netdev - Re: [PATCH bpf-next 1/4] samples: bpf: fix bpf programs with kprobe/sys

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Message-ID: <c4061b5f-b42e-4ecc-e3fb-7a70206da417@fb.com>
Date:   Wed, 1 Jul 2020 22:12:58 -0700
From:   Yonghong Song <yhs@...com>
To:     "Daniel T. Lee" <danieltimlee@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Andrii Nakryiko <andriin@...com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/4] samples: bpf: fix bpf programs with
 kprobe/sys_connect event



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))

> 
> 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 = {};
>