From: Luiz Capitulino <lcapitul...@redhat.com> Subject: Re: [Qemu-devel] qmp: dump-guest-memory: -p option has issues, fix it or drop it? Date: Wed, 19 Sep 2012 10:23:26 -0300
> On Wed, 19 Sep 2012 11:26:51 +0900 (JST) > HATAYAMA Daisuke <d.hatay...@jp.fujitsu.com> wrote: > >> From: Wen Congyang <we...@cn.fujitsu.com> >> Subject: Re: [Qemu-devel] qmp: dump-guest-memory: -p option has issues, fix >> it or drop it? >> Date: Wed, 19 Sep 2012 10:07:04 +0800 >> >> > At 09/19/2012 08:18 AM, Luiz Capitulino Wrote: >> >> On Tue, 18 Sep 2012 16:13:30 -0500 >> >> Anthony Liguori <anth...@codemonkey.ws> wrote: >> >> >> >>> Markus Armbruster <arm...@redhat.com> writes: >> >>> >> >>>> Jan Kiszka <jan.kis...@siemens.com> writes: >> >>>> >> How about dropping making a whole list of memory maps at the same >> time, and how about rewriting the code so that it always has at most >> one memory mapping by merging virtually consequtive chunks? If >> possible, only 40 bytes is needed. > > It already merges contiguous addresses and addresses that fall in > the same range. It can also skip addresses due to a few reasons (I/O > page, not present page, etc), which makes the problem very unlikely > in practice. > I've noticed this locally, thanks. > Our concern is with guests intentionally trying to make qemu allocate > more memory. My idea is not to create a list of a whole memory mapping. This needs O(n), which can be a target of attackers. If possible to drop this list, memory consumption is O(1), and there's no room for any guest to attack. Concretely, the processing becomes: first walking page tables to identify a memory mapping corresponding to a PT_LOAD entry, then write it when reaching the part belonging to a next PT_LOAD entry. But the problem I've noticed just now..., is that then we need to walk page tables twice: first for writing program header tables and second for writing memory part. Code becomes not clean. Thanks. HATAYAMA, Daisuke
