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From:   Vincent Chen <deanbo422@gmail.com>
Date:   Thu, 26 Apr 2018 11:02:54 +0800
Message-ID: <CAJsyPhzSgPebAtP7m8Dsidy+2Lj6mKb7J-dPqHmFVzWv6Q55YQ@mail.gmail.com>
Subject: Re: [PATCH] signal/nds32: More information in do_revinsn
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-api@vger.kernel.org, Vincent Chen <vincentc@andestech.com>,
        Greentime Hu <greentime@andestech.com>,
        Arnd Bergmann <arnd@arndb.de>
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2018-04-26 0:13 GMT+08:00 Eric W. Biederman <ebiederm@xmission.com>:
>
> While reviewing f6ed1ecad56f ("signal/nds32: Use force_sig(SIGILL) in do_revisn")
> Vincent Chen asked if it was possible to provide more information in do_revinsn
> with force_sig_fault.
>
> That seems reasonable and the appropirate si_code appears to be
> ILL_ILLOPC (illegal opcode) as the printk indicates this code path
> is triggered when a reserved instruction is exectured.
>

I think error code is set as ILL_ILLOPC is a good choice for normal
reserved instruction
but it seems a little bit inappropriate for nds32. For nds32 reserved
exception, It is possibly
triggered by illegal opcode, operand and immediate. Unfortunately,
do_revisn() can not
identify the actual reason now. Therefore, I chose ILLTRAP to avoid
confusing user when
the reserved exception is cauesd by wrong immediate or operand.


> So update do_revinsn to use force_sig_fault(SIGILL, ILL_ILLOPC, ...).
> Giving userspace a much better experience when soemone attempts
> to execute a reserved instruction.
>
> Cc: Greentime Hu <green.hu@gmail.com>
> Cc: Vincent Chen <deanbo422@gmail.com>
> Suggested-by: Vincent Chen <deanbo422@gmail.com>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>
> Vincent I have updated this from your suggestion to use
> ILL_ILLOPC as that appears the more appropriate si_code.
> Normally I expect you could just update your nds32 tree and
> make this kind of change but since I am touching this code anyway I will
> be happy to take this change along with the others.
>
> Does this look good to you?
>

It is fine to commit this change along with the others.

Vincent Chen


>  arch/nds32/kernel/traps.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/nds32/kernel/traps.c b/arch/nds32/kernel/traps.c
> index a6205fd4db52..5c2f61835ab9 100644
> --- a/arch/nds32/kernel/traps.c
> +++ b/arch/nds32/kernel/traps.c
> @@ -349,7 +349,8 @@ void do_revinsn(struct pt_regs *regs)
>         show_regs(regs);
>         if (!user_mode(regs))
>                 do_exit(SIGILL);
> -       force_sig(SIGILL, current);
> +       force_sig_fault(SIGILL, ILL_ILLOPC,
> +                       (void __user *)instruction_pointer(regs), current);
>  }
>
>  #ifdef CONFIG_ALIGNMENT_TRAP
> --
> 2.14.1
>