Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 5 Mar 2019 10:07:29 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        kernel test robot <lkp@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Shuah Khan <shuah@kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Changbin Du <changbin.du@gmail.com>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Nadav Amit <namit@vmware.com>,
        Joel Fernandes <joel@joelfernandes.org>, yhs@fb.com, lkp@01.org
Subject: Re: [uaccess] 780464aed0:
 WARNING:at_arch/x86/include/asm/uaccess.h:#strnlen_user/0x
Message-ID: <20190305090729.GF32477@hirez.programming.kicks-ass.net>
References: <155136980507.2968.15165201054223875356.stgit@devbox>
 <20190303173954.kliegojbuigqi5tn@inn2.lkp.intel.com>
 <CAHk-=wij8VLupHh1U-fFhFBjin9Fch3mG2_2=aL9h1L+WBvm2g@mail.gmail.com>
 <20190304101434.8429ffffb17813c0e7930130@kernel.org>
 <CAHk-=whYMvevgF4yh7uhQug=Wt1A1Eg7abyM=RCi=bQiqiMBvQ@mail.gmail.com>
 <20190304180610.2d4f6f08d9ad89d6abae3597@kernel.org>
 <CAHk-=wiQM84VsAiw92UWyQZTQxr+F032Gm5BiFBXk7tC+LQohQ@mail.gmail.com>
 <20190305113635.18f80ea3b1f4fca54b9d21e4@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190305113635.18f80ea3b1f4fca54b9d21e4@kernel.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Mar 05, 2019 at 11:36:35AM +0900, Masami Hiramatsu wrote:
> I think the better way to do this is allowing strncpy_from_user()
O
> 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())

That doesn't make any kind of sense to me; see faulthandler_disabled().
IOW. interrupt (and any atomic context really) won't take faults anyway.

I dislike that whole KERNEL_DS thing, but obviously that's not something
that's going away.

Would something like:

	WARN_ON_ONCE(!(in_task || segment_eq(get_fs(), USER_DS)))

Work? Then we allow KERNEL_DS in task context, but for interrupt and
others require USER_DS.