1// SPDX-License-Identifier: GPL-2.0
 2
 3#include <linux/ptrace.h>
 4#include <stddef.h>
 5#include <linux/bpf.h>
 6#include <bpf/bpf_helpers.h>
 7#include <bpf/bpf_tracing.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
28struct scatterlist {
29	unsigned long   page_link;
30	unsigned int    offset;
31	unsigned int    length;
32};
33
34#define sg_is_chain(sg)		((sg)->page_link & SG_CHAIN)
35#define sg_is_last(sg)		((sg)->page_link & SG_END)
36#define sg_chain_ptr(sg)	\
37	((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
38
39static inline struct scatterlist *__sg_next(struct scatterlist *sgp)
40{
41	struct scatterlist sg;
42
43	bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
44	if (sg_is_last(&sg))
45		return NULL;
46
47	sgp++;
48
49	bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
50	if (sg_is_chain(&sg))
51		sgp = sg_chain_ptr(&sg);
52
53	return sgp;
54}
55
56static inline struct scatterlist *get_sgp(struct scatterlist **sgs, int i)
57{
58	struct scatterlist *sgp;
59
60	bpf_probe_read_kernel(&sgp, sizeof(sgp), sgs + i);
61	return sgp;
62}
63
64int config = 0;
65int result = 0;
66
67SEC("kprobe/virtqueue_add_sgs")
68int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs,
69	       unsigned int out_sgs, unsigned int in_sgs)
70{
71	struct scatterlist *sgp = NULL;
72	__u64 length1 = 0, length2 = 0;
73	unsigned int i, n, len;
74
75	if (config != 0)
76		return 0;
77
78	for (i = 0; (i < VIRTIO_MAX_SGS) && (i < out_sgs); i++) {
79		for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
80		     sgp = __sg_next(sgp)) {
81			bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
82			length1 += len;
83			n++;
84		}
85	}
86
87	for (i = 0; (i < VIRTIO_MAX_SGS) && (i < in_sgs); i++) {
88		for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
89		     sgp = __sg_next(sgp)) {
90			bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
91			length2 += len;
92			n++;
93		}
94	}
95
96	config = 1;
97	result = length2 - length1;
98	return 0;
99}