From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Jann Horn <jannh@google.com>,
linux-man@vger.kernel.org, mhocko@kernel.org,
jhubbard@nvidia.com, akpm@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org
Cc: mtk.manpages@gmail.com
Subject: Re: [PATCH] mmap.2: MAP_FIXED is okay if the address range has been reserved
Date: Thu, 12 Apr 2018 20:32:40 +0200 [thread overview]
Message-ID: <3ff7472c-23c8-402b-ddfb-871a749c5016@gmail.com> (raw)
In-Reply-To: <20180412153941.170849-1-jannh@google.com>
Hello Jann,
On 04/12/2018 05:39 PM, Jann Horn wrote:
> Clarify that MAP_FIXED is appropriate if the specified address range has
> been reserved using an existing mapping, but shouldn't be used otherwise.
>
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
> man2/mmap.2 | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/man2/mmap.2 b/man2/mmap.2
> index bef8b4432..80c9ec285 100644
> --- a/man2/mmap.2
> +++ b/man2/mmap.2
> @@ -253,8 +253,9 @@ Software that aspires to be portable should use this option with care,
> keeping in mind that the exact layout of a process's memory mappings
> is allowed to change significantly between kernel versions,
> C library versions, and operating system releases.
> -Furthermore, this option is extremely hazardous (when used on its own),
> -because it forcibly removes preexisting mappings,
> +This option should only be used when the specified memory region has
> +already been reserved using another mapping; otherwise, it is extremely
> +hazardous because it forcibly removes preexisting mappings,
> making it easy for a multithreaded process to corrupt its own address space.
> .IP
> For example, suppose that thread A looks through
> @@ -284,13 +285,15 @@ and the PAM libraries
> .UR http://www.linux-pam.org
> .UE .
> .IP
> -Newer kernels
> -(Linux 4.17 and later) have a
> +For cases in which the specified memory region has not been reserved using an
> +existing mapping, newer kernels (Linux 4.17 and later) provide an option
> .B MAP_FIXED_NOREPLACE
> -option that avoids the corruption problem; if available,
> -.B MAP_FIXED_NOREPLACE
> -should be preferred over
> -.BR MAP_FIXED .
> +that should be used instead; older kernels require the caller to use
> +.I addr
> +as a hint (without
> +.BR MAP_FIXED )
> +and take appropriate action if the kernel places the new mapping at a
> +different address.
> .TP
> .BR MAP_FIXED_NOREPLACE " (since Linux 4.17)"
> .\" commit a4ff8e8620d3f4f50ac4b41e8067b7d395056843
Thanks! Nice patch! Applied.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2018-04-12 18:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 15:39 [PATCH] mmap.2: MAP_FIXED is okay if the address range has been reserved Jann Horn
2018-04-12 18:32 ` Michael Kerrisk (man-pages) [this message]
2018-04-12 18:33 ` John Hubbard
2018-04-12 18:37 ` Michael Kerrisk (man-pages)
2018-04-12 18:49 ` Jann Horn
2018-04-12 18:59 ` John Hubbard
2018-04-12 19:18 ` Jann Horn
2018-04-12 19:24 ` John Hubbard
2018-04-13 6:43 ` Michael Kerrisk (man-pages)
2018-04-13 6:49 ` Michal Hocko
2018-04-13 15:04 ` Jann Horn
2018-04-13 16:04 ` Michal Hocko
2018-04-13 16:05 ` Jann Horn
2018-04-13 16:17 ` Jann Horn
2018-04-16 10:07 ` Michal Hocko
2018-04-16 13:55 ` Jann Horn
2018-04-16 19:18 ` Michal Hocko
2018-04-16 19:30 ` Jann Horn
2018-04-16 19:57 ` Michal Hocko
2018-04-16 20:17 ` Jann Horn
2018-04-16 21:11 ` Michal Hocko
2018-04-16 21:12 ` Jann Horn
2018-04-17 6:23 ` Michal Hocko
2018-05-02 13:06 ` Michael Kerrisk (man-pages)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3ff7472c-23c8-402b-ddfb-871a749c5016@gmail.com \
--to=mtk.manpages@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=jannh@google.com \
--cc=jhubbard@nvidia.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-man@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).