1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
|
// SPDX-License-Identifier: GPL-2.0
/*
* Augment the raw_syscalls tracepoints with the contents of the pointer arguments.
*
* Test it with:
*
* perf trace -e tools/perf/examples/bpf/augmented_raw_syscalls.c cat /etc/passwd > /dev/null
*
* This exactly matches what is marshalled into the raw_syscall:sys_enter
* payload expected by the 'perf trace' beautifiers.
*
* For now it just uses the existing tracepoint augmentation code in 'perf
* trace', in the next csets we'll hook up these with the sys_enter/sys_exit
* code that will combine entry/exit in a strace like way.
*/
#include <unistd.h>
#include <pid_filter.h>
/* bpf-output associated map */
struct bpf_map SEC("maps") __augmented_syscalls__ = {
.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
.key_size = sizeof(int),
.value_size = sizeof(u32),
.max_entries = __NR_CPUS__,
};
struct syscall {
bool enabled;
};
struct bpf_map SEC("maps") syscalls = {
.type = BPF_MAP_TYPE_ARRAY,
.key_size = sizeof(int),
.value_size = sizeof(struct syscall),
.max_entries = 512,
};
struct syscall_enter_args {
unsigned long long common_tp_fields;
long syscall_nr;
unsigned long args[6];
};
struct syscall_exit_args {
unsigned long long common_tp_fields;
long syscall_nr;
long ret;
};
struct augmented_filename {
unsigned int size;
int reserved;
char value[256];
};
#define SYS_OPEN 2
#define SYS_OPENAT 257
pid_filter(pids_filtered);
SEC("raw_syscalls:sys_enter")
int sys_enter(struct syscall_enter_args *args)
{
struct {
struct syscall_enter_args args;
struct augmented_filename filename;
} augmented_args;
struct syscall *syscall;
unsigned int len = sizeof(augmented_args);
const void *filename_arg = NULL;
if (pid_filter__has(&pids_filtered, getpid()))
return 0;
probe_read(&augmented_args.args, sizeof(augmented_args.args), args);
syscall = bpf_map_lookup_elem(&syscalls, &augmented_args.args.syscall_nr);
if (syscall == NULL || !syscall->enabled)
return 0;
/*
* Yonghong and Edward Cree sayz:
*
* https://www.spinics.net/lists/netdev/msg531645.html
*
* >> R0=inv(id=0) R1=inv2 R6=ctx(id=0,off=0,imm=0) R7=inv64 R10=fp0,call_-1
* >> 10: (bf) r1 = r6
* >> 11: (07) r1 += 16
* >> 12: (05) goto pc+2
* >> 15: (79) r3 = *(u64 *)(r1 +0)
* >> dereference of modified ctx ptr R1 off=16 disallowed
* > Aha, we at least got a different error message this time.
* > And indeed llvm has done that optimisation, rather than the more obvious
* > 11: r3 = *(u64 *)(r1 +16)
* > because it wants to have lots of reads share a single insn. You may be able
* > to defeat that optimisation by adding compiler barriers, idk. Maybe someone
* > with llvm knowledge can figure out how to stop it (ideally, llvm would know
* > when it's generating for bpf backend and not do that). -O0? ¯\_(ツ)_/¯
*
* The optimization mostly likes below:
*
* br1:
* ...
* r1 += 16
* goto merge
* br2:
* ...
* r1 += 20
* goto merge
* merge:
* *(u64 *)(r1 + 0)
*
* The compiler tries to merge common loads. There is no easy way to
* stop this compiler optimization without turning off a lot of other
* optimizations. The easiest way is to add barriers:
*
* __asm__ __volatile__("": : :"memory")
*
* after the ctx memory access to prevent their down stream merging.
*/
switch (augmented_args.args.syscall_nr) {
case SYS_OPEN: filename_arg = (const void *)args->args[0];
__asm__ __volatile__("": : :"memory");
break;
case SYS_OPENAT: filename_arg = (const void *)args->args[1];
break;
}
if (filename_arg != NULL) {
augmented_args.filename.reserved = 0;
augmented_args.filename.size = probe_read_str(&augmented_args.filename.value,
sizeof(augmented_args.filename.value),
filename_arg);
if (augmented_args.filename.size < sizeof(augmented_args.filename.value)) {
len -= sizeof(augmented_args.filename.value) - augmented_args.filename.size;
len &= sizeof(augmented_args.filename.value) - 1;
}
} else {
len = sizeof(augmented_args.args);
}
perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, &augmented_args, len);
return 0;
}
SEC("raw_syscalls:sys_exit")
int sys_exit(struct syscall_exit_args *args)
{
struct syscall_exit_args exit_args;
struct syscall *syscall;
if (pid_filter__has(&pids_filtered, getpid()))
return 0;
probe_read(&exit_args, sizeof(exit_args), args);
syscall = bpf_map_lookup_elem(&syscalls, &exit_args.syscall_nr);
if (syscall == NULL || !syscall->enabled)
return 0;
return 1;
}
license(GPL);
|
