LXR linux/tools/testing/selftests/bpf/progs/loop6.c

   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}
 100