Date: Tue, 12 Sep 2017 15:07:29 +0800 From: Yisheng Xie <xieyisheng1@...wei.com> To: Tycho Andersen <tycho@...ker.com> CC: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <kernel-hardening@...ts.openwall.com>, Marco Benatto <marco.antonio.780@...il.com>, Juerg Haefliger <juerg.haefliger@...onical.com> Subject: Re: [PATCH v6 00/11] Add support for eXclusive Page Frame Ownership Hi Tycho, On 2017/9/11 23:02, Tycho Andersen wrote: > Hi Yisheng, > > On Mon, Sep 11, 2017 at 06:34:45PM +0800, Yisheng Xie wrote: >> Hi Tycho , >> >> On 2017/9/8 1:35, Tycho Andersen wrote: >>> Hi all, >>> >>> Here is v6 of the XPFO set; see v5 discussion here: >>> https://lkml.org/lkml/2017/8/9/803 >>> >>> Changelogs are in the individual patch notes, but the highlights are: >>> * add primitives for ensuring memory areas are mapped (although these are quite >>> ugly, using stack allocation; I'm open to better suggestions) >>> * instead of not flushing caches, re-map pages using the above >>> * TLB flushing is much more correct (i.e. we're always flushing everything >>> everywhere). I suspect we may be able to back this off in some cases, but I'm >>> still trying to collect performance numbers to prove this is worth doing. >>> >>> I have no TODOs left for this set myself, other than fixing whatever review >>> feedback people have. Thoughts and testing welcome! >> >> According to the paper of Vasileios P. Kemerlis et al, the mainline kernel >> will not set the Pro. of physmap(direct map area) to RW(X), so do we really >> need XPFO to protect from ret2dir attack? > > I guess you're talking about section 4.3? Yes > They mention that that x86 > only gets rw, but that aarch64 is rwx still. IIRC, the in kernel of v4.13 the aarch64 is not rwx, I will check it. > > But in either case this still provides access protection, similar to > SMAP. Also, if I understand things correctly the protections are > unmanaged, so a page that had the +x bit set at some point, it could > be used for ret2dir. So you means that the Pro. of direct map area maybe changed to +x, then ret2dir attack can use it? Thanks Yisheng Xie
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