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Date: Thu, 1 Nov 2018 15:52:17 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Yonghong Song <yhs@...com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
Jiri Olsa <jolsa@...hat.com>, Martin Lau <kafai@...com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Linux Networking Development Mailing List
<netdev@...r.kernel.org>
Subject: Help with the BPF verifier
tl;dr: I seem to be trying to get past clang optimizations that get the
verifier to accept my proggie.
Hi,
So I'm moving to use raw_syscalls:sys_exit to collect pointer
contents, using maps to tell the bpf program what to copy, how many
bytes, filters, etc.
I'm at the start of it at this point I need to use an index to
get to the right syscall arg that is a filename, starting just with
"open" and "openat", that have the filename in different args, so to get
this first part working I'm doing it directly in the bpf restricted C
program, later this will be to maps, etc, so if I set the index as a
constant, just for testing, it works, look at the "open" and "openat"
calls below, later we'll see why openat is failing to augment its
"filename" arg while "open" works:
[root@...enth perf]# trace -e tools/perf/examples/bpf/augmented_raw_syscalls.c sleep 1
? ( ): sleep/10152 ... [continued]: execve()) = 0
0.045 ( 0.004 ms): sleep/10152 brk() = 0x55ccff356000
0.074 ( 0.007 ms): sleep/10152 access(filename: , mode: R) = -1 ENOENT No such file or directory
0.089 ( 0.006 ms): sleep/10152 openat(dfd: CWD, filename: , flags: CLOEXEC) = 3
0.097 ( 0.003 ms): sleep/10152 fstat(fd: 3, statbuf: 0x7ffecdd283f0) = 0
0.103 ( 0.006 ms): sleep/10152 mmap(len: 103334, prot: READ, flags: PRIVATE, fd: 3) = 0x7f8ffee9c000
0.111 ( 0.002 ms): sleep/10152 close(fd: 3) = 0
0.135 ( 0.007 ms): sleep/10152 openat(dfd: CWD, filename: , flags: CLOEXEC) = 3
0.144 ( 0.003 ms): sleep/10152 read(fd: 3, buf: 0x7ffecdd285b8, count: 832) = 832
0.150 ( 0.002 ms): sleep/10152 fstat(fd: 3, statbuf: 0x7ffecdd28450) = 0
0.155 ( 0.005 ms): sleep/10152 mmap(len: 8192, prot: READ|WRITE, flags: PRIVATE|ANONYMOUS) = 0x7f8ffee9a000
0.166 ( 0.007 ms): sleep/10152 mmap(len: 3889792, prot: EXEC|READ, flags: PRIVATE|DENYWRITE, fd: 3) = 0x7f8ffe8dc000
0.175 ( 0.010 ms): sleep/10152 mprotect(start: 0x7f8ffea89000, len: 2093056) = 0
0.188 ( 0.010 ms): sleep/10152 mmap(addr: 0x7f8ffec88000, len: 24576, prot: READ|WRITE, flags: PRIVATE|FIXED|DENYWRITE, fd: 3, off: 1753088) = 0x7f8ffec88000
0.204 ( 0.005 ms): sleep/10152 mmap(addr: 0x7f8ffec8e000, len: 14976, prot: READ|WRITE, flags: PRIVATE|FIXED|ANONYMOUS) = 0x7f8ffec8e000
0.218 ( 0.002 ms): sleep/10152 close(fd: 3) = 0
0.239 ( 0.002 ms): sleep/10152 arch_prctl(option: 4098, arg2: 140256433779968) = 0
0.312 ( 0.009 ms): sleep/10152 mprotect(start: 0x7f8ffec88000, len: 16384, prot: READ) = 0
0.343 ( 0.005 ms): sleep/10152 mprotect(start: 0x55ccff1c6000, len: 4096, prot: READ) = 0
0.354 ( 0.006 ms): sleep/10152 mprotect(start: 0x7f8ffeeb6000, len: 4096, prot: READ) = 0
0.362 ( 0.019 ms): sleep/10152 munmap(addr: 0x7f8ffee9c000, len: 103334) = 0
0.476 ( 0.002 ms): sleep/10152 brk() = 0x55ccff356000
0.480 ( 0.004 ms): sleep/10152 brk(brk: 0x55ccff377000) = 0x55ccff377000
0.487 ( 0.002 ms): sleep/10152 brk() = 0x55ccff377000
0.497 ( 0.008 ms): sleep/10152 open(filename: /usr/lib/locale/locale-archive, flags: CLOEXEC) = 3
0.507 ( 0.002 ms): sleep/10152 fstat(fd: 3, statbuf: 0x7f8ffec8daa0) = 0
0.511 ( 0.006 ms): sleep/10152 mmap(len: 113045344, prot: READ, flags: PRIVATE, fd: 3) = 0x7f8ff7d0d000
0.524 ( 0.002 ms): sleep/10152 close(fd: 3) = 0
0.574 (1000.140 ms): sleep/10152 nanosleep(rqtp: 0x7ffecdd29130) = 0
1000.753 ( 0.007 ms): sleep/10152 close(fd: 1) = 0
1000.767 ( 0.004 ms): sleep/10152 close(fd: 2) = 0
1000.781 ( ): sleep/10152 exit_group()
[root@...enth perf]#
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Augment the raw_syscalls tracepoints with the contents of the pointer arguments.
4 *
5 * Test it with:
6 *
7 * perf trace -e tools/perf/examples/bpf/augmented_raw_syscalls.c cat /etc/passwd > /dev/null
8 *
9 * This exactly matches what is marshalled into the raw_syscall:sys_enter
10 * payload expected by the 'perf trace' beautifiers.
11 *
12 * For now it just uses the existing tracepoint augmentation code in 'perf
13 * trace', in the next csets we'll hook up these with the sys_enter/sys_exit
14 * code that will combine entry/exit in a strace like way.
15 */
16 #include <stdio.h>
17 #include <linux/socket.h>
18 /* bpf-output associated map */
19 struct bpf_map SEC("maps") __augmented_syscalls__ = {
20 .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
21 .key_size = sizeof(int),
22 .value_size = sizeof(u32),
23 .max_entries = __NR_CPUS__,
24 };
25 struct syscall_enter_args {
26 unsigned long long common_tp_fields;
27 long syscall_nr;
28 unsigned long args[6];
29 };
30 struct syscall_exit_args {
31 unsigned long long common_tp_fields;
32 long syscall_nr;
33 long ret;
34 };
35 struct augmented_filename {
36 unsigned int size;
37 int reserved;
38 char value[256];
39 };
40 #define SYS_OPEN 2
41 #define SYS_OPENAT 257
42 SEC("raw_syscalls:sys_enter")
43 int sys_enter(struct syscall_enter_args *args)
44 {
45 struct {
46 struct syscall_enter_args args;
47 struct augmented_filename filename;
48 } augmented_args;
49 unsigned int len = sizeof(augmented_args);
50 unsigned int filename_arg = 6;
51 probe_read(&augmented_args.args, sizeof(augmented_args.args), args);
52 switch (augmented_args.args.syscall_nr) {
53 case SYS_OPEN: filename_arg = 0; break;
54 case SYS_OPENAT: filename_arg = 1; break;
55 }
56 if (filename_arg <= 5) {
57 augmented_args.filename.reserved = 0;
58 augmented_args.filename.size = probe_read_str(&augmented_args.filename.value,
59 sizeof(augmented_args.filename.value),
60 (const void *)args->args[0]);
61 if (augmented_args.filename.size < sizeof(augmented_args.filename.value)) {
62 len -= sizeof(augmented_args.filename.value) - augmented_args.filename.size;
63 len &= sizeof(augmented_args.filename.value) - 1;
64 }
65 } else {
66 len = sizeof(augmented_args.args);
67 }
68 perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, &augmented_args, len);
69 return 0;
70 }
71 SEC("raw_syscalls:sys_exit")
72 int sys_exit(struct syscall_exit_args *args)
73 {
74 return 1; /* 0 as soon as we start copying data returned by the kernel, e.g. 'read' */
75 }
76 license(GPL);
In line #60 if I change that to 1, then "openat" works and "open"
doesn't, so what I wanted was to use filename_arg there as the index,
now it comes from that switch, but really it'll come from userspace,
that knows the syscall tables for each arch, etc.
But if I do that, i.e. apply this patch to that program:
--- /wb/augmented_raw_syscalls.c.old 2018-11-01 15:43:55.000394234 -0300
+++ /wb/augmented_raw_syscalls.c 2018-11-01 15:44:15.102367838 -0300
@@ -67,7 +67,7 @@
augmented_args.filename.reserved = 0;
augmented_args.filename.size = probe_read_str(&augmented_args.filename.value,
sizeof(augmented_args.filename.value),
- (const void *)args->args[0]);
+ (const void *)args->args[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;
Then I end up with the verifier complying, I tried various ways to get
around the compiler about filename_arg being safe to use as an index,
but I couldn't find the right trick, ideas?
This is what I end up with when I apply that patch:
[root@...enth perf]# trace -e tools/perf/examples/bpf/augmented_raw_syscalls.c sleep 1
event syntax error: 'tools/perf/examples/bpf/augmented_raw_syscalls.c'
\___ Kernel verifier blocks program loading
(add -v to see detail)
Run 'perf list' for a list of valid events
Usage: perf trace [<options>] [<command>]
or: perf trace [<options>] -- <command> [<options>]
or: perf trace record [<options>] [<command>]
or: perf trace record [<options>] -- <command> [<options>]
-e, --event <event> event/syscall selector. use 'perf list' to list available events
[root@...enth perf]#
Using -v, as suggested, I get:
[root@...enth perf]# trace -v -e tools/perf/examples/bpf/augmented_raw_syscalls.c sleep 1
bpf: builtin compilation failed: -95, try external compiler
Kernel build dir is set to /lib/modules/4.19.0-rc8-00014-gc0cff31be705/build
set env: KBUILD_DIR=/lib/modules/4.19.0-rc8-00014-gc0cff31be705/build
unset env: KBUILD_OPTS
include option is set to -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h
set env: NR_CPUS=4
set env: LINUX_VERSION_CODE=0x41300
set env: CLANG_EXEC=/usr/local/bin/clang
unset env: CLANG_OPTIONS
set env: KERNEL_INC_OPTIONS= -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h
set env: PERF_BPF_INC_OPTIONS=-I/home/acme/lib/perf/include/bpf
set env: WORKING_DIR=/lib/modules/4.19.0-rc8-00014-gc0cff31be705/build
set env: CLANG_SOURCE=/home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c
llvm compiling command template: $CLANG_EXEC -D__KERNEL__ -D__NR_CPUS__=$NR_CPUS -DLINUX_VERSION_CODE=$LINUX_VERSION_CODE $CLANG_OPTIONS $PERF_BPF_INC_OPTIONS $KERNEL_INC_OPTIONS -Wno-unused-value -Wno-pointer-sign -working-directory $WORKING_DIR -c "$CLANG_SOURCE" -target bpf $CLANG_EMIT_LLVM -O2 -o - $LLVM_OPTIONS_PIPE
llvm compiling command : /usr/local/bin/clang -D__KERNEL__ -D__NR_CPUS__=4 -DLINUX_VERSION_CODE=0x41300 -I/home/acme/lib/perf/include/bpf -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated -I/home/acme/git/linux/include -I./include -I/home/acme/git/linux/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi -I./include/generated/uapi -include /home/acme/git/linux/include/linux/kconfig.h -Wno-unused-value -Wno-pointer-sign -working-directory /lib/modules/4.19.0-rc8-00014-gc0cff31be705/build -c /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c -target bpf -O2 -o -
libbpf: loading object 'tools/perf/examples/bpf/augmented_raw_syscalls.c' from buffer
libbpf: section(1) .strtab, size 168, link 0, flags 0, type=3
libbpf: skip section(1) .strtab
libbpf: section(2) .text, size 0, link 0, flags 6, type=1
libbpf: skip section(2) .text
libbpf: section(3) raw_syscalls:sys_enter, size 376, link 0, flags 6, type=1
libbpf: found program raw_syscalls:sys_enter
libbpf: section(4) .relraw_syscalls:sys_enter, size 16, link 10, flags 0, type=9
libbpf: section(5) raw_syscalls:sys_exit, size 16, link 0, flags 6, type=1
libbpf: found program raw_syscalls:sys_exit
libbpf: section(6) maps, size 56, link 0, flags 3, type=1
libbpf: section(7) license, size 4, link 0, flags 3, type=1
libbpf: license of tools/perf/examples/bpf/augmented_raw_syscalls.c is GPL
libbpf: section(8) version, size 4, link 0, flags 3, type=1
libbpf: kernel version of tools/perf/examples/bpf/augmented_raw_syscalls.c is 41300
libbpf: section(9) .llvm_addrsig, size 6, link 10, flags 80000000, type=1879002115
libbpf: skip section(9) .llvm_addrsig
libbpf: section(10) .symtab, size 240, link 1, flags 0, type=2
libbpf: maps in tools/perf/examples/bpf/augmented_raw_syscalls.c: 2 maps in 56 bytes
libbpf: map 0 is "__augmented_syscalls__"
libbpf: map 1 is "__bpf_stdout__"
libbpf: collecting relocating info for: 'raw_syscalls:sys_enter'
libbpf: relo for 4 value 28 name 124
libbpf: relocation: insn_idx=39
libbpf: relocation: find map 1 (__augmented_syscalls__) for insn 39
bpf: config program 'raw_syscalls:sys_enter'
bpf: config program 'raw_syscalls:sys_exit'
libbpf: create map __bpf_stdout__: fd=3
libbpf: create map __augmented_syscalls__: fd=4
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
0: (bf) r6 = r1
1: (bf) r1 = r10
2: (07) r1 += -328
3: (b7) r7 = 64
4: (b7) r2 = 64
5: (bf) r3 = r6
6: (85) call bpf_probe_read#4
7: (b7) r2 = 1
8: (79) r3 = *(u64 *)(r10 -320)
9: (15) if r3 == 0x101 goto pc+1
R0=inv(id=0) R2=inv1 R3=inv(id=0) R6=ctx(id=0,off=0,imm=0) R7=inv64 R10=fp0,call_-1
10: (b7) r2 = 6
11: (b7) r1 = 0
12: (15) if r3 == 0x2 goto pc+1
R0=inv(id=0) R1=inv0 R2=inv6 R3=inv(id=0) R6=ctx(id=0,off=0,imm=0) R7=inv64 R10=fp0,call_-1
13: (bf) r1 = r2
14: (25) if r1 > 0x5 goto pc+21
R0=inv(id=0) R1=inv6 R2=inv6 R3=inv(id=0) R6=ctx(id=0,off=0,imm=0) R7=inv64 R10=fp0,call_-1
15: (b7) r2 = 0
16: (63) *(u32 *)(r10 -260) = r2
17: (67) r1 <<= 32
18: (77) r1 >>= 32
19: (67) r1 <<= 3
20: (bf) r2 = r6
21: (0f) r2 += r1
22: (79) r3 = *(u64 *)(r2 +16)
R2 invalid mem access 'inv'
libbpf: -- END LOG --
libbpf: failed to load program 'raw_syscalls:sys_enter'
libbpf: failed to load object 'tools/perf/examples/bpf/augmented_raw_syscalls.c'
bpf: load objects failed: err=-4007: (Kernel verifier blocks program loading)
event syntax error: 'tools/perf/examples/bpf/augmented_raw_syscalls.c'
\___ Kernel verifier blocks program loading
(add -v to see detail)
Run 'perf list' for a list of valid events
Usage: perf trace [<options>] [<command>]
or: perf trace [<options>] -- <command> [<options>]
or: perf trace record [<options>] [<command>]
or: perf trace record [<options>] -- <command> [<options>]
-e, --event <event> event/syscall selector. use 'perf list' to list available events
[root@...enth perf]#
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