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;
Subject: Re: linux-next: Tree for Nov 7
To:     Michal Hocko <mhocko@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     Joel Stanley <joel@jms.id.au>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        "James E.J. Bottomley" <jejb@parisc-linux.org>,
        Helge Deller <deller@gmx.de>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        "David S. Miller" <davem@davemloft.net>,
        Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, linux-mips@linux-mips.org,
        linux-parisc@vger.kernel.org, linux-sh@vger.kernel.org,
        sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org
References: <CACPK8Xfd4nqkf=Lk3n6+TNHAAi327r0dkUfGypZ3TpR0LqfS4Q@mail.gmail.com>
 <20171108142050.7w3yliulxjeco3b7@dhcp22.suse.cz>
 <20171110123054.5pnefm3mczsfv7bz@dhcp22.suse.cz>
 <CACPK8Xe5uUKEytkRiszdX511b_cYTD-z3X=ZsMcNJ-NOYnXfuQ@mail.gmail.com>
 <20171113092006.cjw2njjukt6limvb@dhcp22.suse.cz>
 <20171113094203.aofz2e7kueitk55y@dhcp22.suse.cz>
 <87lgjawgx1.fsf@concordia.ellerman.id.au>
 <20171113120057.555mvrs4fjq5tyng@dhcp22.suse.cz>
 <20171113151641.yfqrecpcxllpn5mq@dhcp22.suse.cz>
 <20171113154939.6ui2fmpokpm7g4oj@dhcp22.suse.cz>
 <20171113160637.jhekbdyfpccme3be@dhcp22.suse.cz>
From:   Khalid Aziz <khalid.aziz@oracle.com>
Organization: Oracle Corp
Message-ID: <c52fa249-9583-18a2-cbac-28abfb23d5a5@oracle.com>
Date:   Mon, 13 Nov 2017 09:35:22 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.4.0
MIME-Version: 1.0
In-Reply-To: <20171113160637.jhekbdyfpccme3be@dhcp22.suse.cz>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 11/13/2017 09:06 AM, Michal Hocko wrote:
> OK, so this one should take care of the backward compatibility while
> still not touching the arch code
> ---
> commit 39ff9bf8597e79a032da0954aea1f0d77d137765
> Author: Michal Hocko <mhocko@suse.com>
> Date:   Mon Nov 13 17:06:24 2017 +0100
> 
>      mm: introduce MAP_FIXED_SAFE
>      
>      MAP_FIXED is used quite often but it is inherently dangerous because it
>      unmaps an existing mapping covered by the requested range. While this
>      might be might be really desidered behavior in many cases there are
>      others which would rather see a failure than a silent memory corruption.
>      Introduce a new MAP_FIXED_SAFE flag for mmap to achive this behavior.
>      It is a MAP_FIXED extension with a single exception that it fails with
>      ENOMEM if the requested address is already covered by an existing
>      mapping. We still do rely on get_unmaped_area to handle all the arch
>      specific MAP_FIXED treatment and check for a conflicting vma after it
>      returns.
>      
>      Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> ...... deleted .......
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 680506faceae..aad8d37f0205 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1358,6 +1358,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>   	if (mm->map_count > sysctl_max_map_count)
>   		return -ENOMEM;
>   
> +	/* force arch specific MAP_FIXED handling in get_unmapped_area */
> +	if (flags & MAP_FIXED_SAFE)
> +		flags |= MAP_FIXED;
> +
>   	/* Obtain the address to map to. we verify (or select) it and ensure
>   	 * that it represents a valid section of the address space.
>   	 */

Do you need to move this code above:

         if (!(flags & MAP_FIXED))
                 addr = round_hint_to_min(addr);

         /* Careful about overflows.. */
         len = PAGE_ALIGN(len);
         if (!len)
                 return -ENOMEM;

Not doing that might mean the hint address will end up being rounded for 
MAP_FIXED_SAFE which would change the behavior from MAP_FIXED.

--
Khalid

From 1583967638937488736@xxx Mon Nov 13 16:07:35 +0000 2017
X-GM-THRID: 1583423641769727671
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread