With latest llvm17, dynptr/test_dynptr_is_null subtest failed in my testing
VM. The failure log looks like below:
All error logs:
tester_init:PASS:tester_log_buf 0 nsec
process_subtest:PASS:obj_open_mem 0 nsec
process_subtest:PASS:Can't alloc specs array 0 nsec
verify_success:PASS:dynptr_success__open 0 nsec
verify_success:PASS:bpf_object__find_program_by_name 0 nsec
verify_success:PASS:dynptr_success__load 0 nsec
verify_success:PASS:bpf_program__attach 0 nsec
verify_success:FAIL:err unexpected err: actual 4 != expected 0
#65/9 dynptr/test_dynptr_is_null:FAIL
The error happens for bpf prog test_dynptr_is_null in dynptr_success.c:
if (bpf_dynptr_is_null(&ptr2)) {
err = 4;
goto exit;
}
The bpf_dynptr_is_null(&ptr) unexpectedly returned a non-zero value and
the control went to the error path. Digging further, I found the root cause
is due to function signature difference between kernel and user space.
In kernel, we have ...
__bpf_kfunc bool bpf_dynptr_is_null(struct bpf_dynptr_kern *ptr)
... while in bpf_kfuncs.h we have:
extern int bpf_dynptr_is_null(const struct bpf_dynptr *ptr) __ksym;
The kernel bpf_dynptr_is_null disasm code:
ffffffff812f1a90 <bpf_dynptr_is_null>:
ffffffff812f1a90: f3 0f 1e fa endbr64
ffffffff812f1a94: 0f 1f 44 00 00 nopl (%rax,%rax)
ffffffff812f1a99: 53 pushq %rbx
ffffffff812f1a9a: 48 89 fb movq %rdi, %rbx
ffffffff812f1a9d: e8 ae 29 17 00 callq 0xffffffff81464450 <__asan_load8_noabort>
ffffffff812f1aa2: 48 83 3b 00 cmpq $0x0, (%rbx)
ffffffff812f1aa6: 0f 94 c0 sete %al
ffffffff812f1aa9: 5b popq %rbx
ffffffff812f1aaa: c3 retq
Note that only 1-byte register %al is set and the other 7-bytes are not
touched. In bpf program, the asm code for the above bpf_dynptr_is_null(&ptr2):
266: 85 10 00 00 ff ff ff ff call -0x1
267: b4 01 00 00 04 00 00 00 w1 = 0x4
268: 16 00 03 00 00 00 00 00 if w0 == 0x0 goto +0x3 <LBB9_8>
Basically, 4-byte subregister is tested. This might cause error as the value
other than the lowest byte might not be 0.
This patch fixed the issue by using the identical func prototype across kernel
and selftest user space. The fixed bpf asm code:
267: 85 10 00 00 ff ff ff ff call -0x1
268: 54 00 00 00 01 00 00 00 w0 &= 0x1
269: b4 01 00 00 04 00 00 00 w1 = 0x4
270: 16 00 03 00 00 00 00 00 if w0 == 0x0 goto +0x3 <LBB9_8>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230517040404.4023912-1-yhs@fb.com
Once we enable -Wall for BPF sources, compiler will complain about lots
of unused variables, variables that are set but never read, etc.
Fix all these issues first before enabling -Wall in Makefile.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230309054015.4068562-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Test skb and xdp dynptr functionality in the following ways:
1) progs/test_cls_redirect_dynptr.c
* Rewrite "progs/test_cls_redirect.c" test to use dynptrs to parse
skb data
* This is a great example of how dynptrs can be used to simplify a
lot of the parsing logic for non-statically known values.
When measuring the user + system time between the original version
vs. using dynptrs, and averaging the time for 10 runs (using
"time ./test_progs -t cls_redirect"):
original version: 0.092 sec
with dynptrs: 0.078 sec
2) progs/test_xdp_dynptr.c
* Rewrite "progs/test_xdp.c" test to use dynptrs to parse xdp data
When measuring the user + system time between the original version
vs. using dynptrs, and averaging the time for 10 runs (using
"time ./test_progs -t xdp_attach"):
original version: 0.118 sec
with dynptrs: 0.094 sec
3) progs/test_l4lb_noinline_dynptr.c
* Rewrite "progs/test_l4lb_noinline.c" test to use dynptrs to parse
skb data
When measuring the user + system time between the original version
vs. using dynptrs, and averaging the time for 10 runs (using
"time ./test_progs -t l4lb_all"):
original version: 0.062 sec
with dynptrs: 0.081 sec
For number of processed verifier instructions:
original version: 6268 insns
with dynptrs: 2588 insns
4) progs/test_parse_tcp_hdr_opt_dynptr.c
* Add sample code for parsing tcp hdr opt lookup using dynptrs.
This logic is lifted from a real-world use case of packet parsing
in katran [0], a layer 4 load balancer. The original version
"progs/test_parse_tcp_hdr_opt.c" (not using dynptrs) is included
here as well, for comparison.
When measuring the user + system time between the original version
vs. using dynptrs, and averaging the time for 10 runs (using
"time ./test_progs -t parse_tcp_hdr_opt"):
original version: 0.031 sec
with dynptrs: 0.045 sec
5) progs/dynptr_success.c
* Add test case "test_skb_readonly" for testing attempts at writes
on a prog type with read-only skb ctx.
* Add "test_dynptr_skb_data" for testing that bpf_dynptr_data isn't
supported for skb progs.
6) progs/dynptr_fail.c
* Add test cases "skb_invalid_data_slice{1,2,3,4}" and
"xdp_invalid_data_slice{1,2}" for testing that helpers that modify the
underlying packet buffer automatically invalidate the associated
data slice.
* Add test cases "skb_invalid_ctx" and "xdp_invalid_ctx" for testing
that prog types that do not support bpf_dynptr_from_skb/xdp don't
have access to the API.
* Add test case "dynptr_slice_var_len{1,2}" for testing that
variable-sized len can't be passed in to bpf_dynptr_slice
* Add test case "skb_invalid_slice_write" for testing that writes to a
read-only data slice are rejected by the verifier.
* Add test case "data_slice_out_of_bounds_skb" for testing that
writes to an area outside the slice are rejected.
* Add test case "invalid_slice_rdwr_rdonly" for testing that prog
types that don't allow writes to packet data don't accept any calls
to bpf_dynptr_slice_rdwr.
[0] https://github.com/facebookincubator/katran/blob/main/katran/lib/bpf/pckt_parsing.h
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230301154953.641654-11-joannelkoong@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
