From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] xen/x86: Remap text/data/bss with appropriate permissions
Date: Thu, 17 Mar 2016 16:15:44 +0000 [thread overview]
Message-ID: <56EAD830.8090003@citrix.com> (raw)
In-Reply-To: <56EADC3A02000078000DDF75@prv-mh.provo.novell.com>
On 17/03/16 15:32, Jan Beulich wrote:
>>>> On 17.03.16 at 15:44, <andrew.cooper3@citrix.com> wrote:
>> On 17/03/16 14:31, Jan Beulich wrote:
>>> Also - do we really want to make this code dependent on
>>> map_pages_to_xen() not intermediately zapping the mappings
>>> being changed?
>> Do you mean "immediately"?
> No.
>
>> As far as I can tell, it is guaranteed to be safe, even when remapping
>> the code section. Updates to the live pagetables are using atomic
>> writes, and I didn't spot a point which would end up with a transient
>> non-present mapping.
> But we may, at some point and for whatever reason, come to make
> the function zap the mapping (i.e. clear the present bit), flush, and
> only the re-establish the new mapping.
This change is temporary until I can fix the legacy boot issue and
reintroduce the proper 2M functionality.
If someone in the future wants to change the behaviour of
map_pages_to_xen() then we can reconsider. However, I think it is
unlikely that this will actually happen at all, and if it ever does, I
hope to have already fixed the 2M alignment and deleted this change.
This change is a big security improvement, and absolutely should be
taken, especially as the current implementation of map_pages_to_xen() is
safe.
~Andrew
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-03-17 16:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-17 12:43 [PATCH] xen/x86: Remap text/data/bss with appropriate permissions Andrew Cooper
2016-03-17 12:43 ` [PATCH] DO NOT APPLY - debug keys for inspecting Xen mappings Andrew Cooper
2016-03-17 14:31 ` [PATCH] xen/x86: Remap text/data/bss with appropriate permissions Jan Beulich
2016-03-17 14:44 ` Andrew Cooper
2016-03-17 15:32 ` Jan Beulich
2016-03-17 16:15 ` Andrew Cooper [this message]
2016-03-18 7:25 ` Jan Beulich
2016-03-18 19:49 ` [PATCH v2] " Andrew Cooper
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=56EAD830.8090003@citrix.com \
--to=andrew.cooper3@citrix.com \
--cc=JBeulich@suse.com \
--cc=xen-devel@lists.xen.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).