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Subject: Re: [PATCH] riscv: keep interrupts disabled for BREAKPOINT exception
To:     Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
References: <20210330021624.2b776386@xhacker>
 <20210330183316.942215efe8e6e8455ad14113@kernel.org>
 <20210331222244.45a5807c@xhacker>
From:   "liaochang (A)" <liaochang1@huawei.com>
CC:     Masami Hiramatsu <mhiramat@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Guo Ren <guoren@linux.alibaba.com>,
        <linux-riscv@lists.infradead.org>, <linux-kernel@vger.kernel.org>
Message-ID: <096752a7-21f9-8339-2e76-8c65859fa1d7@huawei.com>
Date:   Thu, 1 Apr 2021 16:49:47 +0800
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Hi Jisheng,

?? 2021/3/31 22:22, Jisheng Zhang д??:
> On Tue, 30 Mar 2021 18:33:16 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
>> Hi Jisheng,
> 
> Hi Masami,
> 
>>
>> On Tue, 30 Mar 2021 02:16:24 +0800
>> Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:
>>
>>> From: Jisheng Zhang <jszhang@kernel.org>
>>>
>>> Current riscv's kprobe handlers are run with both preemption and
>>> interrupt enabled, this violates kprobe requirements. Fix this issue
>>> by keeping interrupts disabled for BREAKPOINT exception.  
>>
>> Not only while the breakpoint exception but also until the end of
>> the single step (maybe you are using __BUG_INSN_32 ??) need to be
>> disable interrupts. Can this do that?
>>
> 
> interrupt is disabled during "single step" by kprobes_save_local_irqflag()
> and kprobes_restore_local_irqflag(). The code flow looks like: 
> 
> do_trap_break()   // for bp
>   kprobe_breakpoint_handler()
>     setup_singlestep()
>       kprobes_restore_local_irqflag()
> 
> do_trap_break()  // for ss
>   kprobe_single_step_handler()
>     kprobes_restore_local_irqflag()

Recently, kernel hit BUG_ON() on QEMU after I install a probe at "sys_read" via kprobe,
accoriding to my debugging and analysis it looks like caused by the "irq disable" operation for single-stepping.

I present a detailed description about this problem in the mail with title "[PATCH] riscv/kprobe: fix kernel panic when invoking sys_read traced by kprobe".
Looking forward to some feedback,Thanks.

BR,
Liao Chang
> 
> Thanks
> 
> 
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