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Message-ID: <41ca5ad1-2b79-dbc2-5f6e-e466712fe7a9@fb.com>
Date: Thu, 2 Jul 2020 09:04:19 -0700
From: Yonghong Song <yhs@...com>
To: "Daniel T. Lee" <danieltimlee@...il.com>
CC: Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Andrii Nakryiko <andriin@...com>,
netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/4] samples: bpf: fix bpf programs with
kprobe/sys_connect event
On 7/2/20 4:13 AM, Daniel T. Lee wrote:
> On Thu, Jul 2, 2020 at 2:13 PM Yonghong Song <yhs@...com> wrote:
>>
>>
>>
>> On 7/1/20 7:16 PM, Daniel T. Lee wrote:
>>> Currently, BPF programs with kprobe/sys_connect does not work properly.
>>>
>>> Commit 34745aed515c ("samples/bpf: fix kprobe attachment issue on x64")
>>> This commit modifies the bpf_load behavior of kprobe events in the x64
>>> architecture. If the current kprobe event target starts with "sys_*",
>>> add the prefix "__x64_" to the front of the event.
>>>
>>> Appending "__x64_" prefix with kprobe/sys_* event was appropriate as a
>>> solution to most of the problems caused by the commit below.
>>>
>>> commit d5a00528b58c ("syscalls/core, syscalls/x86: Rename struct
>>> pt_regs-based sys_*() to __x64_sys_*()")
>>>
>>> However, there is a problem with the sys_connect kprobe event that does
>>> not work properly. For __sys_connect event, parameters can be fetched
>>> normally, but for __x64_sys_connect, parameters cannot be fetched.
>>>
>>> Because of this problem, this commit fixes the sys_connect event by
>>> specifying the __sys_connect directly and this will bypass the
>>> "__x64_" appending rule of bpf_load.
>>
>> In the kernel code, we have
>>
>> SYSCALL_DEFINE3(connect, int, fd, struct sockaddr __user *, uservaddr,
>> int, addrlen)
>> {
>> return __sys_connect(fd, uservaddr, addrlen);
>> }
>>
>> Depending on compiler, there is no guarantee that __sys_connect will
>> not be inlined. I would prefer to still use the entry point
>> __x64_sys_* e.g.,
>> SEC("kprobe/" SYSCALL(sys_write))
>>
>
> As you mentioned, there is clearly a possibility that problems may arise
> because the symbol does not exist according to the compiler.
>
> However, in x64, when using Kprobe for __x64_sys_connect event, the
> tests are not working properly because the parameters cannot be fetched,
> and the test under selftests/bpf is using "kprobe/_sys_connect" directly.
This is the assembly code for __x64_sys_connect.
ffffffff818d3520 <__x64_sys_connect>:
ffffffff818d3520: e8 fb df 32 00 callq 0xffffffff81c01520
<__fentry__>
ffffffff818d3525: 48 8b 57 60 movq 96(%rdi), %rdx
ffffffff818d3529: 48 8b 77 68 movq 104(%rdi), %rsi
ffffffff818d352d: 48 8b 7f 70 movq 112(%rdi), %rdi
ffffffff818d3531: e8 1a ff ff ff callq 0xffffffff818d3450
<__sys_connect>
ffffffff818d3536: 48 98 cltq
ffffffff818d3538: c3 retq
ffffffff818d3539: 0f 1f 80 00 00 00 00 nopl (%rax)
In bpf program, the step is:
struct pt_regs *real_regs = PT_REGS_PARM1(pt_regs);
param1 = PT_REGS_PARM1(real_regs);
param2 = PT_REGS_PARM2(real_regs);
param3 = PT_REGS_PARM3(real_regs);
The same for s390.
For other architectures, no above indirection is needed.
I guess you can abstract the above into trace_common.h?
>
> I'm not sure how to deal with this problem. Any advice and suggestions
> will be greatly appreciated.
>
> Thanks for your time and effort for the review.
> Daniel
>
>>>
>>> Fixes: 34745aed515c ("samples/bpf: fix kprobe attachment issue on x64")
>>> Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
>>> ---
>>> samples/bpf/map_perf_test_kern.c | 2 +-
>>> samples/bpf/test_map_in_map_kern.c | 2 +-
>>> samples/bpf/test_probe_write_user_kern.c | 2 +-
>>> 3 files changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/samples/bpf/map_perf_test_kern.c b/samples/bpf/map_perf_test_kern.c
>>> index 12e91ae64d4d..cebe2098bb24 100644
>>> --- a/samples/bpf/map_perf_test_kern.c
>>> +++ b/samples/bpf/map_perf_test_kern.c
>>> @@ -154,7 +154,7 @@ int stress_percpu_hmap_alloc(struct pt_regs *ctx)
>>> return 0;
>>> }
>>>
>>> -SEC("kprobe/sys_connect")
>>> +SEC("kprobe/__sys_connect")
>>> int stress_lru_hmap_alloc(struct pt_regs *ctx)
>>> {
>>> char fmt[] = "Failed at stress_lru_hmap_alloc. ret:%dn";
>>> diff --git a/samples/bpf/test_map_in_map_kern.c b/samples/bpf/test_map_in_map_kern.c
>>> index 6cee61e8ce9b..b1562ba2f025 100644
>>> --- a/samples/bpf/test_map_in_map_kern.c
>>> +++ b/samples/bpf/test_map_in_map_kern.c
>>> @@ -102,7 +102,7 @@ static __always_inline int do_inline_hash_lookup(void *inner_map, u32 port)
>>> return result ? *result : -ENOENT;
>>> }
>>>
>>> -SEC("kprobe/sys_connect")
>>> +SEC("kprobe/__sys_connect")
>>> int trace_sys_connect(struct pt_regs *ctx)
>>> {
>>> struct sockaddr_in6 *in6;
>>> diff --git a/samples/bpf/test_probe_write_user_kern.c b/samples/bpf/test_probe_write_user_kern.c
>>> index 6579639a83b2..9b3c3918c37d 100644
>>> --- a/samples/bpf/test_probe_write_user_kern.c
>>> +++ b/samples/bpf/test_probe_write_user_kern.c
>>> @@ -26,7 +26,7 @@ struct {
>>> * This example sits on a syscall, and the syscall ABI is relatively stable
>>> * of course, across platforms, and over time, the ABI may change.
>>> */
>>> -SEC("kprobe/sys_connect")
>>> +SEC("kprobe/__sys_connect")
>>> int bpf_prog1(struct pt_regs *ctx)
>>> {
>>> struct sockaddr_in new_addr, orig_addr = {};
>>>
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