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 9 char _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 struct 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 39 static 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 56 static 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 64 int config = 0; 65 int result = 0; 66 67 SEC("kprobe/virtqueue_add_sgs") 68 int 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