Date: Tue, 17 Jan 2017 17:44:07 +0000 From: "Reshetova, Elena" <elena.reshetova@...el.com> To: Kees Cook <keescook@...omium.org> CC: Peter Zijlstra <peterz@...radead.org>, AKASHI Takahiro <takahiro.akashi@...aro.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "arnd@...db.de" <arnd@...db.de>, "tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com" <mingo@...hat.com>, "Anvin, H Peter" <h.peter.anvin@...el.com>, "will.deacon@....com" <will.deacon@....com>, "dwindsor@...il.com" <dwindsor@...il.com>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, "ishkamiel@...il.com" <ishkamiel@...il.com> Subject: RE: [RFC PATCH 08/19] kernel, mm: convert from atomic_t to refcount_t > On Mon, Jan 16, 2017 at 8:16 AM, Reshetova, Elena > <elena.reshetova@...el.com> wrote: > >> On Thu, Jan 12, 2017 at 02:11:15PM +0900, AKASHI Takahiro wrote: > >> > On Wed, Jan 11, 2017 at 02:55:21PM -0800, Kees Cook wrote: > >> > > On Wed, Jan 11, 2017 at 1:42 PM, Kees Cook <keescook@...omium.org> > >> wrote: > >> > > > I can see if it'll cherry-pick cleanly, I assume it will. :) > >> > > > >> > > It cherry-picked cleanly. However, I made several changes: > >> > > > >> > > - I adjusted Peter's author email (it had extra s around). > >> > > - I fixed all of the commit subjects (Peter's were missing). > >> > > - I added back "kref: Add KREF_INIT()" since it seems to have been > >> > > lost and mixed into other patches that would break bisection > >> > > > >> > > It's here now, please work from this version: > >> > > > >> > > > >> > http://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=kspp/hardened- > >> atomic > >> > > >> > I gave it a spin on arm64. > >> > It can compile with a change to smp.c that I mentioned before, > >> > but the boot failed. I've not dug into it. > >> > > >> > ===8<=== > >> > [ 3.578618] refcount_t: increment on 0; use-after-free. > >> > [ 3.579165] ------------[ cut here ]------------ > >> > [ 3.579254] WARNING: CPU: 0 PID: 1 at > /home/akashi/arm/armv8/linaro/linux- > >> aarch64/include/linux/refcount.h:109 unx_create+0x8c/0xc0 > >> > >> That's dodgy code, someone needs to look at that. > >> > >> It has an inc in a function called 'create' which seems to suggest its > >> objection creation and we should be using refcount_set() instead. > >> > >> Then again, it looks like you can call this 'create' method multiple > >> times, each time returning the same static object, so refcount_set() > >> would not be correct. > >> > >> Using a refcount on a static object is weird of course, so this is bound > >> to give trouble. > > > > I have reverted this one back to atomic and added it to the tracking doc. > > The problem for this one is that it is not always used as static and in other cases > > it is even initialized correctly to 1, but this static case seems to be special one > giving troubles... > > > > Last week I also fixed all the warnings/errors that test infra gave. The question > that comes is what next? How do we really test this further apart from just booting > this up? > > Which tree has all the fixes? I can refresh my kernel.org tree and let > 0day grind on it, then we can start getting acks and I can push it > into -next via my KSPP tree. Here is the tree: https://github.com/ereshetova/linux-stable/commits/refcount_t I would really like to get more runtime testing done for it also, not just asks :)
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