netdev - Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW

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Date:   Tue, 27 Mar 2018 15:48:35 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     <davem@...emloft.net>, <daniel@...earbox.net>,
        <torvalds@...ux-foundation.org>, <peterz@...radead.org>,
        <netdev@...r.kernel.org>, <kernel-team@...com>,
        <linux-api@...r.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT

On 3/27/18 2:04 PM, Steven Rostedt wrote:
>
> +#ifdef CONFIG_BPF_EVENTS
> +#define BPF_RAW_TP() . = ALIGN(8);		\
> +			 VMLINUX_SYMBOL(__start__bpf_raw_tp) = .;	\
> +			 KEEP(*(__bpf_raw_tp_map))			\
> +			 VMLINUX_SYMBOL(__stop__bpf_raw_tp) = .;

that looks to be correct, but something wrong with it.

Can you try your mini test with kasan on ?

I'm seeing this crash:
test_stacktrace_[   18.760662] start ffffffff84642438 stop ffffffff84644f60
map_raw_tp:PASS:[   18.761467] i 1 btp->tp cccccccccccccccc
prog_load raw tp[   18.762064] kasan: CONFIG_KASAN_INLINE enabled
  0 nsec
[   18.762704] kasan: GPF could be caused by NULL-ptr deref or user 
memory access
[   18.765125] general protection fault: 0000 [#1] SMP KASAN PTI
[   18.765830] Modules linked in:
[   18.778358] Call Trace:
[   18.778674]  bpf_raw_tracepoint_open.isra.27+0x92/0x380

for some reason the start_bpf_raw_tp is off by 8.
Not sure how it works for you.

(gdb) p &__bpf_trace_tp_map_sys_exit
$10 = (struct bpf_raw_event_map *) 0xffffffff84642440 
<__bpf_trace_tp_map_sys_exit>

(gdb)  p &__start__bpf_raw_tp
$7 = (<data variable, no debug info> *) 0xffffffff84642438

(gdb)  p (void*)(&__start__bpf_raw_tp)+8
$11 = (void *) 0xffffffff84642440 <__bpf_trace_tp_map_sys_exit>