linux-kernel - Re: [uaccess] 780464aed0: WARNING:at_arch/x86/include/asm/uaccess.h:#strnlen

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Message-Id: <20190305172241.2eef39c6ca74d09120bbbcad@kernel.org>
Date:   Tue, 5 Mar 2019 17:22:41 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        kernel test robot <lkp@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Shuah Khan <shuah@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Changbin Du <changbin.du@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Nadav Amit <namit@...are.com>,
        Joel Fernandes <joel@...lfernandes.org>, yhs@...com, lkp@...org
Subject: Re: [uaccess] 780464aed0:
 WARNING:at_arch/x86/include/asm/uaccess.h:#strnlen_user/0x

On Tue, 5 Mar 2019 11:36:35 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Mon, 4 Mar 2019 10:59:22 -0800
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> I think the better way to do this is allowing strncpy_from_user()
> if some conditions are match, like
> 
>  - strncpy_from_user() will be able to copy user memory with set_fs(USER_DS)
>  - strncpy_from_user() can copy kernel memory with set_fs(KERNEL_DS)
>  - strncpy_from_user() can access unsafe memory in IRQ context if
>    pagefault is disabled.
> 
> This is almost done, except for CONFIG_DEBUG_ATOMIC_SLEEP=y on x86.
> 
> So, what about adding a condition to WARN_ON_IN_IRQ() like below
> instead of introducing user_access_ok() ?
> 
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 780f2b42c8ef..ec0f0b74c9ab 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -70,7 +70,7 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
>  })
>  
>  #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> -# define WARN_ON_IN_IRQ()      WARN_ON_ONCE(!in_task())
> +# define WARN_ON_IN_IRQ()      WARN_ON_ONCE(pagefault_disabled() && !in_task())

Oops, I meant !pagefault_disabled() && !in_task().

>  #else
>  # define WARN_ON_IN_IRQ()
>  #endif
> 
> Of course we have to move pagefault_disabled() macro in somewhere better place.

And I think we don't need it. anyway the macro is referenced via linux/uaccess.h.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>