Date: Thu, 3 Aug 2017 17:15:50 +0200 From: Michal Hocko <mhocko@...nel.org> To: Igor Stoppa <igor.stoppa@...wei.com> Cc: Jerome Glisse <jglisse@...hat.com>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, linux-security-module@...r.kernel.org, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Kees Cook <keescook@...gle.com> Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator On Thu 03-08-17 18:06:11, Igor Stoppa wrote: > > > On 03/08/17 17:47, Jerome Glisse wrote: > > On Thu, Aug 03, 2017 at 03:55:50PM +0200, Michal Hocko wrote: > >> On Thu 03-08-17 15:20:31, Igor Stoppa wrote: > > [...] > > >>> I am confused about this: if "private2" is a pointer, but when I get an > >>> address, I do not even know if the address represents a valid pmalloc > >>> page, how can i know when it's ok to dereference "private2"? > >> > >> because you can make all pages which back vmalloc mappings have vm_area > >> pointer set. > > > > Note that i think this might break some device driver that use vmap() > > i think some of them use private field to store device driver specific > > informations. But there likely is an unuse field in struct page that > > can be use for that. > > This increases the unease from my side ... it looks like there is no way > to fully understand if a field is really used or not, without having > deep intimate knowledge of lots of code that is only marginally involved :-/ welcome to the struct page heaven... > Similarly, how would I be able to specify what would be the correct way > to decide the member of the union to use for handling the field? I would check the one where we have mapping. It is rather unlikely vmalloc users would touch this one. -- Michal Hocko SUSE Labs
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