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 #include "bpf_misc.h"
9
10 char _license[] SEC("license") = "GPL";
11
12 /* typically virtio scsi has max SGs of 6 */
13 #define VIRTIO_MAX_SGS 6
14
15 /* Verifier will fail with SG_MAX = 128. The failure can be
16 * workarounded with a smaller SG_MAX, e.g. 10.
17 */
18 #define WORKAROUND
19 #ifdef WORKAROUND
20 #define SG_MAX 10
21 #else
22 /* typically virtio blk has max SEG of 128 */
23 #define SG_MAX 128
24 #endif
25
26 #define SG_CHAIN 0x01UL
27 #define SG_END 0x02UL
28
29 struct scatterlist {
30 unsigned long page_link;
31 unsigned int offset;
32 unsigned int length;
33 };
34
35 #define sg_is_chain(sg) ((sg)->page_link & SG_CHAIN)
36 #define sg_is_last(sg) ((sg)->page_link & SG_END)
37 #define sg_chain_ptr(sg) \
38 ((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
39
__sg_next(struct scatterlist * sgp)40 static inline struct scatterlist *__sg_next(struct scatterlist *sgp)
41 {
42 struct scatterlist sg;
43
44 bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
45 if (sg_is_last(&sg))
46 return NULL;
47
48 sgp++;
49
50 bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
51 if (sg_is_chain(&sg))
52 sgp = sg_chain_ptr(&sg);
53
54 return sgp;
55 }
56
get_sgp(struct scatterlist ** sgs,int i)57 static inline struct scatterlist *get_sgp(struct scatterlist **sgs, int i)
58 {
59 struct scatterlist *sgp;
60
61 bpf_probe_read_kernel(&sgp, sizeof(sgp), sgs + i);
62 return sgp;
63 }
64
65 int config = 0;
66 int result = 0;
67
68 SEC("kprobe/virtqueue_add_sgs")
BPF_KPROBE(trace_virtqueue_add_sgs,void * unused,struct scatterlist ** sgs,unsigned int out_sgs,unsigned int in_sgs)69 int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs,
70 unsigned int out_sgs, unsigned int in_sgs)
71 {
72 struct scatterlist *sgp = NULL;
73 __u64 length1 = 0, length2 = 0;
74 unsigned int i, n, len;
75
76 if (config != 0)
77 return 0;
78
79 for (i = 0; (i < VIRTIO_MAX_SGS) && (i < out_sgs); i++) {
80 __sink(out_sgs);
81 for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
82 sgp = __sg_next(sgp)) {
83 bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
84 length1 += len;
85 n++;
86 }
87 }
88
89 for (i = 0; (i < VIRTIO_MAX_SGS) && (i < in_sgs); i++) {
90 __sink(in_sgs);
91 for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
92 sgp = __sg_next(sgp)) {
93 bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
94 length2 += len;
95 n++;
96 }
97 }
98
99 config = 1;
100 result = length2 - length1;
101 return 0;
102 }
103