linux-kernel - Re: [RFC PATCH 00/30] Code tagging framework and applications

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: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJuCfpF4Meeo5b=ZTGe+YDCd9-jJ+WUazpJzaq7stOu2=1oP9Q@mail.gmail.com>
Date:   Mon, 5 Sep 2022 11:07:25 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Davidlohr Bueso <dave@...olabs.net>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R. Howlett" <liam.howlett@...cle.com>,
        David Vernet <void@...ifault.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, mcgrof@...nel.org,
        masahiroy@...nel.org, nathan@...nel.org, changbin.du@...el.com,
        ytcoode@...il.com, Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Christopher Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, 42.hyeyoo@...il.com,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>, arnd@...db.de,
        jbaron@...mai.com, David Rientjes <rientjes@...gle.com>,
        Minchan Kim <minchan@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        kernel-team <kernel-team@...roid.com>,
        linux-mm <linux-mm@...ck.org>, iommu@...ts.linux.dev,
        kasan-dev@...glegroups.com, io-uring@...r.kernel.org,
        linux-arch@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-bcache@...r.kernel.org, linux-modules@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications

On Mon, Sep 5, 2022 at 1:58 AM Marco Elver <elver@...gle.com> wrote:
>
> On Mon, 5 Sept 2022 at 10:12, Michal Hocko <mhocko@...e.com> wrote:
> > On Sun 04-09-22 18:32:58, Suren Baghdasaryan wrote:
> > > On Thu, Sep 1, 2022 at 12:15 PM Michal Hocko <mhocko@...e.com> wrote:
> > [...]
> > > > Yes, tracking back the call trace would be really needed. The question
> > > > is whether this is really prohibitively expensive. How much overhead are
> > > > we talking about? There is no free lunch here, really.  You either have
> > > > the overhead during runtime when the feature is used or on the source
> > > > code level for all the future development (with a maze of macros and
> > > > wrappers).
> > >
> > > As promised, I profiled a simple code that repeatedly makes 10
> > > allocations/frees in a loop and measured overheads of code tagging,
> > > call stack capturing and tracing+BPF for page and slab allocations.
> > > Summary:
> > >
> > > Page allocations (overheads are compared to get_free_pages() duration):
> > > 6.8% Codetag counter manipulations (__lazy_percpu_counter_add + __alloc_tag_add)
> > > 8.8% lookup_page_ext
> > > 1237% call stack capture
> > > 139% tracepoint with attached empty BPF program
> >
> > Yes, I am not surprised that the call stack capturing is really
> > expensive comparing to the allocator fast path (which is really highly
> > optimized and I suspect that with 10 allocation/free loop you mostly get
> > your memory from the pcp lists). Is this overhead still _that_ visible
> > for somehow less microoptimized workloads which have to take slow paths
> > as well?
> >
> > Also what kind of stack unwinder is configured (I guess ORC)? This is
> > not my area but from what I remember the unwinder overhead varies
> > between ORC and FP.
> >
> > And just to make it clear. I do realize that an overhead from the stack
> > unwinding is unavoidable. And code tagging would logically have lower
> > overhead as it performs much less work. But the main point is whether
> > our existing stack unwiding approach is really prohibitively expensive
> > to be used for debugging purposes on production systems. I might
> > misremember but I recall people having bigger concerns with page_owner
> > memory footprint than the actual stack unwinder overhead.
>
> This is just to point out that we've also been looking at cheaper
> collection of the stack trace (for KASAN and other sanitizers). The
> cheapest way to unwind the stack would be a system with "shadow call
> stack" enabled. With compiler support it's available on arm64, see
> CONFIG_SHADOW_CALL_STACK. For x86 the hope is that at one point the
> kernel will support CET, which newer Intel and AMD CPUs support.
> Collecting the call stack would then be a simple memcpy.

Thanks for the note Marco! I'll check out the CONFIG_SHADOW_CALL_STACK
on Android.