Messages in this thread | | | From | Dmitry Vyukov <> | Date | Thu, 13 Feb 2020 09:44:37 +0100 | Subject | Re: [RFC PATCH v2] UML: add support for KASAN under x86_64 |
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On Thu, Feb 13, 2020 at 9:19 AM Johannes Berg <johannes@sipsolutions.net> wrote: > > On Wed, 2020-02-12 at 16:37 -0800, Patricia Alfonso wrote: > > > > > That also means if I have say 512MB memory allocated for UML, KASAN will > > > use an *additional* 64, unlike on a "real" system, where KASAN will take > > > about 1/8th of the available physical memory, right? > > > > > Currently, the amount of shadow memory allocated is a constant based > > on the amount of user space address space in x86_64 since this is the > > host architecture I have focused on. > > Right, but again like below - that's just mapped, not actually used. But > as far as I can tell, once you actually start running and potentially > use all of your mem=1024 (MB), you'll actually also use another 128MB on > the KASAN shadow, right? > > Unlike, say, a real x86_64 machine where if you just have 1024 MB > physical memory, the KASAN shadow will have to fit into that as well.
Depends on what you mean by "real" :) Real user-space ASAN will also reserve 1/8th of 47-bit VA on start (16TB). This implementation seems to be much closer to user-space ASAN rather than to x86_64 KASAN (in particular it seems to be mostly portable across archs and is not really x86-specific, which is good). I think it's reasonable and good, but the implementation difference with other kernel arches may be worth noting somewhere in comments.
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