On 27 May 2020, at 18:54, Eelco Chaudron wrote:
On 14 May 2020, at 13:56, Eelco Chaudron wrote:
On 13 May 2020, at 16:58, Eelco Chaudron wrote:
On 6 May 2020, at 3:45, Alexei Starovoitov wrote:
On Wed, Apr 29, 2020 at 4:51 AM Eelco Chaudron
<echaudro@xxxxxxxxxx> wrote:
Hi Alexie at al.
I was trying to attach a fentry/fexit trace to BPF_PROG_TYPE_EXT
BPF
program but I'm getting a verifier error, and not sure why. Is
this
supported?
<SNIP>
xdp-fexit]$ bpftool btf dump file xdpdump_bpf.o
[1] PTR '(anon)' type_id=2
[2] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64
encoding=(none)
[3] FUNC_PROTO '(anon)' ret_type_id=4 vlen=1
'ctx' type_id=1
[4] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[5] FUNC 'trace_on_exit' type_id=3
[6] STRUCT 'xdp_buff' size=48 vlen=6
'data' type_id=7 bits_offset=0
'data_end' type_id=7 bits_offset=64
'data_meta' type_id=7 bits_offset=128
'data_hard_start' type_id=7 bits_offset=192
'handle' type_id=8 bits_offset=256
'rxq' type_id=9 bits_offset=320
[7] PTR '(anon)' type_id=0
[8] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64
encoding=(none)
[9] PTR '(anon)' type_id=10
[10] STRUCT 'xdp_rxq_info' size=16 vlen=2
'dev' type_id=11 bits_offset=0
'queue_index' type_id=12 bits_offset=64
[11] PTR '(anon)' type_id=14
[12] TYPEDEF '__u32' type_id=13
[13] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32
encoding=(none)
[14] STRUCT 'net_device' size=4 vlen=1
'ifindex' type_id=4 bits_offset=0
[15] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
[16] ARRAY '(anon)' type_id=15 index_type_id=17 nr_elems=4
[17] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32
encoding=(none)
[18] VAR '_license' type_id=16, linkage=global-alloc
[19] DATASEC 'license' size=0 vlen=1
type_id=18 offset=0 size=4
Maybe you can take a quick peek why it’s failing as I have no real
experience with the verifier. I created some sample code that you can
easily use with the following instructions:
Checkout the xdp tools repo and build it:
# git clone https://github.com/chaudron/xdp-tools.git
# cd xdp-tools
# git checkout dev/xdpdump_multi
# make
# ulimit -l unlimited
# cd xdp-test
# cp ../lib/libxdp/xdp-dispatcher.o .
# ../xdp-loader/xdp-loader load -m skb eth0 test_two_bpf.o
test_bpf.o test_long_func_name.o --force
Bpftool should now show you the programs loaded, look for xdp_test_I:
# bpftool prog | grep "xdp_test_I "
199: ext name xdp_test_I tag b5a46c6e9935298c gpl
Now use the id (199) in the xdp-fexit test program
# cd ../xdp-fexit/
# git diff
- prog_fd = bpf_prog_get_fd_by_id(56);
+ prog_fd = bpf_prog_get_fd_by_id(199);
# make
Run it:
# ./fexit
- Found prog_fd = 3
- Opening object file
- Opened object file: 0xa526b0
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
func#0 @0
arg#0 type is not a struct
Unrecognized arg#0 type PTR
0: R1=ctx(id=0,off=0,imm=0) R10=fp0
; int BPF_PROG(trace_on_exit, struct xdp_buff *xdp, int ret)
0: (79) r1 = *(u64 *)(r1 +0)
invalid bpf_context access off=0 size=8
verification time 145 usec
stack depth 0
processed 1 insns (limit 1000000) max_states_per_insn 0
total_states 0 peak_states 0 mark_read 0
libbpf: -- END LOG --
libbpf: failed to load program 'fexit/xdp_test_I'
libbpf: failed to load object './xdpdump_bpf.o'
ERROR: Failed to load object file: Permission denied
Any ideas are welcome…
Hi Alexei,
I’m still trying to get attach an fentry to a EXT program, however I
did found the verifier issues…
If I attach fentry to an XDP entry point, the BPF_PROG() macro casts
the ctx to long int *, which works:
SEC("fentry/func")
int BPF_PROG(trace_on_entry, struct xdp_buff *xdp)
{
}
Is there a difference between attaching to an XDP program vs EXT that
it is requiring a struct?
So if I change my function to the below the verifier stops complaining
for the EXT program:
#define bpf_debug(fmt, ...) \
{ \
char __fmt[] = fmt; \
bpf_trace_printk(__fmt, sizeof(__fmt), \
##__VA_ARGS__); \
}
SEC("fentry/func")
int trace_on_entry(struct xdp_md *xdp)
{
bpf_debug("HALLO ID: %u", xdp->rx_queue_index);
return 0;
}
However now the verifier complains about the following and have no
clue why:
libbpf: map:xdpdump_perf_map
container_name:____btf_map_xdpdump_perf_map cannot be found in BTF.
Missing BPF_ANNOTATE_KV_PAIR?
libbpf: created map xdpdump_perf_map: fd=7
libbpf: created map xdpdump_.data: fd=8
libbpf: load_attr.prog_type 26,load_attr.attach_prog_fd 6,
load_attr.attach_btf_id 7
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
Unrecognized arg#0 type PTR
; int trace_on_entry(struct xdp_md *xdp)
0: (b7) r2 = 1965367354
; bpf_debug("HALLO ID: %u", xdp->rx_queue_index);
1: (63) *(u32 *)(r10 -8) = r2
2: (18) r2 = 0x4449204f4c4c4148
4: (7b) *(u64 *)(r10 -16) = r2
5: (b7) r2 = 0
6: (73) *(u8 *)(r10 -4) = r2
last_idx 6 first_idx 0
regs=4 stack=0 before 5: (b7) r2 = 0
7: (61) r3 = *(u32 *)(r1 +16)
func 'xdp_test_I' doesn't have 3-th argument
invalid bpf_context access off=16 size=4
processed 7 insns (limit 1000000) max_states_per_insn 0 total_states
0 peak_states 0 mark_read 0
libbpf: -- END LOG --
libbpf: failed to load program 'fentry/func'
libbpf: failed to load object './xdpdump_multi_bpf.o'
ERROR: Can't load eBPF object: Kernel verifier blocks program
loading(-4007)
This is the program details I try to attach too:
49: type 28 name xdp_test_I tag b5a46c6e9935298c gpl
loaded_at 2020-05-27T11:40:55+0000 uid 0
xlated 136B jited 108B memlock 4096B
btf_id 12
# bpftool btf dump id 12
[1] PTR '(anon)' type_id=2
[2] STRUCT 'xdp_md' size=20 vlen=5
'data' type_id=3 bits_offset=0
'data_end' type_id=3 bits_offset=32
'data_meta' type_id=3 bits_offset=64
'ingress_ifindex' type_id=3 bits_offset=96
'rx_queue_index' type_id=3 bits_offset=128
[3] TYPEDEF '__u32' type_id=4
[4] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[5] FUNC_PROTO '(anon)' ret_type_id=6 vlen=1
'ctx' type_id=1
[6] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[7] FUNC 'xdp_test_I' type_id=5 linkage=global
[8] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
[9] ARRAY '(anon)' type_id=8 index_type_id=10 nr_elems=4
[10] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32
encoding=(none)
[11] VAR '_license' type_id=9, linkage=global-alloc
[12] DATASEC 'license' size=4 vlen=1
type_id=11 offset=0 size=4
As attaching to an XDP entry point with fentry required not to use the
xdp_md struct, but the xdp_buff struct, I tried this also.
But as you can see below, also here it compliant about the xdp_test_I
function an argument (note the xdp_test_I function is the EXT function I
try to attach to).
This is the new code:
struct xdp_rxq_info {
/* Structure does not need to contain all entries,
* as "preserve_access_index" will use BTF to fix this...
*/
struct net_device *dev;
__u32 queue_index;
} __attribute__((preserve_access_index));
struct xdp_buff {
void *data;
void *data_end;
void *data_meta;
void *data_hard_start;
unsigned long handle;
struct xdp_rxq_info *rxq;
} __attribute__((preserve_access_index));
SEC("fentry/func")
int trace_on_entry(struct xdp_buff *xdp)
{
bpf_debug("HALLO ID: %u", xdp->rxq->queue_index);
return 0;
}
The result of the kernel:
libbpf: map:xdpdump_perf_map
container_name:____btf_map_xdpdump_perf_map cannot be found in BTF.
Missing BPF_ANNOTATE_KV_PAIR?
libbpf: created map xdpdump_perf_map: fd=7
libbpf: created map xdpdump_.data: fd=8
libbpf: loading kernel BTF '/sys/kernel/btf/vmlinux': 0
libbpf: prog 'fentry/func': performing 2 CO-RE offset relocs
libbpf: prog 'fentry/func': relo #0: kind 0, spec is [2] xdp_buff +
0:5 => 40.0 @ &x[0].rxq
libbpf: [2] xdp_buff: found candidate [19906] xdp_buff
libbpf: prog 'fentry/func': relo #0: matching candidate #0 xdp_buff
against spec [19906] xdp_buff + 0:4 => 32.0 @ &x[0].rxq: 1
libbpf: prog 'fentry/func': relo #0: patched insn #7 (LDX/ST/STX) off
40 -> 32
libbpf: prog 'fentry/func': relo #1: kind 0, spec is [9] xdp_rxq_info
+ 0:1 => 8.0 @ &x[0].queue_index
libbpf: [9] xdp_rxq_info: found candidate [3409] xdp_rxq_info
libbpf: prog 'fentry/func': relo #1: matching candidate #0
xdp_rxq_info against spec [3409] xdp_rxq_info + 0:1 => 8.0 @
&x[0].queue_index: 1
libbpf: prog 'fentry/func': relo #1: patched insn #8 (LDX/ST/STX) off
8 -> 8
libbpf: load_attr.prog_type 26,load_attr.attach_prog_fd 6,
load_attr.attach_btf_id 7
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
Unrecognized arg#0 type PTR
; int trace_on_entry(struct xdp_buff *xdp)
0: (b7) r2 = 1965367354
; bpf_debug("HALLO ID: %u", xdp->rxq->queue_index);
1: (63) *(u32 *)(r10 -8) = r2
2: (18) r2 = 0x4449204f4c4c4148
4: (7b) *(u64 *)(r10 -16) = r2
5: (b7) r2 = 0
6: (73) *(u8 *)(r10 -4) = r2
last_idx 6 first_idx 0
regs=4 stack=0 before 5: (b7) r2 = 0
7: (79) r1 = *(u64 *)(r1 +32)
func 'xdp_test_I' doesn't have 5-th argument
invalid bpf_context access off=32 size=8
processed 7 insns (limit 1000000) max_states_per_insn 0 total_states
0 peak_states 0 mark_read 0
libbpf: -- END LOG --
libbpf: failed to load program 'fentry/func'
libbpf: failed to load object './xdpdump_multi_bpf.o'
ERROR: Can't load eBPF object: Kernel verifier blocks program
loading(-4007)
Any input is welcome. I included the bpf list to see if others might
have any input (thought it was already).
Cheers,
Eelco
