Date: Thu, 3 Aug 2017 17:41:24 +0300 From: Igor Stoppa <igor.stoppa@...wei.com> To: Michal Hocko <mhocko@...nel.org> 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 03/08/17 16:55, Michal Hocko wrote: > On Thu 03-08-17 15:20:31, Igor Stoppa wrote: >> On 03/08/17 14:48, Michal Hocko wrote: >>> On Thu 03-08-17 13:11:45, Igor Stoppa wrote: [...] >>>> But, to reply more specifically to your advice, yes, I think I could add >>>> a flag to vm_struct and then retrieve its value, for the address being >>>> processed, by passing through find_vm_area(). >>> >>> ... and you can store vm_struct pointer to the struct page there >> >> "there" as in the new field of the union? >> btw, what would be a meaningful name, since "private" is already taken? >> >> For simplicity, I'll use, for now, "private2" > > why not explicit vm_area? ok :-) >>> and you won't need to do the slow find_vm_area. I haven't checked >> very closely >>> but this should be possible in principle. I guess other callers might >>> benefit from this as well. >> >> 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. Ah, now I see, I had missed that the field would be set for *all* pages backed by vmalloc. So, given a pointer, I still have to figure out if it refers to a vmalloc area or not. However, that is something I need to do anyway, to get the reference to the corresponding page struct, in case it is indeed a vmalloc address. -- thanks, igor
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