Date: Fri, 26 Jan 2018 11:36:30 -0500 From: Boris Lukashev <blukashev@...pervictus.com> To: Igor Stoppa <igor.stoppa@...wei.com> Cc: Jerome Glisse <jglisse@...hat.com>, Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>, Michal Hocko <mhocko@...nel.org>, Laura Abbott <labbott@...hat.com>, Christoph Hellwig <hch@...radead.org>, Matthew Wilcox <willy@...radead.org>, Christoph Lameter <cl@...ux.com>, linux-security-module <linux-security-module@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, kernel list <linux-kernel@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH 4/6] Protectable Memory On Fri, Jan 26, 2018 at 7:28 AM, Igor Stoppa <igor.stoppa@...wei.com> wrote: > On 25/01/18 17:38, Jerome Glisse wrote: >> On Thu, Jan 25, 2018 at 10:14:28AM -0500, Boris Lukashev wrote: >>> On Thu, Jan 25, 2018 at 6:59 AM, Igor Stoppa <igor.stoppa@...wei.com> wrote: >> >> [...] >> >>> DMA/physmap access coupled with a knowledge of which virtual mappings >>> are in the physical space should be enough for an attacker to bypass >>> the gating mechanism this work imposes. Not trivial, but not >>> impossible. Since there's no way to prevent that sort of access in >>> current hardware (especially something like a NIC or GPU working >>> independently of the CPU altogether) > > [...] > >> I am not saying that this can not happen but that we are trying our best >> to avoid it. > > How about an opt-in verification, similar to what proposed by Boris > Lukashev? > > When reading back the data, one could access the pointer directly and > bypass the verification, or could use a function that explicitly checks > the integrity of the data. > > Starting from an unprotected kmalloc allocation, even just turning the > data into R/O is an improvement, but if one can afford the overhead of > performing the verification, why not? > I like the idea of making the verification call optional for consumers allowing for fast/slow+hard paths depending on their needs. Cant see any additional vectors for abuse (other than the original ones effecting out-of-band modification) introduced by having verify/normal callers, but i've not had enough coffee yet. Any access races or things like that come to mind for anyone? Shouldn't happen with a write-once allocation, but again, lacking coffee. > It would still be better if the service was provided by the library, > instead than implemented by individual users, I think. > > -- > igor -Boris
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