67	unsigned int i, n, len;
68
69	if (run_once != 0)
70		return 0;
71
72	for (i = 0; (i < VIRTIO_MAX_SGS) && (i < out_sgs); i++) {
73		__sink(out_sgs);
74		for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
75		     sgp = __sg_next(sgp)) {
76			len = BPF_CORE_READ(sgp, length);
77			length1 += len;
78			n++;
79		}
80	}
81
82	for (i = 0; (i < VIRTIO_MAX_SGS) && (i < in_sgs); i++) {
83		__sink(in_sgs);
84		for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
85		     sgp = __sg_next(sgp)) {
86			len = BPF_CORE_READ(sgp, length);
87			length2 += len;
88			n++;
89		}
90	}
91
92	run_once = 1;
93	result = length2 - length1;
94	return 0;
95}