From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martynas Pumputis <m@lambda.lt>,
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>,
"Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Subject: Re: [PATCHv3 bpf-next 4/6] bpf: Adjust kprobe_multi entry_ip for CONFIG_X86_KERNEL_IBT
Date: Fri, 9 Sep 2022 13:49:16 +0200 [thread overview]
Message-ID: <YxsoPLVnSjcTqQDf@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20220909101245.347173-5-jolsa@kernel.org>
On Fri, Sep 09, 2022 at 12:12:43PM +0200, Jiri Olsa wrote:
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 68e5cdd24cef..bcada91b0b3b 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2419,6 +2419,10 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
> {
> struct bpf_kprobe_multi_link *link;
>
> +#ifdef CONFIG_X86_KERNEL_IBT
> + if (is_endbr(*((u32 *) entry_ip - 1)))
> + entry_ip -= ENDBR_INSN_SIZE;
> +#endif
> link = container_of(fp, struct bpf_kprobe_multi_link, fp);
> kprobe_multi_link_prog_run(link, entry_ip, regs);
> }
Strictly speaking this can explode if this function is one without ENDBR
and it's on a page-edge and -1 is a guard page or something silly like
that (could conceivably happen for a module or so).
I'm also thinking this function might be a bit clearer if the argument
were called fentry_ip -- that way it would be clearer this is an ftrace
__fentry__ ip.
The canonical way to get at +0 would be something like:
kallsyms_lookup_size_offset(fentry_ip, &size, &offset);
entry_ip = fentry_ip - offset;
But I appreciate that might be too expensive here; is this a hot path?
Could you store this information in struct bpf_kprobe_multi_link?
next prev parent reply other threads:[~2022-09-09 11:49 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-09 10:12 [PATCHv3 bpf-next 0/6] bpf: Fixes for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-09-09 10:12 ` [PATCHv3 bpf-next 1/6] kprobes: Add new KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag Jiri Olsa
2022-09-09 10:12 ` [PATCHv3 bpf-next 2/6] ftrace: Keep the resolved addr in kallsyms_callback Jiri Olsa
2022-09-09 10:12 ` [PATCHv3 bpf-next 3/6] bpf: Use given function address for trampoline ip arg Jiri Olsa
2022-09-09 11:30 ` Peter Zijlstra
2022-09-09 11:40 ` Jiri Olsa
2022-09-09 10:12 ` [PATCHv3 bpf-next 4/6] bpf: Adjust kprobe_multi entry_ip for CONFIG_X86_KERNEL_IBT Jiri Olsa
2022-09-09 11:49 ` Peter Zijlstra [this message]
2022-09-09 12:25 ` Jiri Olsa
2022-09-09 10:12 ` [PATCHv3 bpf-next 5/6] bpf: Return value in kprobe get_func_ip only for entry address Jiri Olsa
2022-09-09 11:57 ` Peter Zijlstra
2022-09-09 10:12 ` [PATCHv3 bpf-next 6/6] selftests/bpf: Fix get_func_ip offset test for CONFIG_X86_KERNEL_IBT Jiri Olsa
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