linux-kernel - Re: Checkpoint/restart (was Re: [PATCH 0/4] - v2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 10 Jul 2008 12:47:32 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	Oren Laadan <orenl@...columbia.edu>,
	Kirill Korotaev <dev@...allels.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Nadia.Derbey@...l.net,
	Andrew Morton <akpm@...ux-foundation.org>,
	nick@...k-andrew.net, Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: Checkpoint/restart (was Re: [PATCH 0/4] - v2 - Object creation
	with a specified id)

On Thu, 2008-07-10 at 12:21 -0700, Eric W. Biederman wrote:
> > Are we talking about the VMA itself, or the memory backing the VMA?
> 
> The memory backing the VMA.  We need to store the page protections
> that the memory was mapped with as well now that you point it out.  A
> VMA is not user space visible, which is why we can arbitrarily split
> and merge VMAs.

It is visible with /proc/$pid/{maps,smaps,numamaps?}.  That's the only
efficient way I know of from userspace to figure out where userspace's
memory is and if it *is* file backed, and what the permissions are.

We also can't truly split them arbitrarily because the memory cost of
the VMAs themselves might become too heavy (the remap_file_pages()
problem).

It gets trickier when things are also private mappings in addition to
being in a file-backed VMA.  We *do* need to checkpoint those, but only
the pages to which there was a write.

There's also the problem of restoring things read-only, but VM_MAYWRITE.
If there's a high level of (non-COW'd) sharing of these anonymous areas,
we may not be able to even restore the set of processes unless we can
replicate the sharing.  We might run out of memory if the sharing isn't
replicated.

Memory is fun! :)

-- Dave

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/