tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Copyright (c) 2020 Facebook */
   3 #include <vmlinux.h>
   4 #include <bpf/bpf_helpers.h>
   5
   6 char _license[] SEC("license") = "GPL";
   7
   8 #define MAX_STACK_TRACE_DEPTH   64
   9 unsigned long entries[MAX_STACK_TRACE_DEPTH] = {};
  10 #define SIZE_OF_ULONG (sizeof(unsigned long))
  11
  12 SEC("iter/task")
  13 int dump_task_stack(struct bpf_iter__task *ctx)
  14 {
  15         struct seq_file *seq = ctx->meta->seq;
  16         struct task_struct *task = ctx->task;
  17         long i, retlen;
  18
  19         if (task == (void *)0)
  20                 return 0;
  21
  22         retlen = bpf_get_task_stack(task, entries,
  23                                     MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, 0);
  24         if (retlen < 0)
  25                 return 0;
  26
  27         BPF_SEQ_PRINTF(seq, "pid: %8u num_entries: %8u\n", task->pid,
  28                        retlen / SIZE_OF_ULONG);
  29         for (i = 0; i < MAX_STACK_TRACE_DEPTH; i++) {
  30                 if (retlen > i * SIZE_OF_ULONG)
  31                         BPF_SEQ_PRINTF(seq, "[<0>] %pB\n", (void *)entries[i]);
  32         }
  33         BPF_SEQ_PRINTF(seq, "\n");
  34
  35         return 0;
  36 }
  37
  38 int num_user_stacks = 0;
  39
  40 SEC("iter/task")
  41 int get_task_user_stacks(struct bpf_iter__task *ctx)
  42 {
  43         struct seq_file *seq = ctx->meta->seq;
  44         struct task_struct *task = ctx->task;
  45         uint64_t buf_sz = 0;
  46         int64_t res;
  47
  48         if (task == (void *)0)
  49                 return 0;
  50
  51         res = bpf_get_task_stack(task, entries,
  52                         MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, BPF_F_USER_STACK);
  53         if (res <= 0)
  54                 return 0;
  55
  56         /* Only one task, the current one, should succeed */
  57         ++num_user_stacks;
  58
  59         buf_sz += res;
  60
  61         /* If the verifier doesn't refine bpf_get_task_stack res, and instead
  62          * assumes res is entirely unknown, this program will fail to load as
  63          * the verifier will believe that max buf_sz value allows reading
  64          * past the end of entries in bpf_seq_write call
  65          */
  66         bpf_seq_write(seq, &entries, buf_sz);
  67         return 0;
  68 }