103 lines · c
1// SPDX-License-Identifier: GPL-2.02 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 10char _license[] SEC("license") = "GPL";11 12/* typically virtio scsi has max SGs of 6 */13#define VIRTIO_MAX_SGS 614 15/* Verifier will fail with SG_MAX = 128. The failure can be16 * workarounded with a smaller SG_MAX, e.g. 10.17 */18#define WORKAROUND19#ifdef WORKAROUND20#define SG_MAX 1021#else22/* typically virtio blk has max SEG of 128 */23#define SG_MAX 12824#endif25 26#define SG_CHAIN 0x01UL27#define SG_END 0x02UL28 29struct 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 40static 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 57static 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 65int config = 0;66int result = 0;67 68SEC("kprobe/virtqueue_add_sgs")69int 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