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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Fri, 13 Dec 2019 10:12:29 +0100
Message-ID: <CAK8P3a1nLz2FDxw28DBXVma9E2saWpGtt+y6tYm4jros6TUF6w@mail.gmail.com>
Subject: Re: [PATCH V2] MIPS: Add get_thread_area syscall
To:     Guoyun Sun <sunguoyun@loongson.cn>
Cc:     Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paulburton@kernel.org>,
        James Hogan <jhogan@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Xuefeng Li <lixuefeng@loongson.cn>
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On Fri, Dec 13, 2019 at 9:30 AM Guoyun Sun <sunguoyun@loongson.cn> wrote:

Thanks for fixing the numbers. On second look, I saw another problem:

> diff --git a/arch/mips/kernel/syscall.c b/arch/mips/kernel/syscall.c
> index c333e57..20bf4c5 100644
> --- a/arch/mips/kernel/syscall.c
> +++ b/arch/mips/kernel/syscall.c
> @@ -94,6 +94,16 @@ SYSCALL_DEFINE1(set_thread_area, unsigned long, addr)
>         return 0;
>  }
>
> +SYSCALL_DEFINE1(get_thread_area, unsigned long __user *, u_info)
> +{
> +       struct thread_info *ti = task_thread_info(current);
> +
> +       if (copy_to_user(u_info, &(ti->tp_value), sizeof(ti->tp_value)))
> +               return -EFAULT;
> +
> +       return 0;
> +}
> +

This won't work for compat mode, when tp_value is a different size
in kernel and user space. You could either add a COMPAT_SYSCALL_DEFINE1()
variant, or handle it like

        if (in_compat_syscall())
                   return put_user(ti->tp_value, (__u32 *)u_info);
        return put_user(ti->tp_value, u_info);


      Arnd