linux-kernel - Re: [PATCH v3 3/3] list_debug: Introduce CONFIG_DEBUG_LIST

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 11 Aug 2023 11:10:49 +0200
From:   Marco Elver <elver@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Miguel Ojeda <ojeda@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com, linux-toolchains@...r.kernel.org
Subject: Re: [PATCH v3 3/3] list_debug: Introduce CONFIG_DEBUG_LIST_MINIMAL

On Thu, 10 Aug 2023 at 22:12, Kees Cook <keescook@...omium.org> wrote:
>
> On Wed, Aug 09, 2023 at 06:32:37PM +0200, Marco Elver wrote:
> > On Wed, Aug 09, 2023 at 11:30AM -0400, Steven Rostedt wrote:
> > [...]
> > >
> > > I would actually prefer DEBUG_LIST to select HARDEN_LIST and not the other
> > > way around. It logically doesn't make sense that HARDEN_LIST would select
> > > DEBUG_LIST. That is, I could by default want HARDEN_LIST always on, but not
> > > DEBUG_LIST (because who knows, it may add other features I don't want). But
> > > then, I may have stumbled over something and want more info, and enable
> > > DEBUG_LIST (while still having HARDEN_LIST) enabled.
> > >
> > > I think you are looking at this from an implementation perspective and not
> > > the normal developer one.
> > >
> > [...]
> > >
> > > That is, if DEBUG_LIST is enabled, we always call the
> > > __list_add_valid_or_report(), but if only HARDEN_LIST is enabled, then we
> > > do the shortcut.
> >
> > Good point - I think this is better. See below tentative v4.
> >
> > Kees: Does that also look more like what you had in mind?
>
> Yeah, this looks good. My only nit would be a naming one. All the
> other hardening features are named "HARDENED", but perhaps the "ED"
> is redundant in the others. Still, consistency seems nicer. What do you
> think of CONFIG_LIST_HARDENED ? (The modern trend for Kconfig naming tends
> to keep the subsystem name first and then apply optional elements after.)

Naming is a bit all over. :-/
I agree with the <subsystem>_<suboption> scheme, generally. I think
initially I tried to keep the name shorter, and also find a good
counter-part to DEBUG_<suboption>, therefore HARDEN_LIST.

Let's just change it to CONFIG_LIST_HARDENED, given the existing
"HARDENED" options.

I don't have a strong preference.

> One note: do the LKDTM list hardening tests still pass? i.e.
> CORRUPT_LIST_ADD
> CORRUPT_LIST_DEL

Yes, they do. Though I need to also adjust BUG_ON_DATA_CORRUPTION to
select LIST_HARDENED, and the test should check for the new option
(which is implied by DEBUG_LIST now). There will be an additional
patch to adjust that.

> > [...]
> > +             /*
> > +              * With the hardening version, elide checking if next and prev
> > +              * are NULL, LIST_POISON1 or LIST_POISON2, since the immediate
> > +              * dereference of them below would result in a fault.
> > +              */
> > +             if (likely(prev->next == entry && next->prev == entry))
> > +                     return true;
>
> I'm not super excited about skipping those checks, since they are
> values that can be reached through kernel list management confusion. If
> an attacker is using a system where the zero-page has been mapped
> and is accessible (i.e. lacking SMAP etc), then attacks could still
> be constructed. However, I do recognize this chain of exploitation
> prerequisites is getting rather long, so probably this is a reasonable
> trade off on modern systems.

Sure, it's a trade-off for systems which do have the bare minimum of
modern hardware security features.