From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, Martin KaFai Lau <kafai@fb.com>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Peter Zijlstra <peterz@infradead.org>,
"Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Subject: Re: [PATCHv2 bpf-next 2/6] ftrace: Keep the resolved addr in kallsyms_callback
Date: Thu, 8 Sep 2022 21:35:51 +0900 [thread overview]
Message-ID: <20220908213551.5d51406ff9846bcd079fcc3f@kernel.org> (raw)
In-Reply-To: <20220811091526.172610-3-jolsa@kernel.org>
On Thu, 11 Aug 2022 11:15:22 +0200
Jiri Olsa <jolsa@kernel.org> wrote:
> Keeping the resolved 'addr' in kallsyms_callback, instead of taking
> ftrace_location value, because we depend on symbol address in the
> cookie related code.
>
> With CONFIG_X86_KERNEL_IBT option the ftrace_location value differs
> from symbol address, which screwes the symbol address cookies matching.
>
> There are 2 users of this function:
> - bpf_kprobe_multi_link_attach
> for which this fix is for
>
> - get_ftrace_locations
> which is used by register_fprobe_syms
>
> this function needs to get symbols resolved to addresses,
> but does not need 'ftrace location addresses' at this point
> there's another ftrace location translation in the path done
> by ftrace_set_filter_ips call:
>
> register_fprobe_syms
> addrs = get_ftrace_locations
>
> register_fprobe_ips(addrs)
> ...
> ftrace_set_filter_ips
> ...
> __ftrace_match_addr
> ip = ftrace_location(ip);
> ...
>
Yes, this looks OK for fprobe. I confirmed above.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
One concern was that the caller might expect that the address
must be ftrace_location(), but as far as I can read the function
document, there is no such description.
* ftrace_lookup_symbols - Lookup addresses for array of symbols
...
* This function looks up addresses for array of symbols provided in
* @syms array (must be alphabetically sorted) and stores them in
* @addrs array, which needs to be big enough to store at least @cnt
* addresses.
So this change is OK.
Thank you,
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> kernel/trace/ftrace.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index bc921a3f7ea8..8a8c90d1a387 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -8268,8 +8268,7 @@ static int kallsyms_callback(void *data, const char *name,
> if (args->addrs[idx])
> return 0;
>
> - addr = ftrace_location(addr);
> - if (!addr)
> + if (!ftrace_location(addr))
> return 0;
>
> args->addrs[idx] = addr;
> --
> 2.37.1
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
next prev parent reply other threads:[~2022-09-08 12:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-11 9:15 [PATCHv2 bpf-next 0/6] bpf: Fixes for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 1/6] kprobes: Add new KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag Jiri Olsa
2022-08-15 9:57 ` Peter Zijlstra
2022-08-15 10:10 ` Jiri Olsa
2022-08-15 12:40 ` Peter Zijlstra
2022-08-16 7:01 ` Jiri Olsa
2022-08-30 15:08 ` Jiri Olsa
2022-09-08 8:26 ` Jiri Olsa
2022-09-08 12:01 ` Masami Hiramatsu
2022-08-11 9:15 ` [PATCHv2 bpf-next 2/6] ftrace: Keep the resolved addr in kallsyms_callback Jiri Olsa
2022-08-15 10:13 ` Peter Zijlstra
2022-08-15 10:30 ` Jiri Olsa
2022-08-15 12:45 ` Peter Zijlstra
2022-08-16 7:06 ` Jiri Olsa
2022-09-08 12:35 ` Masami Hiramatsu [this message]
2022-09-08 19:41 ` Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 3/6] bpf: Use given function address for trampoline ip arg Jiri Olsa
2022-08-15 10:18 ` Peter Zijlstra
2022-08-15 10:57 ` Jiri Olsa
2022-08-15 12:51 ` Peter Zijlstra
2022-08-17 13:40 ` Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 4/6] bpf: Adjust kprobe_multi entry_ip for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 5/6] bpf: Return value in kprobe get_func_ip only for entry address Jiri Olsa
2022-08-11 9:15 ` [PATCHv2 bpf-next 6/6] selftests/bpf: Fix get_func_ip offset test for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-08-16 3:25 ` Andrii Nakryiko
2022-08-16 7:00 ` Jiri Olsa
2022-08-16 10:18 ` Jiri Olsa
2022-08-16 17:28 ` Andrii Nakryiko
2022-08-16 17:19 ` Andrii Nakryiko
2022-08-16 3:27 ` [PATCHv2 bpf-next 0/6] bpf: Fixes " Andrii Nakryiko
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