On 4 Dec 2019, at 19:52, Eelco Chaudron wrote:
On 4 Dec 2019, at 19:01, Yonghong Song wrote:
<SNIP>
I’ve put my code on GitHub, maybe it’s just something stupid…
Thanks for the test case. This indeed a kernel bug.
The following change fixed the issue:
-bash-4.4$ git diff
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a0482e1c4a77..034ef81f935b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9636,7 +9636,10 @@ static int check_attach_btf_id(struct
bpf_verifier_env *env)
ret = -EINVAL;
goto out;
}
- addr = (long)
tgt_prog->aux->func[subprog]->bpf_func;
+ if (subprog == 0)
+ addr = (long) tgt_prog->bpf_func;
+ else
+ addr = (long)
tgt_prog->aux->func[subprog]->bpf_func;
} else {
addr = kallsyms_lookup_name(tname);
if (!addr) {
-bash-4.4$
The reason is for a bpf program without any additional subprogram
(callees), tgt_prog->aux->func is not populated and is a NULL
pointer,
so the access tgt_prog->aux->func[0]->bpf_func will segfault.
With the above change, your test works properly.
Thanks for the quick response, and as you mention the test passes with
the patch above.
I will continue my experiments later this week, and let you know if I
run into any other problems.
With the following program I get some access errors:
#define bpf_debug(fmt, ...) \
{ \
char __fmt[] = fmt; \
bpf_trace_printk(__fmt, sizeof(__fmt), \
##__VA_ARGS__); \
}
BPF_TRACE_2("fexit/xdp_prog_simple", trace_on_exit,
struct xdp_md *, xdp, int, ret)
{
__u32 rx_queue;
__builtin_preserve_access_index(({
rx_queue = xdp->rx_queue_index;
}));
bpf_debug("fexit: queue = %u, ret = %d\n", rx_queue, ret);
return 0;
}
I assume the XDP context has not been vetted?
libbpf: -- BEGIN DUMP LOG ---
libbpf:
func#0 @0
BPF program ctx type is not a struct
Type info disagrees with actual arguments due to compiler optimizations
0: R1=ctx(id=0,off=0,imm=0) R10=fp0
; BPF_TRACE_2("fexit/xdp_prog_simple", trace_on_exit,
0: (b7) r2 = 16
1: R1=ctx(id=0,off=0,imm=0) R2_w=inv16 R10=fp0
; BPF_TRACE_2("fexit/xdp_prog_simple", trace_on_exit,
1: (79) r3 = *(u64 *)(r1 +0)
2: R1=ctx(id=0,off=0,imm=0) R2_w=inv16
R3_w=ptr_xdp_buff(id=0,off=0,imm=0) R10=fp0
2: (0f) r3 += r2
last_idx 2 first_idx 0
regs=4 stack=0 before 1: (79) r3 = *(u64 *)(r1 +0)
regs=4 stack=0 before 0: (b7) r2 = 16
3: R1=ctx(id=0,off=0,imm=0) R2_w=invP16
R3_w=ptr_xdp_buff(id=0,off=16,imm=0) R10=fp0
; rx_queue = xdp->rx_queue_index;
3: (61) r3 = *(u32 *)(r3 +0)
cannot access ptr member data_meta with moff 16 in struct xdp_buff with
off 16 size 4
verification time 102 usec
stack depth 0
processed 4 insns (limit 1000000) max_states_per_insn 0 total_states 0
peak_states 0 mark_read 0
libbpf: -- END LOG --
Trying to use the helpers, passes verification, however, it’s dumping
invalid content:
BPF_TRACE_2("fexit/xdp_prog_simple", trace_on_exit,
struct xdp_md *, xdp, int, ret)
{
__u32 rx_queue;
bpf_probe_read_kernel(&rx_queue, sizeof(rx_queue),
__builtin_preserve_access_index(&xdp->rx_queue_index));
bpf_debug("fexit: queue = %u, ret = %d\n", rx_queue, ret);
return 0;
}
Debug output:
ping6-2752 [004] ..s1 60763.917790: 0: SIMPLE: [ifindex = 4, queue
= 0]
ping6-2752 [004] ..s1 60763.917800: 0: fexit: queue = 2969379072,
ret = 2
ping6-2752 [004] ..s1 60764.941817: 0: SIMPLE: [ifindex = 4, queue
= 0]
ping6-2752 [004] ..s1 60764.941828: 0: fexit: queue = 2969379072,
ret = 2
ping6-2752 [004] ..s1 60765.965835: 0: SIMPLE: [ifindex = 4, queue
= 0]
Tried the same with fentry for this function, but the same results as
fexit.
Any hints?
Thanks,
Eelco
